Show subtitles on the Styled Media Receiver Google Cast with communication messages

Question

I am trying to start an mp4 stream on a Chromecast that also shows the subtitles (vtt files)

I saw that it was added in the native libraries. But I could not find the payload messages that are used to send this to the receiver app. I am not using the native libraries for android & iOS but the a Flutter version that uses the payload messages instead of the native libraries. -> https://github.com/jonathantribouharet/flutter_cast

This is what I already tried.

{
      'type': 'LOAD',
      'autoPlay': true,
      'currentTime': currentTime,
      'media': {
        'contentId': url,
        'contentType': 'video/mp4',
        'streamType': 'BUFFERED',
        'metadata': {
          'type': 0,
          'metadataType': 0,
          'title': title,
          'images': [
            {
              'url': posterUrl,
            }
          ],
        },
      },
      'customData': {
        'cc': {
          'tracks': [
            {'src': 'https://gist.githubusercontent.com/samdutton/ca37f3adaf4e23679957b8083e061177/raw/e19399fbccbc069a2af4266e5120ae6bad62699a/sample.vtt'},
          ],
          'active': 0
        },
      },
    }

And this is my full app: https://github.com/vanlooverenkoen/flutter_cast_ui/tree/feature/cast-ui

But the custom data is not doing anything.

All the StackOverflow issues I find are from 2014. Since then it should be possible with ClosedCaptions or subtitles via 3 file formats: WebVTT, TTML and CEA-608.

• https://developers.google.com/cast/docs/web_receiver/tracks#closed_captions_subtitles
• https://developers.google.com/cast/docs/media#subtitles_and_closed_captions

This documentation is used for the play/pause/stop implementation:

• https://developers.google.com/cast/docs/reference/messages
• https://docs.rs/crate/gcast/0.1.5/source/PROTOCOL.md

Stackoveflow issues I've already seen:

• Styled media receiver source (Chromecast)
• Google Cast - Subtitles with the Styled Media Receiver?
• Cast Receiver App does not show subtitles

Answer 1

I don't have experience with this, but you could check out this repo. It uses cpp to do a similar thing and provides a way to build a payload including text/vtt with a link for the subtitles. So you could expand the tracks object with more data

    msg["media"]["tracks"][0]["language"] = "en-US";
    msg["media"]["tracks"][0]["name"] = "English";
    msg["media"]["tracks"][0]["type"] = "TEXT";
    msg["media"]["tracks"][0]["subtype"] = "SUBTITLES";
    msg["media"]["tracks"][0]["trackId"] = 1;
    msg["media"]["tracks"][0]["trackContentId"] = yourSubtitleUrl;
    msg["media"]["tracks"][0]["trackContentType"] = "text/vtt";