After recently upgrading to Ubuntu 18.10, Firefox isn't playing any embedded MPEG-4 video, there was no issue before the upgrade
The console in dev tools reports this
The video on this page can’t be played. Your system may not have the required video codecs for: video/mp4; codecs="avc1.42E01E mp4a.40.2", video/quicktime; codecs="avc1.42E01E mp4a.40.2", video/x-m4v; codecs="avc1.42E01E mp4a.40.2" 1 1066421472464392192 HTTP “Content-Type” of “video/mp4” is not supported. Load of media resource https://video.twimg.com/tweet_video/DskVIELXgAEDAmP.mp4 failed. 1 twitter
YouTube videos play successfully, and the same link works in Chrome on the same machine. Unfortunately, I'm using 56.0.2 and, due to work restrictions, cannot upgrade to the latest release
Flashplugin-installer and ffmpeg are installed and the latest version
The "Play DRM-controlled content" option is selected
Adding ffmpeg gstreamer and flashplugin-installer has no effect
sudo apt-get install ffmpeg flashplugin-installer gstreamer1.0 Reading package lists... Done Building dependency tree Reading state information... Done gstreamer1.0-plugins-good is already the newest version (1.14.4-1ubuntu1). gstreamer1.0-plugins-good set to manually installed. ffmpeg is already the newest version (7:4.0.2-2). flashplugin-installer is already the newest version (22.214.171.124ubuntu0.18.10.1). 0 upgraded, 0 newly installed, 0 to remove and 0 not upgraded.