Does v3 Google Cast receiver parse alternative audio tracks from an hls master playlist automatically or do I have to define them in the sender?

问题

I'm trying to get a multi-audio HLS stream working on a v3 Google Cast custom receiver app. The master playlist of the stream refers to several video renditions of different resolution and two alternative audio tracks:

#EXTM3U
#EXT-X-MEDIA:TYPE=AUDIO,GROUP-ID="aac",LANGUAGE="de",NAME="TV Ton",DEFAULT=YES, AUTOSELECT=YES,URI="index_1_a.m3u8"
#EXT-X-MEDIA:TYPE=AUDIO,GROUP-ID="aac",LANGUAGE="de",NAME="Audiodeskription",DEFAULT=NO, AUTOSELECT=NO,URI="index_2_a.m3u8"
#EXT-X-STREAM-INF:AUDIO="aac",BANDWIDTH=383000,RESOLUTION=320x176,CODECS="avc1.4d001f, mp4a.40.2",CLOSED-CAPTIONS=NONE
index_0_av.m3u8
...more renditions
#EXT-X-STREAM-INF:AUDIO="aac",BANDWIDTH=3697000,RESOLUTION=1280x720,CODECS="avc1.4d001f, mp4a.40.2",CLOSED-CAPTIONS=NONE
index_6_av.m3u8

The video plays fine in both the sender and receiver app, I can see both audio tracks in the sender app, but when casting to the receiver there are no controls for changing the audio tracks.

When accessing the AudioTracksManager's getTracks() method while intercepting the LOAD message like so...

playerManager.setMessageInterceptor(
  cast.framework.messages.MessageType.LOAD, loadRequestData => {
    loadRequestData.media.hlsSegmentFormat = cast.framework.messages.HlsSegmentFormat.TS
    const audioTracksManager = playerManager.getAudioTracksManager();
    console.log(audioTracksManager.getTracks())
    console.log('Load request: ', loadRequestData);
    return loadRequestData;
  });

I get an error saying:

Uncaught Error: Tracks info is not available.

Maybe unrelated, but super weird: I can console.log the request's media prop and see its tracks prop (an array with the expected 1 video and 2 audio tracks), however, if I try to access the tracks property in the LOAD message interceptor I get undefined.

I currently cannot look into the iOS sender code yet, so I tried to eliminate error sources on the receiver end. The thing is:

I always assumed that the receiver identifies alternative audio tracks on its own when loading HLS playlists. Is this assumption correct or can the AudioTracksManager only access tracks that have been previously defined in a sender app?

I couldn't find a clear statement on that in the Google Cast reference...

回答1:

Ok, feeling stupid for the time I spent on this, but I'm finally able to answer my own question. I didn't realize that I was accessing the AudioTracksManager in the wrong place - namely in the LOAD message interceptor instead of in a PLAYER_LOAD_COMPLETE event listener (as it is properly documented here)

After placing my logic into this event listener I was able to access and programmatically set my audio tracks.

So to answer my original question: Yes, the receiver app automatically identifies alternative audio tracks from an HLS playlist.

来源：https://stackoverflow.com/questions/54534043/does-v3-google-cast-receiver-parse-alternative-audio-tracks-from-an-hls-master-p

标签

google-cast

http-live-streaming