I have tried it on 72 MB video:
ffmpeg -y -hwaccel cuda -i /home/data1/protected/Media/Pictures/Pictures/Year-2025/03/2025-03-13/VID_20250313_154150.mp4 -vcodec libx264 -crf 28 -vf "pad=ceil(iw/2)*2:ceil(ih/2)*2" output.mp4
and I included -hwaccel cuda which sped up probably.
Result is 17M video and I see nothing strange as human. Looks same, it means compression is really good. Though it wasn't 94%, rather 77%.
Different ffmpeg formula
I have a bit different conversion formula, for videos on websites, I follow Google guideliness and compress it to webm:
(defun video2webm-dired ()
"Converts any video to webm"
(interactive)
(let* ((bitrate (read-number "Bitrate: " 500))
(videos (dired-get-marked-files))
(videos (mapcar 'video-mime-type-p videos))
(videos (seq-remove 'null videos))
(async-shell-command-buffer 'new-buffer)
(command (format "ffmpeg -y -hwaccel cuda -i `?` -c:v libvpx-vp9 -b:v %sk -pass 1 -passlogfile `?` -speed 4 -c:a libopus -f webm /dev/null -async 1 -vsync passthrough && ffmpeg -y -hwaccel cuda -i `?` -c:v libvpx-vp9 -b:v %sk -pass 2 -passlogfile `?` -speed 1 -c:a libopus \`?`.webm -async 1 -vsync passthrough && rm `?`-0.log;" bitrate bitrate)))
(dired-do-async-shell-command command nil videos)))
that however, takes much longer time than your formula. I have now converted to 1000 bit rate, and I have got result of 5.4 M for same video.
That is like 92.5%
I can't see as human any visible differences with that bit rate.
Better to 500 bit rate
With 500 bit rate, I have got 2.9M from 72M, that is fantastic. It took longer, but compression is so much better.
I have achieved basically 96% which is more than you! π
