Parse CHANNELS Attribute in EXT-X-MEDIA

[kickermeister]

Is your feature request related to a problem? Please describe.
I need to know the channel number of streams for certain applications. See e.g. https://storage.googleapis.com/shaka-demo-assets/angel-one-hls/hls.m3u8

Describe the solution you'd like
Parse the CHANNEL attribute in EXT-X-MEDIA and provide the information in the audioTracks object for every audioTrack.

Describe alternatives you've considered
As there is no simple way to detect the channel number from a HTML5 media element, I would need to write or use a separate HLS parser.

[itsjamie]

It would be good to provide this information, however, like you mentioned the audioTracks API doesn't have a standard property to include the channel count.

I would definitely think that it would be a good idea however to include the ability to be able to connect an audio track to its source track in the HLS manifest and retrieve this metadata.

Perhaps an API that takes the id property of the audio track and retrieves this?

[kickermeister]

Perhaps an API that takes the id property of the audio track and retrieves this?

I don't have strong feelings about the implementation, the existence of the functionality is more important to me. It would be handy, however, if the audioTracks API could be extended with the channel count information (if that's easily possible).

[kickermeister]

I just realized that RFC 8216 is pretty strict regarding the CHANNELS attribute (see https://tools.ietf.org/html/rfc8216#section-4.3.4.1):

  All audio EXT-X-MEDIA tags SHOULD have a CHANNELS attribute.  If a
  Master Playlist contains two Renditions encoded with the same
  codec but a different number of channels, then the CHANNELS
  attribute is REQUIRED; otherwise, it is OPTIONAL.

The CHANNELS attribute would be, however, also very useful for other use cases where more than two audio channels are used.

[robwalch]

@kickermeister The ticket title and description read CHANNEL, but you're referring to the CHANNELS attribute correct?

I think we should include EXT-X-MEDIA attributes (attrs) on track objects the same we include EXT-X-STREAM-INF attributes on level objects:

hlsManifestParsed ({
    "levels": [
        {
            "attrs": {
                "BANDWIDTH": "827972",
                "AVERAGE-BANDWIDTH": "482170",
                "CODECS": "avc1.42c01e,mp4a.40.2",
                "RESOLUTION": "192x144",
                "AUDIO": "default-audio-group",
                "SUBTITLES": "default-text-group"
            },

No reason we don't other than it hasn't been implemented.

    "audioTracks": [
        {
            "groupId": "default-audio-group",
            "name": "stream_5",
            "type": "AUDIO",
            "default": true,
            "autoselect": true,
            "forced": false,
            "url": "https://storage.googleapis.com/shaka-demo-assets/angel-one-hls/playlist_a-eng-0128k-aac-2c.mp4.m3u8",
            "lang": "en",
            "audioCodec": "mp4a.40.2",
            "id": 0,

😢

[robwalch]

This feature is already implemented in feature/v1.0.0

@kickermeister Have you tried the v1 branch?

       {
            "attrs": {
                "TYPE": "AUDIO",
                "URI": "playlist_a-deu-0128k-aac-2c.mp4.m3u8",
                "GROUP-ID": "default-audio-group",
                "LANGUAGE": "de",
                "NAME": "stream_4",
                "AUTOSELECT": "YES",
                "CHANNELS": "2"
            },
            "bitrate": 0,
            "id": 1,
            "groupId": "default-audio-group",
            "name": "stream_4",
            "type": "AUDIO",
            "default": false,
            "autoselect": true,
            "forced": false,
            "lang": "de",
            "url": "https://storage.googleapis.com/shaka-demo-assets/angel-one-hls/playlist_a-deu-0128k-aac-2c.mp4.m3u8",
            "audioCodec": "mp4a.40.2"
        },

[kickermeister]

@robwalch Thanks for your reply, I was of course referring to the CHANNELS attribute (changed accordingly the title of this issue). The implementation in v1.0.0 branch seems to work properly. You may have good reasons but I'm still wondering whether the channels information which is in attrs object could be also added to the audioTrack object, like:

{
            "attrs": {
                "TYPE": "AUDIO",
                "URI": "playlist_a-deu-0128k-aac-2c.mp4.m3u8",
                "GROUP-ID": "default-audio-group",
                "LANGUAGE": "de",
                "NAME": "stream_4",
                "AUTOSELECT": "YES",
                "CHANNELS": "2"
            },
            "bitrate": 0,
            "id": 1,
            "groupId": "default-audio-group",
            "name": "stream_4",
            "type": "AUDIO",
            "default": false,
            "autoselect": true,
            "forced": false,
            "lang": "de",
            "channels": 2,
            "url": "https://storage.googleapis.com/shaka-demo-assets/angel-one-hls/playlist_a-deu-0128k-aac-2c.mp4.m3u8",
            "audioCodec": "mp4a.40.2"
        },

[robwalch]

You may have good reasons but I'm still wondering whether the channels information which is in attrs object could be also added to the audioTrack object

@kickermeister Because it's an optional attribute, and hls.js does not use channels internally, we haven't added it on the audioTrack objects. If we did, that could create the expectation for us to populate channels even when not present in the manifest (based on audio data like adtsChanelConfig for example). So best reason I can give is that I'm hoping to avoid that.

[robwalch]

I'm closing this one based on the comments above. If you have trouble working off feature/v1.0.0 let me know. Thanks!