Recommended settings for low-resolution encoding with --hevc-aq
...This was originally posted on the mailing list
I use libx265 via the ffmpeg plugin. I find that enabling --hevc-aq (with -x265-params "hevc-aq=1"), reduces bit-rate by a very large amount (keeping crf constant). The output quality is excellent for 480p and higher resolutions. However, for 360p/240p etc, enabling --hevc-aq tends to produce some pixellation. This is particularly prominent around the edges of objects in the video.
I understand that there is no free lunch, and the reduction in bitrate (at same crf) between --no-hevc-aq and --hevc-aq does mean that there will be some quality loss. But are there some parameters that can be tuned to minimize this blocking/pixellation ?
For example, in my tests, using 10-bit output (-pix_fmt yuv420p10le) and changing to a slower preset ('slow' or 'slower' instead of medium) seems to help. Are there any other parameters that could be modified?
thanks.