1098990 - Trun segments don't necessarily contain contiguous samples

Status: RESOLVED FIXED

(Core :: Audio/Video, defect)

Description

[Matt Woodrow (:mattwoodrow)]

This happens with the 'Microsoft #2' video on the dashif player.

The trun box for this file has the sample-composition-time-offsets-present flag present, so each sample has essentially arbitrary composition time.

We end up with a collection of samples for the 0-2 second range, and a bunch around 429 seconds.

Index dump: http://pastebin.mozilla.org/7297431

Our MoofParser code assumes that all the samples must be contiguous, so it edits them to make this true at [1]. Sample 47 in the dump is ~427 seconds long because of this editing.

MP4Demuxer also assumes this, so we use the time range for the Moof rather than adding up the individual samples in the index [2]. We need to fix both of these for buffered range calculations to be correct.

I can't see anything in the spec that would require the samples to be contiguous, anyone know why we assume this?


[1] http://mxr.mozilla.org/mozilla-central/source/media/libstagefright/binding/MoofParser.cpp#224
[2] http://mxr.mozilla.org/mozilla-central/source/media/libstagefright/binding/Index.cpp#156

Comment 1

[Matt Woodrow (:mattwoodrow)]

Note that there only appears to be one track for this video.

Comment 2

[Matt Woodrow (:mattwoodrow)]

Attachment: cts is signed in version 1

For boxes that inherit from 'FullBox', the flags field is only 24bits and the top 8 bits are the version.

In version 1 of a 'trun' box, the cts offset it to be parsed as signed rather than unsigned.

Comment 3

[Anthony Jones (:ajones, :kentuckyfriedtakahe, :k17e)]

Comment on attachment 8523573 [details] [diff] [review]
cts is signed in version 1

Review of attachment 8523573 [details] [diff] [review]:
-----------------------------------------------------------------

::: media/libstagefright/binding/MoofParser.cpp
@@ +199,5 @@
> +    if (flags & 0x800) {
> +      if (version == 0) {
> +        ctsOffset = reader->ReadU32();
> +      } else {
> +        ctsOffset = (int32_t)reader->ReadU32();

Please add reader->Read32() to ByteReader rather than casting here.

Comment 4

[Matt Woodrow (:mattwoodrow)]

https://hg.mozilla.org/integration/mozilla-inbound/rev/5492e9dc06f1

Comment 5

[Carsten Book [:Tomcat]]

https://hg.mozilla.org/mozilla-central/rev/5492e9dc06f1