I'm going to ask you guys for help.
The problem is in this file.
https://github.com/vichan-devel/vichan/blob/master/inc/lib/webm/ffmpeg.phpThe error "invalidwebm" is triggered on line 39, this is because for some reason, with certain webms the video's width and height (resolution) can't be defined. I imagine neither the duration or anything else isn't properly parsed for some reason.
https://github.com/mpv-player/mpv/issues/5118I believe this is the same bug, as I cannot even transcode these certain webms with ffmpeg locally, while copying the video stream. I get the error "Invalid return value 0 for stream protocol" when running something like this:
ffmpeg -i in.webm -c copy out.webm
This is the same issue. I believe this is the problem, I will look into it.