change audio track force clear of video buffer

[rounce]

When I change audio track via selectVariantTrack(track, true) shaka player clear audio AND video buffer

audio:
at shaka.media.StreamingEngine.clearBuffer_ (shaka-player/lib/media/streaming_engine.js:1762:5)
at shaka.media.StreamingEngine.switch (shaka-player/lib/media/streaming_engine.js:530:12)
at shaka.Player.deferredSwitch_ (js/shaka-player/lib/player.js:1714:35)
at shaka.Player.selectVariantTrack (js/shaka-player/lib/player.js:1125:8)

then video:
at shaka.media.StreamingEngine.clearBuffer_ (streaming_engine.js:1762)
at shaka.media.StreamingEngine.seeked (streaming_engine.js:604)
at shaka.Player.onSeek_ (player.js:1891)
at shaka.media.Playhead.onSeeking_ (playhead.js:514)

[TheModMaker]

A variant track represents a pair of both audio and video. So when you switch to a different variant, you are changing both audio and video streams, so we clear both buffers. In v2.1 (latest master), you can no longer select individual audio and video tracks, you can only select an audio/video pair.

[rounce]

Why remove useful functionality? I'm sure in many cases it's necessary for independent change of tracks. In my case it remains to make a fork or to use the previous version forever.

[ismena]

@rounce we had to introduce this change in order to be able to add support for HLS (the way HLS manifest is structured there is no way for us to know certain information about individual streams that is needed to operate on a stream level).
For DASH manifests we are creating variants for all possible audio+video combinations, so if you want to keep current video track, but change the audio you should be able to find the right variant track.
For a visual on how things work in the new world you can check out our nightly build demo page (under "info" section).

Sorry that this change complicated things for you. If you have a specific use case you're worried about, we'd be happy to advise on how to best accommodate it with v2.1 streaming logic if you do decide to upgrade.

[TheModMaker]

In HLS, we are only given audio/video pairs and those are what we can switch between. So if you wanted to switch to a different audio stream, it might not be compatible with the current video stream. This would mean that we would either have to throw an error for the change, ignore the change, or also switch video. These are not good user experiences, so we only allow changing by variants directly.

If all you want to do is change the audio language, there is a new API to do that. player.selectAudioLanguage will change the selected audio language and switch tracks for you. This will change the current audio track, trying to keep the video track the same.

[rounce]

selectAudioLanguage might be useful in some cases. But often I have several different audio tracks of one languarge. Thanks. I will make fork.

This would mean that we would either have to throw an error for the change, ignore the change, or also switch video

either add parameter to selectVariantTrack or change second parameter. Many options to keep the functionality, without disturbing the logic of hls.

[joeyparrish]

@rounce, you make a good point. It would seem at a glance that there's no reason you would have to clear audio when switching to a variant with the same audio stream. However, there are often strange implementation quirks in MSE on various browsers. We may be doing this to work around a browser bug.

We will re-evaluate.