513144 - Need API to copy the loaded data from one video element to another one with the same source

Status: RESOLVED FIXED

(Core :: Audio/Video, defect, P1)

Comment 1

[Robert O'Callahan (:roc) (email my personal email if necessary)]

I would quite like to just implement this by adding no new API, just make cloneNode on a media element clone most of the underlying decoder state. It seems that no spec says whether this is right or not. I just sent a message to WHATWG to at least find out which spec is responsible...

In the meantime I guess I'll assume that I should add this to cloneNode.

Comment 2

[Robert O'Callahan (:roc) (email my personal email if necessary)]

I guess if we do it this way, we'll have to sanitize the clone by manually removing all event handler attributes and posssibly in other ways. But I think that should be OK.

Comment 3

[Dão Gottwald [:dao]]

cloneNode sounds good to me. I think this was even the first thing I tried, before I copied the currentSrc.

Comment 4

[Olli Pettay [:smaug][[e-mail]]]

(In reply to comment #2)
> I guess if we do it this way, we'll have to sanitize the clone by manually
> removing all event handler attributes
Why? cloning a node should clone all the attributes too.
Event listeners aren't copied.

Comment 5

[Robert O'Callahan (:roc) (email my personal email if necessary)]

Right, I mean the fullscreen video code will have to remove on* attributes to ensure those event handlers don't fire.

Comment 6

[Robert O'Callahan (:roc) (email my personal email if necessary)]

Actually it's probably best not to tie this to cloneNode for now. I'll create a new method, nsIDOMHTMLMediaElement::mozCloneMedia or something.

The way I'm implementing this is to first refactor the decoder Load methods so that nsHTMLMediaElement creates the nsMediaStream and passes it into the decoder's Load. Then I'll implement nsMediaStream::Clone which will clone the underlying cached blocks for nsMediaChannelStream, and create a new channel for the original URI. Then I'll implement mozCloneMedia by a) cloning the element, b) immediately creating an mDecoder of the same type as the original, c) cloning the original's nsMediaStream and d) passing the new stream into the new decoder's Load, passing null for aStreamListener. The decoder will then Open() the media stream, which will make nsMediaStream open its channel itself (much like we do when we have to reopen the channel for a seek operation). The important thing is that the decoder can start consuming cached data immediately, before the new channel has actually connected to a server.

If the start of the stream containing headers has been discarded from cache, playback and seeking will be delayed while we refetch that data. Hopefully that won't be a major problem.

Comment 7

[cajbir (:cajbir)]

CC'd Mike to take note of comment 6 since the refactoring of Load will affect his GStreamer backend.

Comment 8

[Robert O'Callahan (:roc) (email my personal email if necessary)]

I've got this working!

I decided that copying the media cache blocks would be bad --- consumes unnecessary memory and disk space, and could take a while, which we don't want to happen on the main thread. So I bit the bullet and taught the media cache how to handle blocks that belong to multiple streams at the same time. This was not easy, since a block that is readahead for one stream might be already-played for another stream. But the cache architecture extended to handle this without too much pain, so I'm quite pleased with myself.

Right now once you've cloned the data the two streams are independent. In particular they both keep reading and blocks read by one stream after the clone are not available to the other stream. I should probably fix that, but not yet, since it adds extra complexity.

Right now the API is video.mozCloneData(), returning a new video element. I think a better API would be video.mozLoadFrom(video2), which you can use on an existing video element. It's sort of like load() except that it bypasses the entire resource selection algorithm and just grabs the currentSrc and buffered data from video2. So I'll fix things up to do that.

Comment 9

[Robert O'Callahan (:roc) (email my personal email if necessary)]

Attachment: Part 1: decoder cleanup

-- Move ownership of the Ogg decoder's nsMediaStream out from nsChannelReader to nsOggDecoder
-- Also remove unnecessary mNotifyOnShutdown flag from nsOggDecoder and nsWaveDecoder
-- Since Load can only be called once after Init, remove unnecessary initialization of variables in Load and move some code up from Load to Init in both backends to simplify Load (in particular stuff that happens before creating the nsMediaStream, since soon I'm going to move that out of Load altogether)

Comment 10

[Robert O'Callahan (:roc) (email my personal email if necessary)]

Attachment: Part 2: remove mURI from decoders

No need to store mURI in the decoders, since nsMediaStream holds onto it. Change nsMediaDecoder::GetCurrentURI to GetCurrentStream so nsHTMLMediaElement::GetCurrentSrc can the URI directly from the stream.

Comment 11

[Robert O'Callahan (:roc) (email my personal email if necessary)]

Attachment: Part 3: Split nsMediaStream::Open into Create and Open

Split static nsMediaStream::Open into static nsMediaStream::Create and nonstatic nsMediaStream::Open. Move call to NS_GetFinalChannelURI down into nsMediaStream::Create.

This gets things ready so that we can hoist the nsMediaStream::Create call up out of the decoders into nsHTMLMediaElement (next patch). We need to do this because when we start cloning streams, nsHTMLMediaElement will need to create the stream in a different way.

Comment 12

[Robert O'Callahan (:roc) (email my personal email if necessary)]

Attachment: Part 4: hoist nsMediaStream::Create call into nsHTMLMediaElement

As per last comment, make nsHTMLMediaElement responsible for creating the nsMediaStream.

Comment 13

[cajbir (:cajbir)]

Comment on attachment 400667 [details] [diff] [review]
Part 1: decoder cleanup

>+   * Initialize the reader with the given decoder and media stream.
>+   * This takes ownership of aStream.
> ...
>+  void Init(nsMediaStream* aStream);

The comment seems to be wrong. There is no 'given decoder'.

Comment 14

[Robert O'Callahan (:roc) (email my personal email if necessary)]

Attachment: Part 5: basic implementation of mozLoadFrom

This is the basic implementation of mozLoadFrom. It's a lot like LoadWithChannel except we clone the decoder and its nsMediaStream from the existing element. In this patch the nsMediaStream cloning is dumb, it effectively opens a new stream and no cached content is shared.

Comment 15

[Robert O'Callahan (:roc) (email my personal email if necessary)]

Attachment: Part 6: Rewrite nsMediaCache block lists so a block can be in more than one list at a time

Now it gets interesting.

Currently nsMediaCache blocks can belong to at most one list at a time: the global free list, the global "played" list, the global "used metadata" list, or the per-stream "readahead" list.

When blocks can belong to more than one stream, they can be on more than one list. For example a block might be "played" with respect to one stream (because that stream's play point is past the block), but "readahead" with respect to another stream (because the other stream's play point is before the block). So here I rewrite BlockList to not use prev/next pointers stored in the block. Instead each BlockList has a hashtable mapping blocks to the linked-list entry for each block. This is a fairly straightforward data structure change that shouldn't change any behaviour.

Comment 16

[cajbir (:cajbir)]

Comment on attachment 400670 [details] [diff] [review]
Part 4: hoist nsMediaStream::Create call into nsHTMLMediaElement

From Part 4 patch:

>-nsWaveDecoder::Load(nsIChannel* aChannel, nsIStreamListener** aStreamListener)
>+nsWaveDecoder::Load(nsMediaStream* aStream, nsIStreamListener** aStreamListener)
> {
>-  NS_ASSERTION(aChannel, "A channel is required");

Assert that a stream is required?

Comment 17

[Robert O'Callahan (:roc) (email my personal email if necessary)]

Attachment: Part 7: Support multiple block owners

This is the hard bit.

On trunk a block is owned by at most one stream. This patch lets each block belong to zero or more streams. A block is free when it has no owners.

This patch also makes the "played" and "metadata" lists per-stream instead of global. This is because, as I mentioned before, a block can be "played" with respect to one stream but "readahead" with respect to another stream.

The data we used to associate with a block --- the stream it belongs to, its "class" (readahead, played, metadata), its offset within the stream, and its last use time --- are all now replicated once per owning stream, since they describe the block's relationship with each owning stream, which is why I called the struct containing that data BlockOwner, although I'm not super happy with that name. I'd be glad for you to suggest a better one.

Wherever the trunk code looks at "the stream" for a block, we need to do something different. In many cases the right thing to do is to iterate over all the block's owners. For example BlockIsReusable loops over all owners to see if any of them are pinned or about to read from the block.

In other cases like GetListForBlock we need to pass in which stream we care about, or pass in the block's BlockOwner for the stream we care about.

FreeBlock is tricky. Some callers of FreeBlock need to tear down the block no matter what, so all owners lose access to it. Other callers just want to note that a particular stream no longer needs the block. For the latter callers I'm creating a new function RemoveBlockOwner.

PredictNextUse loops over all owners and returns the *earliest* time that any owner predicts it will use the block.

Comment 18

[Robert O'Callahan (:roc) (email my personal email if necessary)]

(In reply to comment #13)
> (From update of attachment 400667 [details] [diff] [review])
> >+   * Initialize the reader with the given decoder and media stream.
> >+   * This takes ownership of aStream.
> > ...
> >+  void Init(nsMediaStream* aStream);
> 
> The comment seems to be wrong. There is no 'given decoder'.

Yes, I removed it without updating the comment. I'll fix the comment.

(In reply to comment #16)
> (From update of attachment 400670 [details] [diff] [review])
> From Part 4 patch:
> 
> >-nsWaveDecoder::Load(nsIChannel* aChannel, nsIStreamListener** aStreamListener)
> >+nsWaveDecoder::Load(nsMediaStream* aStream, nsIStreamListener** aStreamListener)
> > {
> >-  NS_ASSERTION(aChannel, "A channel is required");
> 
> Assert that a stream is required?

Sure.

Comment 19

[Robert O'Callahan (:roc) (email my personal email if necessary)]

Attachment: Part 8: Actually support cache stream cloning

Make nsMediaChannelStream::CloneData clone the underlying cache stream, which adds the new stream as co-owner of all the nsMediaCache blocks currently cached for the original stream. All these blocks are readahead blocks for the new stream, since the new stream is at its beginning.

Makes nsMediaCacheStream::Init do nothing on already-initialized streams, since nsMediaChannelStream::Open calls Init on the cache stream and it would be complicated to stop doing that, and a cloned cache stream will be already initialized before it reaches nsMediaChannelStream::Open.

Also, use NS_NEW_RUNNABLE_METHOD instead of the SuspendedStatusChanged class.

With this patch, mozLoadFrom will give the destination element access to all the cached data for the original element. However, any data subsequently loaded by either element will not be shared. So in the normal case you end up with two connections both reading ahead to get the same data, which is suboptimal.

Comment 20

[Robert O'Callahan (:roc) (email my personal email if necessary)]

Attachment: Part 9: allow streams to share data loaded after the initial clone

This patch fixes the problem I just mentioned.

We need to be able to identify streams that are reading the same underlying resource. I add mResourceID to each stream. Normal streams get a fresh unique ID. Cloned streams get the ID of their source.

ResourceStreamIterator lets you iterate over all the streams for a given resource ID. Right now this is dumb array traversal but if we need to optimize for large numbers of streams we could use a hashtable.

nsMediaCache::Update is modified so that if multiple streams all want to read from the same point in the resource, only one of them is allowed to read and the others are all suspended. This prevents the duplicate read problem that I mentioned above.

nsMediaCache::AllocateAndWriteBlock is modified so that the newly loaded block is added to all streams that share the resource ID of the stream that loaded it. Note that the block may be added as a different class for each stream; e.g. a block might be loaded as readahead for one stream, but be counted as "played" (behind the current playback position) for another.

nsMediaCacheStream::NotifyDataReceived needs to broadcast principal updates and stream length updates to all affected streams.

On trunk nsMediaChannelStream::OnDataAvailable is responsible for notifying the stream's decoder that data has arrived so progress events get fired and readyState changes happen. That's not enough anymore since a single OnDataAvailable can mean data has arrived for many decoders/elements. So we stop sending the notifications there and instead have the media cache call CacheClientNotifyDataReceived on every nsMediaChannelStream that gets affected. The tricky bit is that we don't want CacheClientNotifyDataReceived to do anything that might take a lock, since it's called with the media cache lock held. To avoid problems we have to post an event to notify the decoder asynchronously. Similar deal for CacheClientNotifyDataEnded.

I'm moving the Progress(FALSE) call that used to be in OnDataAvailable into the decoders' NotifyBytesDownloaded.

With this patch things are basically great. After calling mozLoadFrom we will generally only need one connection to feed both elements, although if you start seeking around we will allow each connection to read from different parts of the resource.

Comment 21

[Robert O'Callahan (:roc) (email my personal email if necessary)]

Attachment: Part 10: Fix Wave backend bug

The change in timing of notifications in the previous patch seems to have exposed a bug in the Wave decoder (yay tests!). When playback ends, it was calling mElement->PlaybackEnded without calling UpdateReadyStateForData, which means we could be in the ended state while readyState is still HAVE_FUTURE_DATA or HAVE_ENOUGH_DATA. But readyState should be in HAVE_CURRENT_DATA when we've ended. The fix is simple and safe.

Comment 22

[Robert O'Callahan (:roc) (email my personal email if necessary)]

After all these patches the general situation should be that if a resource block is important enough to be cached by one of the streams for the resource, it will be cached and accessible to all of them. However, we don't do anything to prioritize a block that can be used by many streams over a block that can only be used by one stream.

Another feature that could be added in the future is the ability to share resource data even for streams that are not cloned, i.e. streams that HTTP caching tells us should be identical.

Comment 23

[Johnny Stenback (:jst)]

Comment on attachment 400672 [details] [diff] [review]
Part 5: basic implementation of mozLoadFrom

sr=jst

Comment 24

[cajbir (:cajbir)]

Comment on attachment 400675 [details] [diff] [review]
Part 7: Support multiple block owners

># HG changeset patch
># User Robert O'Callahan <[e-mail]>
># Date 1252981844 -43200
># Node ID d7cdd8e1b04122047255fd7433f3a7b4cd060895
># Parent  ee7ff885a913839ccb5a5997483e9e997d2aec0a
>imported patch bug513144-multiple-owners
>
>diff --git a/content/media/nsMediaCache.cpp b/content/media/nsMediaCache.cpp
>--- a/content/media/nsMediaCache.cpp
>+++ b/content/media/nsMediaCache.cpp
>@@ -1,9 +1,9 @@
>- /* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
>+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
> /* vim:set ts=2 sw=2 sts=2 et cindent: */
> /* ***** BEGIN LICENSE BLOCK *****
>  * Version: MPL 1.1/GPL 2.0/LGPL 2.1
>  *
>  * The contents of this file are subject to the Mozilla Public License Version
>  * 1.1 (the "License"); you may not use this file except in compliance with
>  * the License. You may obtain a copy of the License at
>  * http://www.mozilla.org/MPL/
>@@ -152,18 +152,18 @@ public:
>   // will do that if necessary. The caller will call QueueUpdate().
>   void NoteSeek(nsMediaCacheStream* aStream, PRInt64 aOldOffset);
>   // Notify the cache that a block has been read from. This is used
>   // to update last-use times. The block may not actually have a
>   // cache entry yet since Read can read data from a stream's
>   // in-memory mPartialBlockBuffer while the block is only partly full,
>   // and thus hasn't yet been committed to the cache. The caller will
>   // call QueueUpdate().
>-  void NoteBlockUsage(PRInt32 aBlockIndex, nsMediaCacheStream::ReadMode aMode,
>-                      TimeStamp aNow);
>+  void NoteBlockUsage(nsMediaCacheStream* aStream, PRInt32 aBlockIndex,
>+                      nsMediaCacheStream::ReadMode aMode, TimeStamp aNow);
> 
>   // This queues a call to Update() on the main thread.
>   void QueueUpdate();
> 
>   // Updates the cache state asynchronously on the main thread:
>   // -- try to trim the cache back to its desired size, if necessary
>   // -- suspend channels that are going to read data that's lower priority
>   // than anything currently cached
>@@ -192,67 +192,79 @@ protected:
>   // aMaxSearchBlockIndex are considered. If aForStream is non-null,
>   // then aForStream and aForStreamBlock indicate what media data will
>   // be placed; FindReusableBlock will favour returning free blocks
>   // near other blocks for that point in the stream.
>   PRInt32 FindReusableBlock(TimeStamp aNow,
>                             nsMediaCacheStream* aForStream,
>                             PRInt32 aForStreamBlock,
>                             PRInt32 aMaxSearchBlockIndex);
>+  PRBool BlockIsReusable(PRInt32 aBlockIndex);
>   // Given a list of blocks sorted with the most reusable blocks at the
>   // end, find the last block whose stream is not pinned (if any)
>   // and whose cache entry index is less than aBlockIndexLimit
>   // and append it to aResult.
>   void AppendMostReusableBlock(BlockList* aBlockList,
>                                nsTArray<PRUint32>* aResult,
>                                PRInt32 aBlockIndexLimit);
> 
>   enum BlockClass {
>-    // block belongs to mFreeBlockList because it's free
>-    FREE_BLOCK,
>     // block belongs to mMetadataBlockList because data has been consumed
>     // from it in "metadata mode" --- in particular blocks read during
>     // Ogg seeks go into this class. These blocks may have played data
>     // in them too.
>     METADATA_BLOCK,
>     // block belongs to mPlayedBlockList because its offset is
>     // less than the stream's current reader position
>     PLAYED_BLOCK,
>     // block belongs to the stream's mReadaheadBlockList because its
>     // offset is greater than or equal to the stream's current
>     // reader position
>     READAHEAD_BLOCK
>   };
> 
>-  struct Block {
>-    Block() : mStream(nsnull), mClass(FREE_BLOCK) {}
>+  struct BlockOwner {
>+    BlockOwner() : mStream(nsnull), mClass(READAHEAD_BLOCK) {}
> 
>     // The stream that owns this block, or null if the block is free.
>     nsMediaCacheStream* mStream;
>     // The block index in the stream. Valid only if mStream is non-null.
>     PRUint32            mStreamBlock;
>     // Time at which this block was last used. Valid only if
>     // mClass is METADATA_BLOCK or PLAYED_BLOCK.
>     TimeStamp           mLastUseTime;
>-    // The class is FREE_BLOCK if and only if mStream is null
>     BlockClass          mClass;
>   };
> 
>+  struct Block {
>+    // Free blocks have an empty mOwners array
>+    nsTArray<BlockOwner> mOwners;
>+  };
>+
>   // Get the BlockList that the block should belong to given its
>-  // current mClass and mStream
>-  BlockList* GetListForBlock(Block* aBlock);
>-  // Add the block to the free list, mark it FREE_BLOCK, and mark
>-  // its stream (if any) as not having the block in cache
>+  // current owner
>+  BlockList* GetListForBlock(BlockOwner* aBlock);
>+  // Get the BlockOwner for the given block index and owning stream
>+  // (returns null if the stream does not own the block)
>+  BlockOwner* GetBlockOwner(PRInt32 aBlockIndex, nsMediaCacheStream* aStream);
>+  // Returns true iff the block is free
>+  PRBool IsBlockFree(PRInt32 aBlockIndex)
>+  { return mIndex[aBlockIndex].mOwners.IsEmpty(); }
>+  // Add the block to the free list and mark its streams as not having
>+  // the block in cache
>   void FreeBlock(PRInt32 aBlock);
>+  // Mark aStream as not having the block, removing it as an owner. If
>+  // the block has no more owners it's added to the free list.
>+  void RemoveBlockOwner(PRInt32 aBlockIndex, nsMediaCacheStream* aStream);
>   // Swap all metadata associated with the two blocks. The caller
>   // is responsible for swapping up any cache file state.
>   void SwapBlocks(PRInt32 aBlockIndex1, PRInt32 aBlockIndex2);
>-  // Insert the block into the readahead block list for its stream
>+  // Insert the block into the readahead block list for the stream
>   // at the right point in the list.
>-  void InsertReadaheadBlock(PRInt32 aBlockIndex);
>+  void InsertReadaheadBlock(BlockOwner* aBlockOwner, PRInt32 aBlockIndex);
> 
>   // Guess the duration until block aBlock will be next used
>   TimeDuration PredictNextUse(TimeStamp aNow, PRInt32 aBlock);
>   // Guess the duration until the next incoming data on aStream will be used
>   TimeDuration PredictNextUseForIncomingData(nsMediaCacheStream* aStream);
> 
>   // Truncate the file and index array if there are free blocks at the
>   // end
>@@ -269,20 +281,16 @@ protected:
>   nsTArray<Block> mIndex;
>   // The file descriptor of the cache file. The file will be deleted
>   // by the operating system when this is closed.
>   PRFileDesc*     mFD;
>   // The current file offset in the cache file.
>   PRInt64         mFDCurrentPos;
>   // The list of free blocks; they are not ordered.
>   BlockList       mFreeBlocks;
>-  // The list of metadata blocks; the first block is the most recently used
>-  BlockList       mMetadataBlocks;
>-  // The list of played-back blocks; the first block is the most recently used
>-  BlockList       mPlayedBlocks;
>   // True if an event to run Update() has been queued but not processed
>   PRPackedBool    mUpdateQueued;
> #ifdef DEBUG
>   PRPackedBool    mInUpdate;
> #endif
> };
> 
> // There is at most one media cache (although that could quite easily be
>@@ -611,17 +619,17 @@ PRInt32
> nsMediaCache::FindBlockForIncomingData(TimeStamp aNow,
>                                        nsMediaCacheStream* aStream)
> {
>   PR_ASSERT_CURRENT_THREAD_IN_MONITOR(mMonitor);
> 
>   PRInt32 blockIndex = FindReusableBlock(aNow, aStream,
>       aStream->mChannelOffset/BLOCK_SIZE, PR_INT32_MAX);
> 
>-  if (blockIndex < 0 || mIndex[blockIndex].mStream) {
>+  if (blockIndex < 0 || !IsBlockFree(blockIndex)) {
>     // The block returned is already allocated.
>     // Don't reuse it if a) there's room to expand the cache or
>     // b) the data we're going to store in the free block is not higher
>     // priority than the data already stored in the free block.
>     // The latter can lead us to go over the cache limit a bit.
>     if ((mIndex.Length() < PRUint32(GetMaxBlocks()) || blockIndex < 0 ||
>          PredictNextUseForIncomingData(aStream) >= PredictNextUse(aNow, blockIndex))) {
>       blockIndex = mIndex.Length();
>@@ -630,34 +638,46 @@ nsMediaCache::FindBlockForIncomingData(T
>       mFreeBlocks.AddFirstBlock(blockIndex);
>       return blockIndex;
>     }
>   }
> 
>   return blockIndex;
> }
> 
>+PRBool
>+nsMediaCache::BlockIsReusable(PRInt32 aBlockIndex)
>+{
>+  Block* block = &mIndex[aBlockIndex];
>+  for (PRUint32 i = 0; i < block->mOwners.Length(); ++i) {
>+    nsMediaCacheStream* stream = block->mOwners[i].mStream;
>+    if (stream->mPinCount >= 0 ||
>+        stream->mStreamOffset/BLOCK_SIZE == block->mOwners[i].mStreamBlock) {
>+      return PR_FALSE;
>+    }
>+  }
>+  return PR_TRUE;
>+}
>+
> void
> nsMediaCache::AppendMostReusableBlock(BlockList* aBlockList,
>                                       nsTArray<PRUint32>* aResult,
>                                       PRInt32 aBlockIndexLimit)
> {
>   PR_ASSERT_CURRENT_THREAD_IN_MONITOR(mMonitor);
> 
>   PRInt32 blockIndex = aBlockList->GetLastBlock();
>   if (blockIndex < 0)
>     return;
>   do {
>     // Don't consider blocks for pinned streams, or blocks that are
>-    // beyond the specified limit, or the block that contains its stream's
>+    // beyond the specified limit, or a block that contains a stream's
>     // current read position (such a block contains both played data
>     // and readahead data)
>-    nsMediaCacheStream* stream = mIndex[blockIndex].mStream;
>-    if (stream->mPinCount == 0 && blockIndex < aBlockIndexLimit &&
>-        stream->mStreamOffset/BLOCK_SIZE != mIndex[blockIndex].mStreamBlock) {
>+    if (blockIndex < aBlockIndexLimit && BlockIsReusable(blockIndex)) {
>       aResult->AppendElement(blockIndex);
>       return;
>     }
>     blockIndex = aBlockList->GetPrevBlock(blockIndex);
>   } while (blockIndex >= 0);
> }
> 
> PRInt32
>@@ -672,17 +692,17 @@ nsMediaCache::FindReusableBlock(TimeStam
> 
>   if (aForStream && aForStreamBlock > 0 &&
>       PRUint32(aForStreamBlock) <= aForStream->mBlocks.Length()) {
>     PRInt32 prevCacheBlock = aForStream->mBlocks[aForStreamBlock - 1];
>     if (prevCacheBlock >= 0) {
>       PRUint32 freeBlockScanEnd =
>         PR_MIN(length, prevCacheBlock + FREE_BLOCK_SCAN_LIMIT);
>       for (PRUint32 i = prevCacheBlock; i < freeBlockScanEnd; ++i) {
>-        if (mIndex[i].mClass == FREE_BLOCK)
>+        if (IsBlockFree(i))
>           return i;
>       }
>     }
>   }
> 
>   if (!mFreeBlocks.IsEmpty()) {
>     PRInt32 blockIndex = mFreeBlocks.GetFirstBlock();
>     do {
>@@ -692,168 +712,210 @@ nsMediaCache::FindReusableBlock(TimeStam
>     } while (blockIndex >= 0);
>   }
> 
>   // Build a list of the blocks we should consider for the "latest
>   // predicted time of next use". We can exploit the fact that the block
>   // linked lists are ordered by increasing time of next use. This is
>   // actually the whole point of having the linked lists.
>   nsAutoTArray<PRUint32,8> candidates;
>-  AppendMostReusableBlock(&mMetadataBlocks, &candidates, length);
>-  AppendMostReusableBlock(&mPlayedBlocks, &candidates, length);
>   for (PRUint32 i = 0; i < mStreams.Length(); ++i) {
>     nsMediaCacheStream* stream = mStreams[i];
>-    // Don't consider a) blocks for pinned streams or b) blocks in
>-    // non-seekable streams that contain data ahead of the current reader
>-    // position. In the latter case, if we remove the block we won't be
>-    // able to seek back to read it later.
>-    if (!stream->mReadaheadBlocks.IsEmpty() && stream->mIsSeekable &&
>-        stream->mPinCount == 0) {
>-      // Find a readahead block that's in the given limit
>-      PRInt32 blockIndex = stream->mReadaheadBlocks.GetLastBlock();
>-      do {
>-        if (PRUint32(blockIndex) < length) {
>-          candidates.AppendElement(blockIndex);
>-          break;
>-        }
>-        blockIndex = stream->mReadaheadBlocks.GetPrevBlock(blockIndex);
>-      } while (blockIndex >= 0);
>+    if (stream->mPinCount > 0) {
>+      // No point in even looking at this stream's blocks
>+      continue;
>+    }
>+
>+    AppendMostReusableBlock(&stream->mMetadataBlocks, &candidates, length);
>+    AppendMostReusableBlock(&stream->mPlayedBlocks, &candidates, length);
>+
>+    // Don't consider readahead blocks in non-seekable streams. If we
>+    // remove the block we won't be able to seek back to read it later.
>+    if (stream->mIsSeekable) {
>+      AppendMostReusableBlock(&stream->mReadaheadBlocks, &candidates, length);
>     }
>   }
> 
>   TimeDuration latestUse;
>   PRInt32 latestUseBlock = -1;
>   for (PRUint32 i = 0; i < candidates.Length(); ++i) {
>     TimeDuration nextUse = PredictNextUse(aNow, candidates[i]);
>     if (nextUse > latestUse) {
>       latestUse = nextUse;
>       latestUseBlock = candidates[i];
>     }
>   }
> 
>-#ifdef DEBUG
>-  for (PRUint32 blockIndex = 0; blockIndex < length; ++blockIndex) {
>-    Block* block = &mIndex[blockIndex];
>-    nsMediaCacheStream* stream = block->mStream;
>-    NS_ASSERTION(!stream || stream->mPinCount > 0 ||
>-                 (!stream->mIsSeekable && block->mClass == READAHEAD_BLOCK) ||
>-                 stream->mStreamOffset/BLOCK_SIZE == block->mStreamBlock ||
>-                 PredictNextUse(aNow, blockIndex) <= latestUse,
>-                 "We missed a block that should be replaced");
>-  }
>-#endif
>-
>   return latestUseBlock;
> }
> 
> nsMediaCache::BlockList*
>-nsMediaCache::GetListForBlock(Block* aBlock)
>+nsMediaCache::GetListForBlock(BlockOwner* aBlock)
> {
>   switch (aBlock->mClass) {
>-  case FREE_BLOCK:
>-    NS_ASSERTION(!aBlock->mStream, "Free block has a stream?");
>-    return &mFreeBlocks;
>   case METADATA_BLOCK:
>     NS_ASSERTION(aBlock->mStream, "Metadata block has no stream?");
>-    return &mMetadataBlocks;
>+    return &aBlock->mStream->mMetadataBlocks;
>   case PLAYED_BLOCK:
>     NS_ASSERTION(aBlock->mStream, "Metadata block has no stream?");
>-    return &mPlayedBlocks;
>+    return &aBlock->mStream->mPlayedBlocks;
>   case READAHEAD_BLOCK:
>     NS_ASSERTION(aBlock->mStream, "Readahead block has no stream?");
>     return &aBlock->mStream->mReadaheadBlocks;
>   default:
>     NS_ERROR("Invalid block class");
>     return nsnull;
>   }
> }
> 
>+nsMediaCache::BlockOwner*
>+nsMediaCache::GetBlockOwner(PRInt32 aBlockIndex, nsMediaCacheStream* aStream)
>+{
>+  Block* block = &mIndex[aBlockIndex];
>+  for (PRUint32 i = 0; i < block->mOwners.Length(); ++i) {
>+    if (block->mOwners[i].mStream == aStream)
>+      return &block->mOwners[i];
>+  }
>+  return nsnull;
>+}
>+
> void
> nsMediaCache::SwapBlocks(PRInt32 aBlockIndex1, PRInt32 aBlockIndex2)
> {
>   PR_ASSERT_CURRENT_THREAD_IN_MONITOR(mMonitor);
> 
>   Block* block1 = &mIndex[aBlockIndex1];
>   Block* block2 = &mIndex[aBlockIndex2];
> 
>-  Block tmp = *block1;
>-  *block1 = *block2;
>-  *block2 = tmp;
>+  block1->mOwners.SwapElements(block2->mOwners);
> 
>   // Now all references to block1 have to be replaced with block2 and
>-  // vice versa
>-
>-  if (block1->mStream) {
>-    block1->mStream->mBlocks[block1->mStreamBlock] = aBlockIndex1;
>-  }
>-  if (block2->mStream) {
>-    block2->mStream->mBlocks[block2->mStreamBlock] = aBlockIndex2;
>+  // vice versa.
>+  // First update stream references to blocks via mBlocks.
>+  const Block* blocks[] = { block1, block2 };
>+  PRInt32 blockIndices[] = { aBlockIndex1, aBlockIndex2 };
>+  for (PRInt32 i = 0; i < 2; ++i) {
>+    for (PRUint32 j = 0; j < blocks[i]->mOwners.Length(); ++j) {
>+      const BlockOwner* b = &blocks[i]->mOwners[j];
>+      b->mStream->mBlocks[b->mStreamBlock] = blockIndices[i];
>+    }
>   }
> 
>-  BlockList* list1 = GetListForBlock(block1);
>-  list1->NotifyBlockSwapped(aBlockIndex1, aBlockIndex2);
>-  BlockList* list2 = GetListForBlock(block2);
>-  // We have to be careful we don't swap the same reference twice!
>-  if (list1 != list2) {
>-    list2->NotifyBlockSwapped(aBlockIndex1, aBlockIndex2);
>+  // Now update references to blocks in block lists.
>+  mFreeBlocks.NotifyBlockSwapped(aBlockIndex1, aBlockIndex2);
>+
>+  nsTHashtable<nsPtrHashKey<nsMediaCacheStream> > visitedStreams;
>+  visitedStreams.Init();
>+
>+  for (PRInt32 i = 0; i < 2; ++i) {
>+    for (PRUint32 j = 0; j < blocks[i]->mOwners.Length(); ++j) {
>+      nsMediaCacheStream* stream = blocks[i]->mOwners[j].mStream;
>+      // Make sure that we don't update the same stream twice --- that
>+      // would result in swapping the block references back again!
>+      if (visitedStreams.GetEntry(stream))
>+        continue;
>+      visitedStreams.PutEntry(stream);
>+      stream->mReadaheadBlocks.NotifyBlockSwapped(aBlockIndex1, aBlockIndex2);
>+      stream->mPlayedBlocks.NotifyBlockSwapped(aBlockIndex1, aBlockIndex2);
>+      stream->mMetadataBlocks.NotifyBlockSwapped(aBlockIndex1, aBlockIndex2);
>+    }
>   }
> 
>   Verify();
> }
> 
> void
>+nsMediaCache::RemoveBlockOwner(PRInt32 aBlockIndex, nsMediaCacheStream* aStream)
>+{
>+  Block* block = &mIndex[aBlockIndex];
>+  for (PRUint32 i = 0; i < block->mOwners.Length(); ++i) {
>+    BlockOwner* bo = &block->mOwners[i];
>+    if (bo->mStream == aStream) {
>+      GetListForBlock(bo)->RemoveBlock(aBlockIndex);
>+      bo->mStream->mBlocks[bo->mStreamBlock] = -1;
>+      block->mOwners.RemoveElementAt(i);
>+      if (block->mOwners.IsEmpty()) {
>+        mFreeBlocks.AddFirstBlock(aBlockIndex);
>+      }
>+      return;
>+    }
>+  }
>+}
>+
>+void
> nsMediaCache::FreeBlock(PRInt32 aBlock)
> {
>   PR_ASSERT_CURRENT_THREAD_IN_MONITOR(mMonitor);
> 
>   Block* block = &mIndex[aBlock];
>-  GetListForBlock(block)->RemoveBlock(aBlock);
>-  if (block->mStream) {
>-    block->mStream->mBlocks[block->mStreamBlock] = -1;
>+  if (block->mOwners.IsEmpty()) {
>+    // already free
>+    return;
>   }
>-  block->mStream = nsnull;
>-  block->mClass = FREE_BLOCK;
>+
>+  LOG(PR_LOG_DEBUG, ("Released block %d", aBlock));
>+
>+  for (PRUint32 i = 0; i < block->mOwners.Length(); ++i) {
>+    BlockOwner* bo = &block->mOwners[i];
>+    GetListForBlock(bo)->RemoveBlock(aBlock);
>+    bo->mStream->mBlocks[bo->mStreamBlock] = -1;
>+  }
>+  block->mOwners.Clear();
>   mFreeBlocks.AddFirstBlock(aBlock);
>   Verify();
> }
> 
> TimeDuration
> nsMediaCache::PredictNextUse(TimeStamp aNow, PRInt32 aBlock)
> {
>   PR_ASSERT_CURRENT_THREAD_IN_MONITOR(mMonitor);
>+  NS_ASSERTION(!IsBlockFree(aBlock), "aBlock is free");
> 
>   Block* block = &mIndex[aBlock];
>-
>-  switch (block->mClass) {
>-  case METADATA_BLOCK:
>-    // This block should be managed in LRU mode. For metadata we predict
>-    // that the time until the next use is the time since the last use.
>-    return aNow - block->mLastUseTime;
>-  case PLAYED_BLOCK:
>-    // This block should be managed in LRU mode, and we should impose
>-    // a "replay delay" to reflect the likelihood of replay happening
>-    NS_ASSERTION(PRInt64(block->mStreamBlock)*BLOCK_SIZE <
>-                 block->mStream->mStreamOffset,
>-                 "Played block after the current stream position?");
>-    return aNow - block->mLastUseTime +
>+  // Blocks can be belong to multiple streams. The predicted next use
>+  // time is the earliest time predicted by any of the streams.
>+  TimeDuration result;
>+  for (PRUint32 i = 0; i < block->mOwners.Length(); ++i) {
>+    BlockOwner* bo = &block->mOwners[i];
>+    TimeDuration prediction;
>+    switch (bo->mClass) {
>+    case METADATA_BLOCK:
>+      // This block should be managed in LRU mode. For metadata we predict
>+      // that the time until the next use is the time since the last use.
>+      prediction = aNow - bo->mLastUseTime;
>+      break;
>+    case PLAYED_BLOCK:
>+      // This block should be managed in LRU mode, and we should impose
>+      // a "replay delay" to reflect the likelihood of replay happening
>+      NS_ASSERTION(PRInt64(bo->mStreamBlock)*BLOCK_SIZE <
>+                   bo->mStream->mStreamOffset,
>+                   "Played block after the current stream position?");
>+      prediction = aNow - bo->mLastUseTime +
>         TimeDuration::FromSeconds(REPLAY_DELAY);
>-  case READAHEAD_BLOCK: {
>-    PRInt64 bytesAhead =
>-      PRInt64(block->mStreamBlock)*BLOCK_SIZE - block->mStream->mStreamOffset;
>-    NS_ASSERTION(bytesAhead >= 0,
>-                 "Readahead block before the current stream position?");
>-    PRInt64 millisecondsAhead =
>-      bytesAhead*1000/block->mStream->mPlaybackBytesPerSecond;
>-    return TimeDuration::FromMilliseconds(
>-        PR_MIN(millisecondsAhead, PR_INT32_MAX));
>+      break;
>+    case READAHEAD_BLOCK: {
>+      PRInt64 bytesAhead =
>+        PRInt64(bo->mStreamBlock)*BLOCK_SIZE - bo->mStream->mStreamOffset;
>+      NS_ASSERTION(bytesAhead >= 0,
>+                   "Readahead block before the current stream position?");
>+      PRInt64 millisecondsAhead =
>+        bytesAhead*1000/bo->mStream->mPlaybackBytesPerSecond;
>+      prediction = TimeDuration::FromMilliseconds(
>+          PR_MIN(millisecondsAhead, PR_INT32_MAX));
>+      break;
>+    }
>+    default:
>+      NS_ERROR("Invalid class for predicting next use");
>+      return TimeDuration(0);
>+    }
>+    if (i == 0 || prediction < result) {
>+      result = prediction;
>+    }
>   }
>-  default:
>-    NS_ERROR("Invalid class for predicting next use");
>-    return TimeDuration(0);
>-  }
>+  return result;
> }
> 
> TimeDuration
> nsMediaCache::PredictNextUseForIncomingData(nsMediaCacheStream* aStream)
> {
>   PR_ASSERT_CURRENT_THREAD_IN_MONITOR(mMonitor);
> 
>   PRInt64 bytesAhead = aStream->mChannelOffset - aStream->mStreamOffset;
>@@ -895,44 +957,45 @@ nsMediaCache::Update()
>   // blocks (by moving an overflowing block to the main part of the cache,
>   // and then overwriting it with another overflowing block), and we try
>   // to avoid that since it requires HTTP seeks.
>   // We also use this loop to eliminate overflowing blocks from
>   // freeBlockCount.
>   TimeDuration latestPredictedUseForOverflow = 0;
>   for (PRInt32 blockIndex = mIndex.Length() - 1; blockIndex >= maxBlocks;
>        --blockIndex) {
>-    nsMediaCacheStream* stream = mIndex[blockIndex].mStream;
>-    if (!stream) {
>+    if (IsBlockFree(blockIndex)) {
>       // Don't count overflowing free blocks in our free block count
>       --freeBlockCount;
>       continue;
>     }
>     TimeDuration predictedUse = PredictNextUse(now, blockIndex);
>     latestPredictedUseForOverflow = PR_MAX(latestPredictedUseForOverflow, predictedUse);
>   }
> 
>   // Now try to move overflowing blocks to the main part of the cache.
>   for (PRInt32 blockIndex = mIndex.Length() - 1; blockIndex >= maxBlocks;
>        --blockIndex) {
>-    Block* block = &mIndex[blockIndex];
>-    nsMediaCacheStream* stream = block->mStream;
>-    if (!stream)
>+    if (IsBlockFree(blockIndex))
>       continue;
> 
>+    Block* block = &mIndex[blockIndex];
>+    // Try to relocate the block close to other blocks for the first stream.
>+    // There is no point in trying ot make it close to other blocks in
>+    // *all* the streams it might belong to.
>     PRInt32 destinationBlockIndex =
>-      FindReusableBlock(now, stream, block->mStreamBlock, maxBlocks);
>+      FindReusableBlock(now, block->mOwners[0].mStream,
>+                        block->mOwners[0].mStreamBlock, maxBlocks);
>     if (destinationBlockIndex < 0) {
>       // Nowhere to place this overflow block. We won't be able to
>       // place any more overflow blocks.
>       break;
>     }
> 
>-    Block* destinationBlock = &mIndex[destinationBlockIndex];
>-    if (destinationBlock->mClass == FREE_BLOCK ||
>+    if (IsBlockFree(destinationBlockIndex) ||
>         PredictNextUse(now, destinationBlockIndex) > latestPredictedUseForOverflow) {
>       // Reuse blocks in the main part of the cache that are less useful than
>       // the least useful overflow blocks
>       char buf[BLOCK_SIZE];
>       nsresult rv = ReadCacheFileAllBytes(blockIndex*BLOCK_SIZE, buf, sizeof(buf));
>       if (NS_SUCCEEDED(rv)) {
>         rv = WriteCacheFile(destinationBlockIndex*BLOCK_SIZE, buf, BLOCK_SIZE);
>         if (NS_SUCCEEDED(rv)) {
>@@ -940,29 +1003,24 @@ nsMediaCache::Update()
>           LOG(PR_LOG_DEBUG, ("Swapping blocks %d and %d (trimming cache)",
>               blockIndex, destinationBlockIndex));
>           // Swapping the block metadata here lets us maintain the
>           // correct positions in the linked lists
>           SwapBlocks(blockIndex, destinationBlockIndex);
>         } else {
>           // If the write fails we may have corrupted the destination
>           // block. Free it now.
>-          LOG(PR_LOG_DEBUG, ("Released block %d from stream %p block %d(%lld) (trimming cache)",
>-              destinationBlockIndex, destinationBlock->mStream,
>-              destinationBlock->mStreamBlock,
>-              (long long)destinationBlock->mStreamBlock*BLOCK_SIZE));
>+          LOG(PR_LOG_DEBUG, ("Released block %d (trimming cache)",
>+              destinationBlockIndex));
>           FreeBlock(destinationBlockIndex);
>         }
>         // Free the overflowing block even if the copy failed.
>-        if (block->mClass != FREE_BLOCK) {
>-          LOG(PR_LOG_DEBUG, ("Released block %d from stream %p block %d(%lld) (trimming cache)",
>-              blockIndex, block->mStream, block->mStreamBlock,
>-              (long long)block->mStreamBlock*BLOCK_SIZE));
>-          FreeBlock(blockIndex);
>-        }
>+        LOG(PR_LOG_DEBUG, ("Released block %d (trimming cache)",
>+            blockIndex));
>+        FreeBlock(blockIndex);
>       }
>     }
>   }
>   // Try chopping back the array of cache entries and the cache file.
>   Truncate();
> 
>   // Count the blocks allocated for readahead of non-seekable streams
>   // (these blocks can't be freed but we don't want them to monopolize the
>@@ -1140,116 +1198,117 @@ nsMediaCache::QueueUpdate()
> 
> #ifdef DEBUG_VERIFY_CACHE
> void
> nsMediaCache::Verify()
> {
>   PR_ASSERT_CURRENT_THREAD_IN_MONITOR(mMonitor);
> 
>   mFreeBlocks.Verify();
>-  mPlayedBlocks.Verify();
>-  mMetadataBlocks.Verify();
>   for (PRUint32 i = 0; i < mStreams.Length(); ++i) {
>     nsMediaCacheStream* stream = mStreams[i];
>     stream->mReadaheadBlocks.Verify();
>-    if (!stream->mReadaheadBlocks.IsEmpty()) {
>-      // Verify that the readahead blocks are listed in stream block order
>-      PRInt32 block = stream->mReadaheadBlocks.GetFirstBlock();
>-      PRInt32 lastStreamBlock = -1;
>-      do {
>-        NS_ASSERTION(mIndex[block].mStream == stream, "Bad stream");
>-        NS_ASSERTION(lastStreamBlock < PRInt32(mIndex[block].mStreamBlock),
>-                     "Blocks not increasing in readahead stream");
>-        lastStreamBlock = PRInt32(mIndex[block].mStreamBlock);
>-        block = stream->mReadaheadBlocks.GetNextBlock(block);
>-      } while (block >= 0);
>+    stream->mPlayedBlocks.Verify();
>+    stream->mMetadataBlocks.Verify();
>+
>+    // Verify that the readahead blocks are listed in stream block order
>+    PRInt32 block = stream->mReadaheadBlocks.GetFirstBlock();
>+    PRInt32 lastStreamBlock = -1;
>+    while (block >= 0) {
>+      PRUint32 j = 0;
>+      while (mIndex[block].mOwners[j].mStream != stream) {
>+        ++j;
>+      }
>+      PRInt32 nextStreamBlock =
>+        PRInt32(mIndex[block].mOwners[j].mStreamBlock);
>+      NS_ASSERTION(lastStreamBlock < nextStreamBlock,
>+                   "Blocks not increasing in readahead stream");
>+      lastStreamBlock = nextStreamBlock;
>+      block = stream->mReadaheadBlocks.GetNextBlock(block);
>     }
>   }
> }
> #endif
> 
> void
>-nsMediaCache::InsertReadaheadBlock(PRInt32 aBlockIndex)
>+nsMediaCache::InsertReadaheadBlock(BlockOwner* aBlockOwner,
>+                                   PRInt32 aBlockIndex)
> {
>   PR_ASSERT_CURRENT_THREAD_IN_MONITOR(mMonitor);
> 
>-  Block* block = &mIndex[aBlockIndex];
>-  nsMediaCacheStream* stream = block->mStream;
>-  if (stream->mReadaheadBlocks.IsEmpty()) {
>-    stream->mReadaheadBlocks.AddFirstBlock(aBlockIndex);
>-    return;
>-  }
>-
>   // Find the last block whose stream block is before aBlockIndex's
>   // stream block, and insert after it
>+  nsMediaCacheStream* stream = aBlockOwner->mStream;
>   PRInt32 readaheadIndex = stream->mReadaheadBlocks.GetLastBlock();
>-  do {
>-    if (mIndex[readaheadIndex].mStreamBlock < block->mStreamBlock) {
>+  while (readaheadIndex >= 0) {
>+    BlockOwner* bo = GetBlockOwner(readaheadIndex, stream);
>+    NS_ASSERTION(bo, "stream must own its blocks");
>+    if (bo->mStreamBlock < aBlockOwner->mStreamBlock) {
>       stream->mReadaheadBlocks.AddAfter(aBlockIndex, readaheadIndex);
>       return;
>     }
>-    NS_ASSERTION(mIndex[readaheadIndex].mStreamBlock > block->mStreamBlock,
>+    NS_ASSERTION(bo->mStreamBlock > aBlockOwner->mStreamBlock,
>                  "Duplicated blocks??");
>     readaheadIndex = stream->mReadaheadBlocks.GetPrevBlock(readaheadIndex);
>-  } while (readaheadIndex >= 0);
>+  }
>+
>   stream->mReadaheadBlocks.AddFirstBlock(aBlockIndex);
>   Verify();
> }
> 
> void
> nsMediaCache::AllocateAndWriteBlock(nsMediaCacheStream* aStream, const void* aData,
>                                     nsMediaCacheStream::ReadMode aMode)
> {
>   PR_ASSERT_CURRENT_THREAD_IN_MONITOR(mMonitor);
> 
>   PRInt32 streamBlockIndex = aStream->mChannelOffset/BLOCK_SIZE;
>   // Extend the mBlocks array as necessary
>   while (streamBlockIndex >= PRInt32(aStream->mBlocks.Length())) {
>     aStream->mBlocks.AppendElement(-1);
>   }
>   if (aStream->mBlocks[streamBlockIndex] >= 0) {
>-    // Release the existing cache entry for this stream block
>+    // We no longer want to own this block
>     PRInt32 globalBlockIndex = aStream->mBlocks[streamBlockIndex];
>     LOG(PR_LOG_DEBUG, ("Released block %d from stream %p block %d(%lld)",
>         globalBlockIndex, aStream, streamBlockIndex, (long long)streamBlockIndex*BLOCK_SIZE));
>-    FreeBlock(globalBlockIndex);
>+    RemoveBlockOwner(globalBlockIndex, aStream);
>   }
> 
>   TimeStamp now = TimeStamp::Now();
>   PRInt32 blockIndex = FindBlockForIncomingData(now, aStream);
>   if (blockIndex >= 0) {
>-    Block* block = &mIndex[blockIndex];
>-    if (block->mClass != FREE_BLOCK) {
>-      LOG(PR_LOG_DEBUG, ("Released block %d from stream %p block %d(%lld)",
>-          blockIndex, block->mStream, block->mStreamBlock, (long long)block->mStreamBlock*BLOCK_SIZE));
>-      FreeBlock(blockIndex);
>-    }
>-    NS_ASSERTION(block->mClass == FREE_BLOCK, "Block should be free now!");
>+    FreeBlock(blockIndex);
> 
>+    Block* block = &mIndex[blockIndex];    
>     LOG(PR_LOG_DEBUG, ("Allocated block %d to stream %p block %d(%lld)",
>         blockIndex, aStream, streamBlockIndex, (long long)streamBlockIndex*BLOCK_SIZE));
>-    block->mStream = aStream;
>-    block->mStreamBlock = streamBlockIndex;
>-    block->mLastUseTime = now;
>+    BlockOwner* bo = block->mOwners.AppendElement();
>+    if (!bo)
>+      return;
>+
>+    bo->mStream = aStream;
>+    bo->mStreamBlock = streamBlockIndex;
>+    bo->mLastUseTime = now;
>     aStream->mBlocks[streamBlockIndex] = blockIndex;
>     mFreeBlocks.RemoveBlock(blockIndex);
>     if (streamBlockIndex*BLOCK_SIZE < aStream->mStreamOffset) {
>-      block->mClass = aMode == nsMediaCacheStream::MODE_PLAYBACK
>+      bo->mClass = aMode == nsMediaCacheStream::MODE_PLAYBACK
>         ? PLAYED_BLOCK : METADATA_BLOCK;
>       // This must be the most-recently-used block, since we
>       // marked it as used now (which may be slightly bogus, but we'll
>       // treat it as used for simplicity).
>-      GetListForBlock(block)->AddFirstBlock(blockIndex);
>+      GetListForBlock(bo)->AddFirstBlock(blockIndex);
>       Verify();
>     } else {
>       // This may not be the latest readahead block, although it usually
>       // will be. We may have to scan for the right place to insert
>       // the block in the list.
>-      block->mClass = READAHEAD_BLOCK;
>-      InsertReadaheadBlock(blockIndex);
>+      bo->mClass = READAHEAD_BLOCK;
>+      InsertReadaheadBlock(bo, blockIndex);
>     }
> 
>     nsresult rv = WriteCacheFile(blockIndex*BLOCK_SIZE, aData, BLOCK_SIZE);
>     if (NS_FAILED(rv)) {
>       LOG(PR_LOG_DEBUG, ("Released block %d from stream %p block %d(%lld)",
>           blockIndex, aStream, streamBlockIndex, (long long)streamBlockIndex*BLOCK_SIZE));
>       FreeBlock(blockIndex);
>     }
>@@ -1287,71 +1346,71 @@ nsMediaCache::ReleaseStreamBlocks(nsMedi
>   // is cached, but the only easy alternative is to scan the entire cache
>   // which isn't better
>   PRUint32 length = aStream->mBlocks.Length();
>   for (PRUint32 i = 0; i < length; ++i) {
>     PRInt32 blockIndex = aStream->mBlocks[i];
>     if (blockIndex >= 0) {
>       LOG(PR_LOG_DEBUG, ("Released block %d from stream %p block %d(%lld)",
>           blockIndex, aStream, i, (long long)i*BLOCK_SIZE));
>-      FreeBlock(blockIndex);
>+      RemoveBlockOwner(blockIndex, aStream);
>     }
>   }
> }
> 
> void
> nsMediaCache::Truncate()
> {
>   PRUint32 end;
>   for (end = mIndex.Length(); end > 0; --end) {
>-    if (mIndex[end - 1].mStream)
>+    if (!IsBlockFree(end - 1))
>       break;
>     mFreeBlocks.RemoveBlock(end - 1);
>   }
> 
>   if (end < mIndex.Length()) {
>     mIndex.TruncateLength(end);
>     // XXX We could truncate the cache file here, but we don't seem
>     // to have a cross-platform API for doing that. At least when all
>     // streams are closed we shut down the cache, which erases the
>     // file at that point.
>   }
> }
> 
> void
>-nsMediaCache::NoteBlockUsage(PRInt32 aBlockIndex,
>+nsMediaCache::NoteBlockUsage(nsMediaCacheStream* aStream, PRInt32 aBlockIndex,
>                              nsMediaCacheStream::ReadMode aMode,
>                              TimeStamp aNow)
> {
>   PR_ASSERT_CURRENT_THREAD_IN_MONITOR(mMonitor);
> 
>   if (aBlockIndex < 0) {
>     // this block is not in the cache yet
>     return;
>   }
> 
>-  Block* block = &mIndex[aBlockIndex];
>-  if (block->mClass == FREE_BLOCK) {
>+  BlockOwner* bo = GetBlockOwner(aBlockIndex, aStream);
>+  if (!bo) {
>     // this block is not in the cache yet
>     return;
>   }
> 
>   // The following check has to be <= because the stream offset has
>   // not yet been updated for the data read from this block
>-  NS_ASSERTION(block->mStreamBlock*BLOCK_SIZE <= block->mStream->mStreamOffset,
>+  NS_ASSERTION(bo->mStreamBlock*BLOCK_SIZE <= bo->mStream->mStreamOffset,
>                "Using a block that's behind the read position?");
> 
>-  GetListForBlock(block)->RemoveBlock(aBlockIndex);
>-  block->mClass =
>-    (aMode == nsMediaCacheStream::MODE_METADATA || block->mClass == METADATA_BLOCK)
>+  GetListForBlock(bo)->RemoveBlock(aBlockIndex);
>+  bo->mClass =
>+    (aMode == nsMediaCacheStream::MODE_METADATA || bo->mClass == METADATA_BLOCK)
>     ? METADATA_BLOCK : PLAYED_BLOCK;
>   // Since this is just being used now, it can definitely be at the front
>   // of mMetadataBlocks or mPlayedBlocks
>-  GetListForBlock(block)->AddFirstBlock(aBlockIndex);
>-  block->mLastUseTime = aNow;
>+  GetListForBlock(bo)->AddFirstBlock(aBlockIndex);
>+  bo->mLastUseTime = aNow;
>   Verify();
> }
> 
> void
> nsMediaCache::NoteSeek(nsMediaCacheStream* aStream, PRInt64 aOldOffset)
> {
>   PR_ASSERT_CURRENT_THREAD_IN_MONITOR(mMonitor);
> 
>@@ -1364,42 +1423,43 @@ nsMediaCache::NoteSeek(nsMediaCacheStrea
>       PR_MIN((aStream->mStreamOffset + BLOCK_SIZE - 1)/BLOCK_SIZE,
>              aStream->mBlocks.Length());
>     TimeStamp now = TimeStamp::Now();
>     while (blockIndex < endIndex) {
>       PRInt32 cacheBlockIndex = aStream->mBlocks[blockIndex];
>       if (cacheBlockIndex >= 0) {
>         // Marking the block used may not be exactly what we want but
>         // it's simple
>-        NoteBlockUsage(cacheBlockIndex, nsMediaCacheStream::MODE_PLAYBACK,
>+        NoteBlockUsage(aStream, cacheBlockIndex, nsMediaCacheStream::MODE_PLAYBACK,
>                        now);
>       }
>       ++blockIndex;
>     }
>   } else {
>     // We seeked backward. Convert from played to readahead.
>     // Any played block that is entirely after the start of the seeked-over
>     // range must be converted.
>     PRInt32 blockIndex =
>       (aStream->mStreamOffset + BLOCK_SIZE - 1)/BLOCK_SIZE;
>     PRInt32 endIndex =
>       PR_MIN((aOldOffset + BLOCK_SIZE - 1)/BLOCK_SIZE,
>              aStream->mBlocks.Length());
>     while (blockIndex < endIndex) {
>       PRInt32 cacheBlockIndex = aStream->mBlocks[endIndex - 1];
>       if (cacheBlockIndex >= 0) {
>-        Block* block = &mIndex[cacheBlockIndex];
>-        if (block->mClass != METADATA_BLOCK) {
>-          mPlayedBlocks.RemoveBlock(cacheBlockIndex);
>-          block->mClass = READAHEAD_BLOCK;
>+        BlockOwner* bo = GetBlockOwner(cacheBlockIndex, aStream);
>+        NS_ASSERTION(bo, "Stream doesn't own its blocks?");
>+        if (bo->mClass == PLAYED_BLOCK) {
>+          aStream->mPlayedBlocks.RemoveBlock(cacheBlockIndex);
>+          bo->mClass = READAHEAD_BLOCK;
>           // Adding this as the first block is sure to be OK since
>           // this must currently be the earliest readahead block
>           // (that's why we're proceeding backwards from the end of
>           // the seeked range to the start)
>-          GetListForBlock(block)->AddFirstBlock(cacheBlockIndex);
>+          aStream->mReadaheadBlocks.AddFirstBlock(cacheBlockIndex);
>           Verify();
>         }
>       }
>       --endIndex;
>     }
>   }
> }
> 
>@@ -1826,17 +1886,17 @@ nsMediaCacheStream::Read(char* aBuffer, 
>       // use it rather than waiting for the block to fill and land in
>       // the cache.
>       bytes = PR_MIN(size, mChannelOffset - mStreamOffset);
>       memcpy(aBuffer + count,
>         reinterpret_cast<char*>(mPartialBlockBuffer) + offsetInStreamBlock, bytes);
>       if (mCurrentMode == MODE_METADATA) {
>         mMetadataInPartialBlockBuffer = PR_TRUE;
>       }
>-      gMediaCache->NoteBlockUsage(cacheBlock, mCurrentMode, TimeStamp::Now());
>+      gMediaCache->NoteBlockUsage(this, cacheBlock, mCurrentMode, TimeStamp::Now());
>     } else {
>       if (cacheBlock < 0) {
>         if (count > 0) {
>           // Some data has been read, so return what we've got instead of
>           // blocking
>           break;
>         }
> 
>@@ -1845,17 +1905,17 @@ nsMediaCacheStream::Read(char* aBuffer, 
>         if (mClosed) {
>           // We may have successfully read some data, but let's just throw
>           // that out.
>           return NS_ERROR_FAILURE;
>         }
>         continue;
>       }
> 
>-      gMediaCache->NoteBlockUsage(cacheBlock, mCurrentMode, TimeStamp::Now());
>+      gMediaCache->NoteBlockUsage(this, cacheBlock, mCurrentMode, TimeStamp::Now());
> 
>       PRInt64 offset = cacheBlock*BLOCK_SIZE + offsetInStreamBlock;
>       nsresult rv = gMediaCache->ReadCacheFile(offset, aBuffer + count, size, &bytes);
>       if (NS_FAILED(rv)) {
>         if (count == 0)
>           return rv;
>         // If we did successfully read some data, may as well return it
>         break;
>diff --git a/content/media/nsMediaCache.h b/content/media/nsMediaCache.h
>--- a/content/media/nsMediaCache.h
>+++ b/content/media/nsMediaCache.h
>@@ -431,16 +431,20 @@ private:
>   PRInt64           mStreamLength;
>   // For each block in the stream data, maps to the cache entry for the
>   // block, or -1 if the block is not cached.
>   nsTArray<PRInt32> mBlocks;
>   // The list of read-ahead blocks, ordered by stream offset; the first
>   // block is the earliest in the stream (so the last block will be the
>   // least valuable).
>   BlockList         mReadaheadBlocks;
>+  // The list of metadata blocks; the first block is the most recently used
>+  BlockList         mMetadataBlocks;
>+  // The list of played-back blocks; the first block is the most recently used
>+  BlockList         mPlayedBlocks;
>   // The last reported estimate of the decoder's playback rate
>   PRUint32          mPlaybackBytesPerSecond;
>   // The number of times this stream has been Pinned without a
>   // corresponding Unpin
>   PRUint32          mPinCount;
>   // The last reported read mode
>   ReadMode          mCurrentMode;
>   // Set to true when the stream has been closed either explicitly or

Comment 25

[cajbir (:cajbir)]

Comment on attachment 400676 [details] [diff] [review]
Part 8: Actually support cache stream cloning

># HG changeset patch
># User Robert O'Callahan <[e-mail]>
># Date 1252981844 -43200
># Node ID eec02dd2c9954a5f7e2664b9e652c73117c70f28
># Parent  d7cdd8e1b04122047255fd7433f3a7b4cd060895
>Bug 513144. Make nsMediaChannelStream::CloneData clone the underlying cache stream, which adds the new stream as co-owner of all the nsMediaCache blocks currently cached for the original stream. Also, use NS_NEW_RUNNABLE_METHOD instead of the SuspendedStatusChanged class. r=doublec
>
>diff --git a/content/media/nsMediaCache.cpp b/content/media/nsMediaCache.cpp
>--- a/content/media/nsMediaCache.cpp
>+++ b/content/media/nsMediaCache.cpp
>@@ -154,16 +154,19 @@ public:
>   // Notify the cache that a block has been read from. This is used
>   // to update last-use times. The block may not actually have a
>   // cache entry yet since Read can read data from a stream's
>   // in-memory mPartialBlockBuffer while the block is only partly full,
>   // and thus hasn't yet been committed to the cache. The caller will
>   // call QueueUpdate().
>   void NoteBlockUsage(nsMediaCacheStream* aStream, PRInt32 aBlockIndex,
>                       nsMediaCacheStream::ReadMode aMode, TimeStamp aNow);
>+  // Mark aStream as having the block, adding it as an owner.
>+  void AddBlockOwnerAsReadahead(PRInt32 aBlockIndex, nsMediaCacheStream* aStream,
>+                                PRInt32 aStreamBlockIndex);
> 
>   // This queues a call to Update() on the main thread.
>   void QueueUpdate();
> 
>   // Updates the cache state asynchronously on the main thread:
>   // -- try to trim the cache back to its desired size, if necessary
>   // -- suspend channels that are going to read data that's lower priority
>   // than anything currently cached
>@@ -836,16 +839,33 @@ nsMediaCache::RemoveBlockOwner(PRInt32 a
>         mFreeBlocks.AddFirstBlock(aBlockIndex);
>       }
>       return;
>     }
>   }
> }
> 
> void
>+nsMediaCache::AddBlockOwnerAsReadahead(PRInt32 aBlockIndex,
>+                                       nsMediaCacheStream* aStream,
>+                                       PRInt32 aStreamBlockIndex)
>+{
>+  Block* block = &mIndex[aBlockIndex];
>+  if (block->mOwners.IsEmpty()) {
>+    mFreeBlocks.RemoveBlock(aBlockIndex);
>+  }
>+  BlockOwner* bo = block->mOwners.AppendElement();
>+  bo->mStream = aStream;
>+  bo->mStreamBlock = aStreamBlockIndex;
>+  aStream->mBlocks[aStreamBlockIndex] = aBlockIndex;
>+  bo->mClass = READAHEAD_BLOCK;
>+  InsertReadaheadBlock(bo, aBlockIndex);
>+}
>+
>+void
> nsMediaCache::FreeBlock(PRInt32 aBlock)
> {
>   PR_ASSERT_CURRENT_THREAD_IN_MONITOR(mMonitor);
> 
>   Block* block = &mIndex[aBlock];
>   if (block->mOwners.IsEmpty()) {
>     // already free
>     return;
>@@ -1991,14 +2011,49 @@ nsMediaCacheStream::ReadFromCache(char* 
>   return NS_OK;
> }
> 
> nsresult
> nsMediaCacheStream::Init()
> {
>   NS_ASSERTION(NS_IsMainThread(), "Only call on main thread");
> 
>+  if (mInitialized)
>+    return NS_OK;
>+
>   InitMediaCache();
>   if (!gMediaCache)
>     return NS_ERROR_FAILURE;
>   gMediaCache->OpenStream(this);
>+  mInitialized = PR_TRUE;
>   return NS_OK;
> }
>+
>+nsresult
>+nsMediaCacheStream::InitAsClone(nsMediaCacheStream* aOriginal)
>+{
>+  if (mInitialized)
>+    return NS_OK;
>+
>+  nsresult rv = Init();
>+  if (NS_FAILED(rv))
>+    return rv;
>+
>+  // Grab cache blocks from aOriginal as readahead blocks for our stream
>+  nsAutoMonitor mon(gMediaCache->Monitor());
>+
>+  mPrincipal = aOriginal->mPrincipal;
>+  mStreamLength = aOriginal->mStreamLength;
>+  mIsSeekable = aOriginal->mIsSeekable;
>+
>+  for (PRUint32 i = 0; i < aOriginal->mBlocks.Length(); ++i) {
>+    PRInt32 cacheBlockIndex = aOriginal->mBlocks[i];
>+    if (cacheBlockIndex < 0)
>+      continue;
>+
>+    while (i >= mBlocks.Length()) {
>+      mBlocks.AppendElement(-1);
>+    }
>+    gMediaCache->AddBlockOwnerAsReadahead(cacheBlockIndex, this, i);
>+  }
>+
>+  return NS_OK;
>+}
>diff --git a/content/media/nsMediaCache.h b/content/media/nsMediaCache.h
>--- a/content/media/nsMediaCache.h
>+++ b/content/media/nsMediaCache.h
>@@ -217,27 +217,34 @@ public:
>     MODE_PLAYBACK
>   };
> 
>   // aClient provides the underlying transport that cache will use to read
>   // data for this stream.
>   nsMediaCacheStream(nsMediaChannelStream* aClient)
>     : mClient(aClient), mChannelOffset(0),
>       mStreamOffset(0), mStreamLength(-1), mPlaybackBytesPerSecond(10000),
>-      mPinCount(0), mCurrentMode(MODE_PLAYBACK), mClosed(PR_FALSE),
>+      mPinCount(0), mCurrentMode(MODE_PLAYBACK),
>+      mInitialized(PR_FALSE), mClosed(PR_FALSE),
>       mIsSeekable(PR_FALSE), mCacheSuspended(PR_FALSE),
>       mMetadataInPartialBlockBuffer(PR_FALSE),
>       mUsingNullPrincipal(PR_FALSE) {}
>   ~nsMediaCacheStream();
> 
>-  // Set up this stream with the cache. Can fail on OOM. Must be called
>-  // before other methods on this object; no other methods may be called
>-  // if this fails.
>+  // Set up this stream with the cache. Can fail on OOM. One
>+  // of InitAsClone or Init must be called before any other method on
>+  // this class. Does nothing if already initialized.
>   nsresult Init();
> 
>+  // Set up this stream with the cache, assuming it's for the same data
>+  // as the aOriginal stream. Can fail on OOM. Exactly one
>+  // of InitAsClone or Init must be called before any other method on
>+  // this class. Does nothing if already initialized.
>+  nsresult InitAsClone(nsMediaCacheStream* aOriginal);
>+
>   // These are called on the main thread.
>   // Tell us whether the stream is seekable or not. Non-seekable streams
>   // will always pass 0 for aOffset to CacheClientSeek. This should only
>   // be called while the stream is at channel offset 0. Seekability can
>   // change during the lifetime of the nsMediaCacheStream --- every time
>   // we do an HTTP load the seekability may be different (and sometimes
>   // is, in practice, due to the effects of caching proxies).
>   void SetSeekable(PRBool aIsSeekable);
>@@ -442,16 +449,18 @@ private:
>   BlockList         mPlayedBlocks;
>   // The last reported estimate of the decoder's playback rate
>   PRUint32          mPlaybackBytesPerSecond;
>   // The number of times this stream has been Pinned without a
>   // corresponding Unpin
>   PRUint32          mPinCount;
>   // The last reported read mode
>   ReadMode          mCurrentMode;
>+  // Set to true when Init or InitAsClone has been called
>+  PRPackedBool      mInitialized;
>   // Set to true when the stream has been closed either explicitly or
>   // due to an internal cache error
>   PRPackedBool      mClosed;
>   // The last reported seekability state for the underlying channel
>   PRPackedBool      mIsSeekable;
>   // true if the cache has suspended our channel because the cache is
>   // full and the priority of the data that would be received is lower
>   // than the priority of the data already in the cache
>diff --git a/content/media/nsMediaStream.cpp b/content/media/nsMediaStream.cpp
>--- a/content/media/nsMediaStream.cpp
>+++ b/content/media/nsMediaStream.cpp
>@@ -447,17 +447,17 @@ already_AddRefed<nsIPrincipal> nsMediaCh
> 
> nsMediaStream* nsMediaChannelStream::CloneData(nsMediaDecoder* aDecoder)
> {
>   NS_ASSERTION(NS_IsMainThread(), "Only call on main thread");
> 
>   nsMediaChannelStream* stream = new nsMediaChannelStream(aDecoder, nsnull, mURI);
>   if (stream) {
>     stream->RecreateChannel();
>-    // XXXroc need to clone mCacheStream's data here
>+    stream->mCacheStream.InitAsClone(&mCacheStream);
>   }
>   return stream;
> }
> 
> void nsMediaChannelStream::CloseChannel()
> {
>   NS_ASSERTION(NS_IsMainThread(), "Only call on main thread");
> 
>@@ -609,68 +609,48 @@ nsMediaChannelStream::CacheClientSeek(PR
>   nsresult rv = RecreateChannel();
>   if (NS_FAILED(rv))
>     return rv;
> 
>   mOffset = aOffset;
>   return OpenChannel(nsnull);
> }
> 
>-class SuspendedStatusChanged : public nsRunnable 
>-{
>-public:
>-  SuspendedStatusChanged(nsMediaDecoder* aDecoder) :
>-    mDecoder(aDecoder)
>-  {
>-    MOZ_COUNT_CTOR(SuspendedStatusChanged);
>-  }
>-  ~SuspendedStatusChanged()
>-  {
>-    MOZ_COUNT_DTOR(SuspendedStatusChanged);
>-  }
>-
>-  NS_IMETHOD Run() {
>-    mDecoder->NotifySuspendedStatusChanged();
>-    return NS_OK;
>-  }
>-
>-private:
>-  nsRefPtr<nsMediaDecoder> mDecoder;
>-};
>-
> nsresult
> nsMediaChannelStream::CacheClientSuspend()
> {
>   {
>     nsAutoLock lock(mLock);
>     ++mCacheSuspendCount;
>   }
>   Suspend(PR_FALSE);
> 
>   // We have to spawn an event here since we're being called back from
>   // a sensitive place in nsMediaCache, which doesn't want us to reenter
>   // the decoder and cause deadlocks or other unpleasantness
>-  nsCOMPtr<nsIRunnable> event = new SuspendedStatusChanged(mDecoder);
>+  nsCOMPtr<nsIRunnable> event =
>+    NS_NEW_RUNNABLE_METHOD(nsMediaDecoder, mDecoder, NotifySuspendedStatusChanged);
>   NS_DispatchToMainThread(event, NS_DISPATCH_NORMAL);
>   return NS_OK;
> }
> 
> nsresult
> nsMediaChannelStream::CacheClientResume()
> {
>   Resume();
>   {
>     nsAutoLock lock(mLock);
>     --mCacheSuspendCount;
>   }
> 
>   // We have to spawn an event here since we're being called back from
>   // a sensitive place in nsMediaCache, which doesn't want us to reenter
>   // the decoder and cause deadlocks or other unpleasantness
>-  nsCOMPtr<nsIRunnable> event = new SuspendedStatusChanged(mDecoder);
>+  nsCOMPtr<nsIRunnable> event =
>+    NS_NEW_RUNNABLE_METHOD(nsMediaDecoder, mDecoder, NotifySuspendedStatusChanged);
>   NS_DispatchToMainThread(event, NS_DISPATCH_NORMAL);
>   return NS_OK;
> }
> 
> PRInt64
> nsMediaChannelStream::GetNextCachedData(PRInt64 aOffset)
> {
>   return mCacheStream.GetNextCachedData(aOffset);

Comment 26

[cajbir (:cajbir)]

Oops, ignore those last couple of comments :)

Comment 27

[Robert O'Callahan (:roc) (email my personal email if necessary)]

http://hg.mozilla.org/mozilla-central/rev/c71eb3c6822c
http://hg.mozilla.org/mozilla-central/rev/4b57fb834419
http://hg.mozilla.org/mozilla-central/rev/3cdab1fac583
http://hg.mozilla.org/mozilla-central/rev/969304e8f61f
http://hg.mozilla.org/mozilla-central/rev/c4bca0456beb
http://hg.mozilla.org/mozilla-central/rev/857725884e1e
http://hg.mozilla.org/mozilla-central/rev/a4ef15912d21
http://hg.mozilla.org/mozilla-central/rev/aea350f32388
http://hg.mozilla.org/mozilla-central/rev/643b222c2d83
http://hg.mozilla.org/mozilla-central/rev/0fd888645cf3

Comment 28

[Robert O'Callahan (:roc) (email my personal email if necessary)]

This landing exposed some more existing bugs which triggered test failures involving the Wave decoder not reporting HAVE_CURRENT_DATA in the ended state. Bug 517818 has patches to fix those issues.

Comment 29

[Robert O'Callahan (:roc) (email my personal email if necessary)]

http://hg.mozilla.org/releases/mozilla-1.9.2/rev/fa9bfea418c7
http://hg.mozilla.org/releases/mozilla-1.9.2/rev/3bb3a9af2e9d
http://hg.mozilla.org/releases/mozilla-1.9.2/rev/7589ace447e4
http://hg.mozilla.org/releases/mozilla-1.9.2/rev/c306bf87ce40
http://hg.mozilla.org/releases/mozilla-1.9.2/rev/537912798fa7
http://hg.mozilla.org/releases/mozilla-1.9.2/rev/b28253c7ad68
http://hg.mozilla.org/releases/mozilla-1.9.2/rev/39ccb1720610
http://hg.mozilla.org/releases/mozilla-1.9.2/rev/d161112508a1
http://hg.mozilla.org/releases/mozilla-1.9.2/rev/e947227aad68
http://hg.mozilla.org/releases/mozilla-1.9.2/rev/abc093d8f8f5

Comment 30

[Eric Shepherd [:sheppy]]

Now documented here:

https://developer.mozilla.org/En/NsIDOMHTMLMediaElement#mozLoadFrom%28%29