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Major blocking issue on preset 12(13)

Repro steps

  1. Get SVT-AV1 2.1.0
  2. Download balenciaga.mp4
  3. Encode video with following settings:

ffmpeg -hide_banner -loglevel error -i balenciaga.mp4 -pix_fmt yuv420p10le -map 0:v:0 -c:v libsvtav1 -svtav1-params preset=12:keyint=300:crf=50 -an balenciaga.ivf

Observations

Encoded visual quality is incredibly bad, and resulting video is unusable. There are frames with brief flashes of light that get encoded with random dark blocks. For example, this is frame 87:

Preset 12(13) Preset <= 11
p12.png p11.png

This blocking issue is actually more noticeable than even #2189, as the bright blocks inconsistently fade in and out throughout the entire mini-gop (tens of frames), when in reality the "flash" occurs in one single frame.