What parameters to use to convert videos to av1 with SVT-AV1 with FFmpeg

[ignace72]

Hello to all.
The AV1 format is known to have a compression ratio of 30 to 40% better than H265 at equal quality yet after many tests with FFmpeg and svt-av1 for a 720p video with 5.1 audio of 1 hour 53 I end up with either a 350 MB video of mediocre quality with the default settings or 4 GB of good quality while the h265 video of good quality is 1 GB.
For the video in AV1+Opus of good quality, but of enormous size, I use the following command:

ffmpeg -i video.720p.5.1.x265.mkv -vcodec libsvtav1 -y -rc 1 -preset 5 -acodec libopus -af channelmap=channel_layout=5.1 -b:a 250k -vbr on video.720p.5.1.av1.opus.mkv

I have tried several settings, but each time.it always gives me either poor quality files of small size or too big files of good quality.
Do you know any settings to get a compression ratio in AV1 of 30-40% better than H265 of equal quality with the SVT-AV1 encoder?
Thank you.
Ignace.

[ignace72]

Referring to a refer to a ticket from FFmpeg https://trac.ffmpeg.org/ticket/9610 which gives a two-pass usage with the following commands, because FFmpeg does not offer all the options included in SvtAv1 :

ffmpeg -i Infile.mp4 -map 0:v:0 -pix_fmt yuv420p10le -f yuv4mpegpipe -strict -1 - | SvtAv1EncApp -i stdin --preset 6 --keyint 240 --input-depth 10 --crf 30 --rc 0 --passes 1 --film-grain 0 -b Outfile.ivf
ffmpeg -i Outfile.ivf -i Infile.mp4 -map 0:v -map 1:a:0 -c:v copy -c:a copy FinalProduct.mp4

I'm going to test this and I'll come back here to give the results I get with these two commands.
Ignace.

[ignace72]

Well, that's it, it finished converting, it's slow (8,4 fps) but it works, the quality of the video is obviously identical to the original.
The starting file in H265 AC-3 5.1 is 1 Gio and the file in av1 opus 5.1 is 769 Mio what gives me 33,16 % of gain of size what is not negligible therefore the test is rather positive.
For the second command, I did this one (600 fps):

ffmpeg -i Outfile.ivf -i Infile.mp4 -map 0:v -map 1:a:0 -c:v copy -c:a libopus -af channelmap=channel_layout=5.1 -b:a 250k -vbr on FinalProduct.mkv

for a stereo video, I would have done this one:

ffmpeg -i Outfile.ivf -i Infile.mp4 -map 0:v -map 1:a:0 -c:v copy -c:a libopus -b:a 128k -vbr on FinalProduct.mkv

The process took 5 hours 55 minutes.
Ignace.

[ignace72]

Hello to all.
I did another test on a file in H265 Opus 5.1 which is 1.2 Gio and the file in Av1 Opus 5.1 is 853.5 Mio which gives 43.97% gain in size, it's even better than the first video, it was even slower (6.6 fps) and the quality of the video is still visibly identical to the original.
The process took 6 hours 41 minutes.
Now, I will test on small H265 Opus files in stereo from 350 to 600 Mio to see if the gains are in the same range.
Ignace.

[ignace72]

Well, I made two other tests.
A video of 1h55 with a resolution of 720x512px (DVD quality), H265 Opus stereo of 531,9 Mio in Av1 Opus stereo of 430,7 Mio which gives 19,03 % of gain of size with a speed of 13 fps of a duration of 3h56.
A video of 1h56 of resolution of 512x280px, H265 Opus stereo of 346,9 Mio in Av1 Opus stereo of 365,9 Mio what gives 5,48 % of deficit of size with a speed of 19 fps and a duration of 2h38.
That's it.
Am I to understand that I have reached the limits of the SvtAv1 encoder or is there a possibility to optimize the compression for low resolution files?
That's the question.
Ignace.