ffmpeg - Conversions - Convert H264 to AV1 - libaom - Constrained Quality

libaom-av1 has a constrained quality (CQ) mode that will ensure that a constant (perceptual) quality is reached while keeping the bitrate below a specified upper bound or within a certain bound.

This method is useful for bulk encoding videos in a generally consistent fashion.

time ffmpeg -i a.mp4 -c:v libaom-av1 -crf 30 -b:v 2000k -f mp4 out.mp4

returns:

...
real	104m57.062s
user	599m4.884s
sys	0m32.345s

NOTE:

Input test size: 75.5M
Output test size: 4.8M

NOTE: The quality is determined by the -crf, and the bitrate limit by the -b:v where the bitrate MUST be non-zero.

crf: This value can be from 0–63.
- Lower values mean better quality and greater file size.
- 0 means lossless.
- A CRF value of 23 yields a quality level corresponding to CRF 19 for x264 (source), which would be considered visually lossless.