Disabling inflight subtitle playlist prevents segments from ever loading

[andreasschrottenbaum]

What version of Hls.js are you using?

1.5.x

What browser (including version) are you using?

Chrome

What OS (including version) are you using?

macOS

Test stream

https://codepen.io/3qgmbh/pen/MWdgKVK

Configuration

{
  autoStartLoad: false
}

Additional player setup steps

No response

Checklist

• The issue observed is not already reported by searching on Github under https://github.com/video-dev/hls.js/issues
• The issue occurs in the stable client (latest release) on https://hlsjs.video-dev.org/demo and not just on my page
• The issue occurs in the latest client (main branch) on https://hlsjs-dev.video-dev.org/demo and not just on my page
• The stream has correct Access-Control-Allow-Origin headers (CORS)
• There are no network errors such as 404s in the browser console when trying to play the stream

Steps to reproduce

When I try to Change to the first textTrack, there is no reaction.

The other tracks can be changed as expected, but choosing the first one doesn't have an effect.

The code works up until HLS 1.4.14, but on 1.5.x it's broken.

Example Codepen: https://codepen.io/3qgmbh/pen/MWdgKVK

Expected behaviour

You can choose the first texttrack

What actually happened?

When choosing the first texttrack, the last message (if existing) keeps being displayed

Console output

[log] > [subtitle-track-controller]: Switching to subtitle-track 0 "English" lang:en group:textstream

contrary to the other texttracks, there is no more output after this line. Video was buffered and paused

Chrome media internals output

No response

[robwalch]

I'm unable to reproduce the issue on the demo page with "autoStartLoad": false in the config and executing hls.startLoad() to begin streaming.

https://hlsjs-dev.video-dev.org/demo/?src=https%3A%2F%2Fsdn-global-streaming-cache.3qsdn.com%2Fstream%2F27816%2Ffiles%2F24%2F01%2F11%2F9207963%2F27816-v6CQ3mJwkTHNBGb.ism%2Fmanifest.m3u8&demoConfig=eyJlbmFibGVTdHJlYW1pbmciOnRydWUsImF1dG9SZWNvdmVyRXJyb3IiOnRydWUsInN0b3BPblN0YWxsIjpmYWxzZSwiZHVtcGZNUDQiOmZhbHNlLCJsZXZlbENhcHBpbmciOi0xLCJsaW1pdE1ldHJpY3MiOi0xfQ==

In your reproduction example, the english subtitle playlist is requested on start. It is the default track and will be loaded when you begin loading on manifest_parsed. The issue is related to disabling the subtitle track while it is being loaded. This results in the level details never being stored in subtitle-stream-controller because of an early return (Subtitle track 0 loaded is never logged, and the track-controller maintains that it is loaded and will not reload it):

hls.js/src/controller/subtitle-stream-controller.ts

Lines 267 to 279 in 2c19c5c

	private onSubtitleTrackLoaded(
	event: Events.SUBTITLE_TRACK_LOADED,
	data: TrackLoadedData,
	) {
	const { currentTrackId, levels } = this;
	const { details: newDetails, id: trackId } = data;
	if (!levels) {
	this.warn(`Subtitle tracks were reset while loading level ${trackId}`);
	return;
	}
	const track: Level = levels[currentTrackId];
	if (trackId >= levels.length || trackId !== currentTrackId || !track) {
	return;

You could either remove the default tag from the subs or not disable subtitles on start to workaround this issue for now.

[andreasschrottenbaum]

Thank you for that fast response!

What I figured out inbetween: When I set the track to null instead of -1, it works

[robwalch]

What I figured out inbetween: When I set the track to null instead of -1, it works

That's clever. I guess this produces the warning Invalid subtitle track id: null? Try setting hls.subtitleTrack to -1 (rather than null) right after calling loadSource. Doing this before the manifest is parsed prevents default selection and loading of subtitle playlists:

hls.js/src/controller/subtitle-track-controller.ts

Lines 377 to 379 in 2c19c5c

	set subtitleTrack(newId: number) {
	this.selectDefaultTrack = false;
	this.setSubtitleTrack(newId);