Safari & Firefox skip video frames (are b-frames ignored?)

[Wumpf]

B-frames being ignored is the likely cause, but we should dig a bit deeper here to figure this out - would be great if we could show in the ui whether a frame is a bframe. On native h.264 we now show composition & decode timestamps which gets us almost there.

The issue can be reproed by loading this video into Rerun

bunny_timestamped_h264_1080p_10s.mp4

and then frame stepping.
I observed this on Mac Firefox, Safari but not in our native ffmpeg based impl or Chrome.

This is very likely the issue this users hit
https://x.com/chrisoffner3d/status/1847623631678943416