HLS.js 1.5.1 doesn't start auto playing some HLS playlists until the user seeks manually

[bes]

What version of Hls.js are you using?

v1.5.1

What browser (including version) are you using?

Version 120.0.6099.234 (Official Build) (arm64)

What OS (including version) are you using?

macOS 14.2.1 (23C71)

Test stream

No response

Configuration

{
  "debug":false,
  "startPosition":-1,
  "maxBufferLength":30,
  "maxBufferSize":60,
  "startLevel":-1,
  "defaultAudioCodec":"mp4a.40.2",
  "abrEwmaDefaultEstimate":10000000
}

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

As usual I have a complex setup where I create an "off-screen" video element and pipe frames to WebGL, so I can't write the exact steps, but I would be happy to discuss my setup on Slack, as we have done before.

But in a nutshell, the video should start auto playing without user interaction, and it works on some playlists, but not others.

Worked great on 1.4.8.

(Sorry - I had to lie about the precondition checkboxes, since I can't reproduce this on the demo page)

Expected behaviour

The video to start playing without the user seeking manually

What actually happened?

HLS.js seems to stall, printing something like this, in a loop:

Live playlist, switching playlist, load frag with next SN: 513

Console output

hls.mjs:9897 [log] > [audio-stream-controller]: Live playlist, switching playlist, load frag with next SN: 513
19:44:49.076 hls.mjs:9897 [log] > [audio-stream-controller]: Live playlist, switching playlist, load frag with next SN: 513
19:44:49.177 hls.mjs:9897 [log] > [audio-stream-controller]: Live playlist, switching playlist, load frag with next SN: 513
19:44:49.276 hls.mjs:9897 [log] > [audio-stream-controller]: Live playlist, switching playlist, load frag with next SN: 513
19:44:49.377 hls.mjs:9897 [log] > [audio-stream-controller]: Live playlist, switching playlist, load frag with next SN: 513
19:44:49.476 hls.mjs:9897 [log] > [audio-stream-controller]: Live playlist, switching playlist, load frag with next SN: 513
19:44:49.576 hls.mjs:9897 [log] > [audio-stream-controller]: Live playlist, switching playlist, load frag with next SN: 513
19:44:49.676 hls.mjs:9897 [log] > [audio-stream-controller]: Live playlist, switching playlist, load frag with next SN: 513
19:44:49.777 hls.mjs:9897 [log] > [audio-stream-controller]: Live playlist, switching playlist, load frag with next SN: 513
19:44:49.876 hls.mjs:9897 [log] > [audio-stream-controller]: Live playlist, switching playlist, load frag with next SN: 513
19:44:49.977 hls.mjs:9897 [log] > [audio-stream-controller]: Live playlist, switching playlist, load frag with next SN: 513
19:44:50.077 hls.mjs:9897 [log] > [audio-stream-controller]: Live playlist, switching playlist, load frag with next SN: 513
19:44:50.176 hls.mjs:9897 [log] > [audio-stream-controller]: Live playlist, switching playlist, load frag with next SN: 513
19:44:50.277 hls.mjs:9897 [log] > [audio-stream-controller]: Live playlist, switching playlist, load frag with next SN: 513
19:44:50.376 hls.mjs:9897 [log] > [audio-stream-controller]: Live playlist, switching playlist, load frag with next SN: 513
19:44:50.476 hls.mjs:9897 [log] > [audio-stream-controller]: Live playlist, switching playlist, load frag with next SN: 513
19:44:50.576 hls.mjs:9897 [log] > [audio-stream-controller]: Live playlist, switching playlist, load frag with next SN: 513
19:44:50.677 hls.mjs:9897 [log] > [audio-stream-controller]: Live playlist, switching playlist, load frag with next SN: 513
19:44:50.776 hls.mjs:9897 [log] > [audio-stream-controller]: Live playlist, switching playlist, load frag with next SN: 513
19:44:50.877 hls.mjs:9897

Chrome media internals output

No response

[robwalch]

Hi @bes,

Can you provide a page that reproduces the issue please? Sharing an example in Slack would be fine.

[robwalch]

hls.mjs:9897 [log] > [audio-stream-controller]: Live playlist, switching playlist, load frag with next SN: 513
hls.mjs:9897 [log] > [audio-stream-controller]: Live playlist, switching playlist, load frag with next SN: 513

This sounds like you have a live playlist with unmuxed audio and video. There is no Program Date Time to align media on so it is going on whatever it loaded last (need complete logs to confirm). If playback is not starting that is likely because the loaded audio and video are not overlap (need complete logs to confirm but may not be possible without looking at the media and). When they don't overlap, there is no combined buffer that can be played - at least not at the initial live seek position for the first pair of segment. That is OK and expected if you have audio and video playlists with nothing to align on until media is parsed, but we then need parsed the media, append, realign and hope from there that the streaming controllers will fill in the gaps. So PDT is missing and the playlists are only aligned after media timestamps are parsed, but what if the playlists dont overlap now or we're in buffered video territory but audio is off by 1? That's my best guess for what is happening here.

I can't move forward though without a sample that reproduces the issue. A pointer to the offending commit would help too. I don't see a reason why this would require a complex setup to reproduce. It should be reproducible without WebGL copying, we just need the live stream, and maybe information on any deferral you might be performing between loadSource and attachMedia or startLoad as that could also impact where and when segments start being requested and appended for live.

[bes]

Sorry, I've been a bit swamped. I will try to make a repro for you as soon as I have a little bit of bandwidth.

[bes]

I have shared an HLS link with you privately @robwalch

[robwalch]

The video playlist is VOD (has #EXT-X-ENDLIST) but the audio track playlist is Live (no #EXT-X-ENDLIST). The player (latest and earlier versions) load an audio segment near the end on start. Older releases correct themselves, but latest does not (until a seek).