1275858 - MediaRecorder does not support switching tracks on the recording MediaStream

Status: NEW

(Core :: Audio/Video: Recording, defect, P4)

Description

[Rob Swain]

User Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_11_5) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/50.0.2661.102 Safari/537.36

Steps to reproduce:

I am testing some MediaRecorder functionality on FireFox Dev Edition 48.0a2 (2016-05-26) on OS X 10.11.5 using this https://jsfiddle.net/rshodaw8/9/

Run that fiddle and it will try to get one default resolution video stream and one 160x90 video stream. It then uses MediaRecorder to record the first stream for 5 seconds and then it swaps out the first video track with the second.


Actual results:

Aside from bug #1275856 , there is the fact that addition/removal of tracks to/from a recording media stream causes an error.


Expected results:

Added tracks are also recorded. Removed tracks stop being recorded. The resulting file might have individual and unique audio/video tracks for each of the tracks that were added, which is probably the most logical approach. Alternatively/additionally, if there is only one track each of audio / video at all times then these could remain as the 'default' audio / video tracks in the output file. However, one could argue that this would be inconsistent, it may be what the user actually wants to happen.

Comment 1

[Andreas Pehrson [:pehrsons]]

This would be nice to have, but is subject to a spec change. See [1]:

> ErrorEvent 	EventError
> An error has occurred, e.g. out of memory or a modification to the stream has
> occurred that makes it impossible to continue recording (e.g. a Track has been
> added to or removed from the said stream while recording is occurring).

A workaround for now for dynamic track changes is to compose them into the same track with canvas/WebAudio.


[1] http://w3c.github.io/mediacapture-record/MediaRecorder.html#event-summary

Comment 2

[Rob Swain]

Attachment: track-switch.html

This is an HTML/JS file to ease debugging. Apparently jsfiddle is difficult to work with.

Comment 3

[Bulk Bug Changes for mreavy's org]

Mass change P3->P4 to align with new Mozilla triage process.