Bug 275665 – iPadOS: Playback of AVC3 video with MSE happens at the wrong rate; starts and stops.

• Component: Media
• Status: NEW

[Robert Bryer]

Created attachment 471707 [details]
Video is playing back very quickly and stopping/starting; audio is playing back correctly

On iPadOS only; Safari desktop is unaffected:

Some live streams we make are playing back the video track really quickly. We see about 5-10 seconds of video get played within a second; and then it stops while the audio(playing at the correct rate) catches up. The attached video shows this.

And you can reproduce here with an iPad:
https://is.gd/hdHwIV

I'm mentioning AVC3 because I think that's slightly novel(I understand most people use AVC1) and AVC3 moves the location of the SPS and PPS units (containing frame rate information). Perhaps these units aren't being found?

We do however have some other content in AVC3 that plays fine; the difference there is that it's not a live stream and the timestamps aren't unix epochs.

Strangely, removing the audio track makes it play back completely fine:
https://is.gd/o6357E

So perhaps there is some contamination between the tracks?

iPadOS 16.7.8 but definitely earlier versions too.

[Alexey Proskuryakov]

Thank you for the report! Would you have the opportunity to also test iPadOS 17 and/or 18 beta?

I don't have an iPad handy right now, but on an iPhone with iOS 18, this video doesn't start playing at all.

[Robert Bryer]

So the example is using Media Source Extensions, so it won't work on iPhone.

And my iPad is a Gen5 and is capped at iPadOS 16, so I can't update to the beta versions either.

[Robert Bryer]

I wanted to know why only our simulcast streams were failing but not VOD output, so after a while I found that rebasing the timestamps to 0 also fixes it:

https://is.gd/GhJVpd

This example works and it's using the sourceBuffer.timestampOffset property so that the buffered range here starts from 0, instead of starting at an epoch-time(1718792755.2 in the failing example).

I can start the buffer range at numbers as high as 100000 without a problem, but more seems to cause it to stutter; so this is possibly something caused by big timestamps?

[Alexey Proskuryakov]

For what it's worth, I can reproduce on iPadOS 17.5.1. Other than that, will need for CC'ed experts to weigh in.

[Radar WebKit Bug Importer]

<rdar://problem/130588154>