YouTube currently serves AAC audio to Firefox users watching H.264 or VP9. YouTube serves Opus to Chrome users. Unfortunately, Firefox's MSE implementation only supports Opus paired with VP9. We would like to be able to play Opus regardless of video codec (or container?).

I'm not aware of such restrictions. I certainly see us being served webm with opus only content if I enable mediasource with webm. What make you think we don't support opus only webm ? from playing: https://www.youtube.com/watch?v=XqLTe8h0-jo 950272[118b06b40]: MediaSource(136f6f220)::AddSourceBuffer: AddSourceBuffer(aType=audio/webm; codecs="opus") followed by: 62935040[1006b8730]: TrackBuffersManager(11914a000:audio/webm)::ProcessFrames: Processing audio/webm; codecs=opus frame(pts:0 end:21000, dts:0, duration:21000, kf:1) 62935040[1006b8730]: TrackBuffersManager(11914a000:audio/webm)::ProcessFrames: Processing audio/webm; codecs=opus frame(pts:21000 end:41000, dts:21000, duration:20000, kf:1) The issue is youtube not serving us opus with h264, nothing to do with a limitation on our part. I don't even think the old MSE architecture ever had that limitation either.

oh I see what you mean. Our pref is for webm or mp4 ; we can't enable webm without also enabling vp9/vp8. We don't have anything available that would allow one without also enabling the other.

(In reply to Jean-Yves Avenard [:jya] from comment #1) > I certainly see us being served webm with opus only content if I enable > mediasource with webm. > > What make you think we don't support opus only webm ? That's what Anthony told me. :) > The issue is youtube not serving us opus with h264, nothing to do with a > limitation on our part. I don't know if YouTube actually serves H.264 + Opus. YouTube says they serve Opus to nearly all Chrome users and we know they prefer VP9 over H.264. They might only support VP9 + Opus. I can ask. If they don't, then maybe there is little need to fix this bug.

This adds a media.mediasource.webm.audio.enabled preference (true by default) to disable opus or vorbis audio in webm mediasource.

btw, YouTube says they serve Opus to nearly 100% of Chrome users. When we're ready, they can run A/B tests comparing Opus vs AAC for Firefox users.

Comment on attachment 8695176 [details] [diff] [review] [MSE] Allow webm/audio independently of video. Approval Request Comment [Feature/regressing bug #]: [User impact if declined]: YouTube users will continue to receive AAC, which is slightly lower quality audio than Opus. [Describe test coverage new/current, TreeHerder]: In Firefox 43, users without AAC platform decoders (e.g. 100% of Windows XP, 2% of other Windows versions, and 3% of Linux) already receive Opus as a fallback (bug 1217170). [Risks and why]: Medium risk, because we will be using the codec for more content with more users. However, YouTube can control whether they serve AAC or Opus on the server side. Uplifting this to Beta 44 will make it easier for YouTube to selectively A/B test Firefox's Opus vs AAC before enabling for our release users. [String/UUID change made/needed]: N/A

Comment on attachment 8695176 [details] [diff] [review] [MSE] Allow webm/audio independently of video. Taking it, Beta44+