1049302 - B2G audio+video captures cause major audio delay (regression)

Status: RESOLVED FIXED

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

Description

[Randell Jesup [:jesup] (needinfo me)]

At some point, audio+video captures got quite delayed (up to 800ms).  The value of delay is highly hardware dependent, so some devices will show very little delay - it depends on the camera used and the drivers.

Digging into the logs, I found the cause was the B2G camera refactor that made mState == kStarted happen only after the Camera hardware changes state.  This would seem innocuous, and it's still set before Start() returns - but we AddTrack first, and NotifyPull() has a early-bailout if mState != kStarted.  That means that the MSG's idea of time for the Video track isn't updated and stays at 0, causing the entire Stream to stall/block.

Really, this was a bit of over-reuse of the existing state structure to also mirror the hardware state and provide a 'return' value for camera start, but that's not worth worrying about.

Simply removing the early-exit solves it, and the test is actually just paranoia - everything is fine without it.  Very simple patch

Comment 1

[Randell Jesup [:jesup] (needinfo me)]

Attachment: Avoid audio delay in B2G audio-video getUserMedia captures

Comment 2

[Randell Jesup [:jesup] (needinfo me)]

https://hg.mozilla.org/integration/mozilla-inbound/rev/e9348984ca0e

Comment 3

[Randell Jesup [:jesup] (needinfo me)]

Comment on attachment 8468210 [details] [diff] [review]
Avoid audio delay in B2G audio-video getUserMedia captures

Note: already 2.0+

Approval Request Comment
[Feature/regressing bug #]:B2G camera refactor (fx31)

[User impact if declined]: audio+video getusermedia streams have hardware-dependent audio delay (up to 800ms).

[Describe test coverage new/current, TBPL]: requires manual testing; HW dependent

[Risks and why]: virtually no risk; removes a redundant "don't do this is we don't think we're running" test - but if MediaStreamGraph asks us for data, it still believes we're live and we need to provide it.

[String/UUID change made/needed]: none

Comment 4

[Lawrence Mandel [:lmandel] (use needinfo)]

Comment on attachment 8468210 [details] [diff] [review]
Avoid audio delay in B2G audio-video getUserMedia captures

B2G specific changes should land on m-c for 2.1 and b2g32 for 2.0. AFAICT there is no need to land this change on Aurora and Beta.

Comment 5

[Nigel Babu [:nigelb]]

https://hg.mozilla.org/mozilla-central/rev/e9348984ca0e

Comment 6

[Ryan VanderMeulen [:RyanVM]]

https://hg.mozilla.org/releases/mozilla-b2g32_v2_0/rev/7a9a80e71e12