1616175 - Allow MediaRecorder "stop" event dispatch when tracks end, even if still in MediaTrackGraph

Status: RESOLVED FIXED

(Core :: Audio/Video: Recording, defect, P2)

Description

[Karl Tomlinson (:karlt)]

https://searchfox.org/mozilla-central/rev/0439db3a39faddb90197a87cc184c57dcbf0a770/dom/media/encoder/MediaEncoder.h#102
says "When all input tracks end, the MediaEncoder will automatically stop and shut down."

That's true as far as the fact that MediaEncoder::Shutdown() gets called, but resolution of the promise it returns and EncoderListener::Shutdown() are blocked on MediaEncoder::AudioTrackListener::mShutdownPromise, which waits for removal of its MediaTrack from the graph.

For bug 1596655, I would like the MediaTrack for AudioDestinationNode to remain in the graph well after the track ends. The blocked EncoderListener shutdown means that the "stop" event is not dispatched to the MediaRecorder until the AudioDestinationNode is destroyed.

This appears to be a consequence of a change in behavior introduced in https://hg.mozilla.org/mozilla-central/rev/509719f98963a8f1c2663dac01279a734d30e71a

Comment 1

[Karl Tomlinson (:karlt)]

(In reply to Karl Tomlinson (:karlt) from comment #0)

That's true as far as the fact that MediaEncoder::Shutdown() gets called, but resolution of the promise it returns and EncoderListener::Shutdown() are blocked on MediaEncoder::AudioTrackListener::mShutdownPromise,

The first promise in the chain returned from MediaEncoder::Shutdown() is waiting for the listeners to be removed from their tracks.
Removal of listeners from tracks would be triggered from MediaEncoder::Stop() from MediaEncoder::Cancel() after Session::Shutdown() after Session::DoSessionEndTask() after Session::MediaEncoderShutdown() from Session::EncoderListener::Shutdown(), which is not called until the promise resolves.

Comment 2

[Karl Tomlinson (:karlt)]

Attachment: Bug 1616175 update function name in NotifyRemoved() doc r?padenot

Comment 3

[Karl Tomlinson (:karlt)]

Attachment: Bug 1616175 trigger track listener removal before waiting for removal r?bryce

IsShutdown() is replaced with a AssertShutdownCalled() because testing
mShutdownPromise would race if the timing of Shutdown() is not known.

Depends on D65066

Comment 4

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/3a0f667c0908
update function name in NotifyRemoved() doc r=padenot
https://hg.mozilla.org/integration/autoland/rev/9f768142ce40
trigger track listener removal before waiting for removal r=bryce

Comment 5

[Oana Pop-Rus]

https://hg.mozilla.org/mozilla-central/rev/3a0f667c0908
https://hg.mozilla.org/mozilla-central/rev/9f768142ce40