AV1 to VP9 doesn't support seeking (HLS)

[vidbin]

When converting a VP9 4k file to 1440p AV1 with av1_qsv and then converting again to 720p/480p VP9 with vp9_qsv seeking no longer works on the video. If I replace vp9_qsv with h264_qsv it works fine.

Well, to be more specific seeking does work but it takes a minute or two to start working.

This also occurs when the video is downloaded locally and playing directly in firefox.

Unsure if this is due to ffmpeg or the intel media driver. I'm using Linux with up to date packages.

Using ffmpeg git N-110065-g30cea1d39b.

How to reproduce:

ffmpeg -n 15 /usr/bin/ffmpeg -i /var/www/peertube/storage/streaming-playlists/hls/private/long-uuid-here/long-uuid-here-1440-fragmented.mp4 -y -acodec libopus -vcodec vp9_qsv -threads 24 -f mp4 -movflags faststart -max_muxing_queue_size 1024 -map_metadata -1 -pix_fmt yuv420p -b:a 128k -strict -2 -vbr on -vf scale=w=-2:h=480 -b:v 1250k -minrate 10k -maxrate 2000k -g 300 -hls_time 4 -hls_list_size 0 -hls_playlist_type vod -hls_segment_filename /var/www/peertube/storage/tmp/hls/long-uuid-here-480-fragmented.mp4 -hls_segment_type fmp4 -f hls -hls_flags single_file /var/www/peertube/storage/tmp/hls/long-uuid-here-480.m3u8"

Some peertube recorded errors:

warn[3/24/2023, 6:37:19 AM] Invalid end watch section 82. Last start record was at 170.

warn[3/24/2023, 6:37:24 AM] Invalid end watch section 87. Last start record was at 170.

warn[3/24/2023, 6:37:29 AM] Invalid end watch section 90. Last start record was at 170.

warn[3/24/2023, 6:45:09 AM] Invalid end watch section 0. Last start record was at 81.

[pearsche]

I still have to test more to report properly, but I think vp9_qsv is broken. On my own Intel laptop I can encode h264,hvec with qsv on linux properly but vp9_qsv does produce video, but when seeking, stops displaying anything but the last frame and only audio plays.

edit: uh, no, i can't, i just got hevc output just as broken...
edit2: h264_qsv produces video that is seekable properly, h265_qsv and vp9_qsv produce video that freezes when seeking using the arrow keys on players like totem (gnome videos) and mpv (with or without config file), h265_qsv video can recover if you seek to any point using the mouse cursor but seeking takes a second more than h264, and vp9_qsv video completely freezes after seeking in any way. In all 3 cases audio continues properly, and mpv outputs "[mkv] Discarding potentially broken or useless index."