>>106119598
>>106115937
Yeah, I really don't know what's wrong.
I tried to make a new video passing less parameters and it still gives me picrel.
ffmpeg -loop 1 -i in.jpg -i in.mp3 -c:v libx264 -pix_fmt yuv420p -vf "pad=ceil(iw/2)*2:ceil(ih/2)*2" -c:a aac -shortest -y out.mp4
The padding is because the picture has to have a width and a height both divisible by 2.

The video works just fine on firefox itself and on mpv to, I'm confident it's a 100% valid video file, so at this point I don't know what to do desu.
I hate to be stuck with webm.

Maybe it's my build of ffmpeg that doesn't work?
Or maybe it adds some sort of weird defaults that fuck up the .mp4 in a way 4chan doesn't like?
I got it from https://www.gyan.dev/ffmpeg/builds/packages/ffmpeg-2025-07-31-git-119d127d05-essentials_build.7z linked on https://ffmpeg.org/download.html#build-windows