libx265 passlog/mbtree file reuse for lower resolutions 2-pass encoding. $350 USD bounty.

[Mista_D]

Looking for a method to run HEVC pass1 once at 4K resolution. And then re-use same one passlog file to encode ABR set - 4K, 1080p, 720p, 480p and 360p files all at various bitrates please.

This has been done before in June 2012 by "the one and only" Dark Shikari, his patch is attached for reference.

expected behaviour:

ffmpeg -y -i 4k_foo.mp4 \
-x265-params pass=1:stats=bar -c:v libx265 -f mp4 /dev/null

ffmpeg -y -i 4k_foo.mp4 \
-x265-params pass=2:stats=bar -c:v libx265 4k.mp4 \
-x265-params pass=2:stats=bar -c:v libx265 -s 1280x720 720p.mp4

[Mista_D]

x264 mbtree rescale diff

[Mista_D]

Producing same video compression results as with uniqely produced passlog file, with at most 2-3% percent bitrate penalty.

libx264 takes 2% quality hit, when using passlog/mbtree from 1080p pass 1 to encode 720p file.