I have the exact same problem, and a new that started just a few days ago. First, most embedded videos animated gifs play OK for me in Twitter; but increasing numbers of them do not. In all cases, the videos will play in Chrome (for which I am not logged in on Twitter). I can't find any settings in my twitter account that might affect this, so I think there is a FireFox setting that I need to fix.

The new problem is shown below. The video button is "X-ed" out, whereas in the other problem (as stated by the OP) and initial frame of the video is visible and the there is an actual start button.

The two problems may be related.

You can check the Web Console for media related messages.

• "3-bar" menu button or Tools -> Web Developer
• https://developer.mozilla.org/en-US/Tools/Web_Console

I'm sorry guys, I'm still having this problem. In my case, they do not work in Chrome either, and that's why I suspect that the problem might not be browser related. Anyways.

I also would like to add that Vimeo videos do not play either. The player shows up, with controllers, but when I click play, it loads the video (I can see the data coming through in the "network" tab of the developer tools) but does not start. The throbber (loading animation) shows but does not go away. [edit: Vimeo videos *do* play if I go through their site, if it's embedded then they behave as described above]

No solutions at all? If I need to provide information about my build I'll be glad to do it.

What does the Web Console show? If you lack support for playing media files on your computer then this could be a possible cause. If it doesn't work in other browsers as well then you may have a problem with security software. Google Chrome usually comes with its own builtin support and doesn't rely on native OS support like Firefox.

cor-el said

What does the Web Console show?

Nothing relevant. No errors at all, related to the video. I even set the level of the console to debug, couldn't find any message there.

If you lack support for playing media files on your computer then this could be a possible cause. If it doesn't work in other browsers as well then you may have a problem with security software. Google Chrome usually comes with its own builtin support and doesn't rely on native OS support like Firefox.

No, it's the browser. If I download the video and use an external player (I use VLC) the video DOES play. The problem is with the browser itself. Chrome does not play either.

Vimeo videos load the placeholder image and all controls, normally. When I click play, it loads the first segments of the videos (I can see this in the console) but does not play. It shows the throbber and stays there.

Does the Network Monitor show a request to download the video?

• https://developer.mozilla.org/en-US/Tools/Network_Monitor

cor-el said

Does the Network Monitor show a request to download the video?

Yes. When I click play, it makes three requests to the server. Vimeo loads "segments" of the video, it seems that they're the first segments.

I've attached an example image. It stucks in this "loading" state eternally.

[edit] Just tested in Opera. Fresh new installation, downloaded, installed, first page opened was the one from screenshot attached. Same behavior: it loads, but does not start playing. As of right now I am almost convinced that it's a problem outside Firefox.

I'm bumping this, because it's annoying. Twitter videos work, but animated GIFs (which are also videos in disguise in Twitter) do not.

Also, some Vimeo videos do not work.

YouTube works perfectly.

It's not Firefox exclusive. Just installed Vivaldi, same problem (GIFs freeze on the first frame).

Is there a way to debug video codecs on browser? Or reinstall them? I'm leaning towards this, because it's not browser specific. But the weird thing is that, if I download the video and play it with VLC locally, it works.

Please, guys. Anyone?

Can you confirm that this only happens with GIFV files (likely MP4 media) if you check this in the Inspector ? Are there media related messages in the Web Console?

• https://developer.mozilla.org/en-US/Tools/Page_Inspector/How_to/Examine_and_edit_HTML
• https://developer.mozilla.org/en-US/Tools/Web_Console

I'm not sure what you mean by "check in the Inspector". If you mean the web developer console, then inspecting the HTML video element, yes, it's a mp4 file.

I'm not seeing any media related messages in the Console.

This video works: https://twitter.com/FIFAWWC/status/1176276306427707394

This one does NOT: https://twitter.com/JimMFelton/status/1176171959916408833

I reported the same problem back in July (above). No improvement since then. I am at a total loss on how to use Inspector and the other developer tools.

Several of us here need more detailed help. Can this issue be elevated somehow?

I just made of movie of what Inspector shows when I click one of these GIFs, but only images can be uploaded on this site. How can I get the movie to a tech helper?

Can you play the video directly?

• https://video.twimg.com/tweet_video/EFKRTAFW4AAQHrC.mp4
• Codec: H264 - MPEG-4 AVC (part 10) (avc1)

No. This is what I get (screenshot attached). Nothing happens if I click on the play button.

I tested this same URL in Chrome, Opera and Vivaldi. None of them play the video.

But if I download it as a file on my computer, then VLC does play it.

I can view that one in my browser. It's an mp4, and what I'm having trouble with is *some* video-gifs (which play OK in Chrome).

Where can I send the movie I made (see three posts above) of what Inspector shows when I activate for one of those GIFs?

This happens to me, but only on Android and Windows 7

My issue may be similar. (I made another post https://support.mozilla.org/en-US/questions/1270502 ) I cannot play the video posted by cor-el in Firefox either, but I can play it in Opera.

At last -- after months I have isolated the problem in my Firefox setup, BUT I have yet to find a satisfactory solution. I found the problem by starting Firefox in safe mode; a problem twitter tweet then had its embedded video working perfectly.

The problem is extensions I have tried so that Twitter shows its old user interface (instead of the new, very clumsy one that frustrates many users). These extensions seem to work well, except for this problem. They are: Old Twitter Layout, and Twitter Old UI.

I had thought I was running up against a Firefox codec limitation, because when inspecting offending tweets with Web Developer | Web Console this fault was displayed: <Quote> Cannot play media. No decoders for requested formats: 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", application/x-mpegURL, video/mp4; codecs="avc1.42E01E mp4a.40.2" <End Quote>

Are you others here who have been having this problem also trying to run Twitter with its classic interface?

Can one of the Mozilla tech volunteers here try to elevate this so that perhaps a solution can be found through a patch to Firefox? I have already posted reviews with the specifics to the authors of the above two FF extensions.

No. Twitter GIFs do not display in either interface. They also don't work in safe mode. I have no extensions in my Firefox installation. And my case really does not seem to be Firefox related as I was suspecting, because all browsers have the same problem. I have no messages in Web Console. There must be some problem with my machine here, maybe a misconfiguration of video libraries.

What baffles me is that the downloaded video played by an external player (like VLC) works. But inside the browser it does not.

I'm sorry for opening this, I'm seeing no solution. I should reinstall my OS, it's an old system. Hope that other that have similar problems here manage to solve theirs.

Thanks for the efforts, guys.

I'm now using Linux Mint and have duplicated the same "GIFs don't play problem" there as well, so it's NOT strictly a Windows 7 issue. In this case, the first frame will display and nothing else.