956997 - Media Recording - Pass timeslices value from recorder to encoder writer

Status: RESOLVED WONTFIX

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

Description

[Randy Lin [:rlin] - Be Mozillian on 2015/01/26]

We have fragment mp4 muxer implementation and we can sync the fragment duration as same as timeslices value from start method.

Comment 1

[Randy Lin [:rlin] - Be Mozillian on 2015/01/26]

Hi Alfredo, 
Please help this, thanks.

Comment 2

[Alfredo Yang (:alfredo)]

Hi Chris,

From spec [2], 'timeslice' is 'the number of milliseconds of data to return in a single Blob.'
But current implementation in [1] returns the blob for every 'timeslice' milliseconds. If my understanding is correct, it should be muxer, not MediaRecorder to decide 'timeslice' of blob because only muxer knows the time length of blob, is that correct?

[1] http://dxr.mozilla.org/mozilla-central/source/content/media/MediaRecorder.cpp#286
[2] https://dvcs.w3.org/hg/dap/raw-file/tip/media-stream-capture/MediaRecorder.html

Comment 3

[Chris Pearce [:cpearce (Not reading bugmail)]]

I don't know the MediaRecorder API very well, so just looking at it now here's my guess:

I think mTimeSlice is being used wrong in MediaRecoder::Session. I think mTimeSlice should be the duration of a blob produced by the muxer, not the time duration in between a dataavailable event being dispatched.

if ((TimeStamp::Now() - mLastBlobTimeStamp).ToMilliseconds() > mTimeSlice) is true, that does not mean that mTimeSlice milliseconds of data has been appended to the encoded buffer cache, right? Data could be late.

It seems to me that mTimeSlice should be being passed to the muxer, and it should be using that as its fragment duration if possible, and once you have a full fragment you should then be dispatching it to JavaScript.

I don't know this code very well, I may be wrong, but that's my interpretation.

Comment 4

[Randy Lin [:rlin] - Be Mozillian on 2015/01/26]

Ya, I also think the time-slice should be duration of the blob, not the blob push out interval.
My implementation just consider the realtime case, so it should be a problem if we allow to record a offline media stream).

Comment 5

[Alfredo Yang (:alfredo)]

Attachment: media_recorder_timeslice

wip for MediaRecorder and ISOMediaWriter.

Comment 6

[Alfredo Yang (:alfredo)]

Attachment: media_recorder_timeslice

Remove the mechanism for counting the timeslice by current time in MediaRecorder::Session so the blob duration is decided by encoder or muxer.

Comment 7

[Alfredo Yang (:alfredo)]

Attachment: media_recorder_timeslice_iso_container

Comment 8

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

I actually think this doesn't matter much and that the current code is fine. There was never supposed to be a hard guarantee that the data in the blob will have the requested duration. Using the timer should work fine for the use-cases I can think of. Does setting the fragment duration in the ISOMediaWriter actually provide any benefits to the author?

Comment 9

[Alfredo Yang (:alfredo)]

I can't think any benefit to JS author in this case. I'll keep the original implementation.
Thanks for feedback.

Comment 10

[Randy Lin [:rlin] - Be Mozillian on 2015/01/26]

Refer to comment 8, We don't need to implement this function at this time. Close this bug at this time.