I’m working on an SPA where one can watch VODs in sync, as if it was live.

I noticed something weird on several videos: when started at a late position on Auto quality, the videos plays normally for a few seconds, then goes backward exactly when the quality is automatically changed.
This does not happen by switching qualities manually.

This is not easy to reproduce, as you need to be in Auto quality AND have the first selected quality to be low (e.g. 360p).

Here are the steps I took with relative success to reproduce the issue:

1. Go to this video : https://www.twitch.tv/videos/999197520?t=8h51m36s
2. Switch to a low quality (360p)
3. Let the video run for a few seconds
4. Switch to auto quality and refresh
5. If you’re lucky, you should be in Auto quality with 360p selected. If you have “Source” quality, go back to step 2
6. Around 8:51:51, the video should have jumped backward of a few minutes (but the timecode hasn’t). This happen exactly at the moment where the video switches quality.

I made a video showing the steps to reproduce and the bug here : https://youtu.be/s4TGLqzBg6k

My guess is that it is due to the long video and a somewhat wrong video encoding from the streamer…
I found a work-around by forcing a non-Auto quality in my SPA, but this removes the advantages of the Auto quality mode…

Foot Note : this also happens with the embed Twitch player.