ffmpeg is installed == From twitter web page: error in web console: For example, on twitter i get a "the media could not be played" placeholder and this in the web console: <i><b> HTTP “Content-Type” of “video/mp4” is not supported. Load of media resource https://video.twimg.com/amplify_video/1149302678771683333/vid/1280x720/qFCcMLAnjR_MBans.mp4?tag=13 failed. home 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" </i></b> When i click on that link in the error it saves the video to /tmp and plays it in ffplay.. and in preferences->Applications, video/mp4 shows up with ffplay configured. == Plays fine with a local file When I put that mp4 link in the address bar, it gives me a download dialog, I can download that file, and play it in firefox from the command line: firefox qFCcMLAnjR_MBans.mp4 == Plays fine with a local html file with the video control html element: When i open a local html file with the video control element that plays the video. So why do I get those errors when this is viewed on the twitter website? Any pointers appreciated. Thanks!