I'm not sure since when, but MP4 videos are not playable anymore on Firefox. There's an error message in the Web-Console saying HTTP-Content-Type "video/mp4" is not supported.
OS: OpenSuse Tumbleweed
Firefox version: 83.0 (64bit)
Installed packages (among others):
ffmpeg-4, gstreamer-plugins-libav, libavcodec56, libavcodec57, libavcodec58_91, libavdevice56, libavdevice57, libavdevice58_10, libavfilter5, libavfilter6, libavfilter7_85, libavformat56, libavformat57, libavformat58_45, libavutil54, libavutil55, libavutil56_51
about:config settings that might be important:
media.ffmpeg.enabled = true
media.mp4.enabled = true
media.mediasource.mp4.enabled = true
Still, I'm getting on the Konsole:
MediaSource.isTypeSupported("video/mp4") false
Anything else that might be necessary? Principally it works, because Firefox on my other box runs embedded MP4 videos just fine.
Diagnostics:
As suggested in the comment, I've downloaded the video and run ffprobe on it:
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'EprnqfLXYAgJV-e.mp4': Metadata: major_brand : mp42 minor_version : 0 compatible_brands: mp41isom Duration: 00:00:02.20, start: 0.000000, bitrate: 55 kb/s Stream #0:0(und): Video: h264 (avc1 / 0x31637661), none, 200x200, 51 kb/s, 10 fps, 10 tbr, 100 tbn, 100 tbc (default) Metadata: handler_name : Twitter v2 Unsupported codec with id 27 for input stream 0
The Accept header for the video is also a bit suspicious, no mp4 there (and I'm getting status 206):
Accept: video/webm,video/ogg,video/*;q=0.9,application/ogg;q=0.7,audio/*;q=0.6,*/*;q=0.5
ffprobe -hide_banner thevideo.mp4
.