Video distortion with VA-API decoder when fast forwarding and rewinding [AMD / radeonsi_drv_video]

When VAAPI is enabled and H.264 videos are fast forwarded and rewound in Firefox, some distortions can appear for brief periods, but they go away as video continues playing.

Observed for example with this video:

https://mirrors.dotsrc.org/blender/blender-demo/movies/BBB/bbb_sunflower_1080p_60fps_normal.mp4

Try using left and right arrow keys a bunch of times for fast forwarding and rewinding.

• OS: Debian testing.
• GPU: Sapphire Pulse RX 6800 XT.
• Mesa: 22.3.3
• vainfo: Driver version: Mesa Gallium driver 22.3.3 for AMD Radeon RX 6800 XT (navi21, LLVM 15.0.6, DRM 3.49, 6.1.9)
• ffmpeg: 5.1.2.
• Firefox: 110.0b9

See corresponding bug on Mozilla bug tracker: https://bugzilla.mozilla.org/show_bug.cgi?id=1772028

The issue was isolated to AMD only, so it's likely a Mesa bug.