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Worked before but now-"Video format or MIME type not supported". Why?

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On a Mac with FF 31.0 I'm trying to view daily videos that I've watched for years and all of a sudden i get these messages. Could it have something to do with the new FF version I installed?

All Replies (9)

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You get this error when the HTML5 media player is used and not a Flash player.

Unfortunately there is no support for videos in the H.264 format videos on Mac, so if videos are offered in that format or in another unsupported format then you will get this error.

See also "What's the plan for H.264 on the Mac?":

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Thanks Cor-el. But I've watched these daily for years and it's only in the last few days that I get this error msg. I think it's unlikely that they would have changed the format on their end.

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Try to clear the cache and remove cookies only from websites that cause problems.

"Clear the Cache":

  • Firefox > Preferences > Advanced > Network > Cached Web Content: "Clear Now"

"Remove Cookies" from sites causing problems:

  • Firefox > Preferences > Privacy > "Use custom settings for history" > Cookies: "Show Cookies"

You can use the built-in Inspector to see what code is used for the player and what media files are available. There are probably also error messages in the Web Console or the Browser Console (Firefox/Tools > Web Developer).

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Thanks again Cor-el. I cleared the cache and removed several cookies but still get same error msg. FWIW, I usually listen to a weekly radio program (audio only) on the same site, and although I got no error msg, it would not play either. I tried the inspector and console tools but I couldn't understand them.

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Can you post a link to a publicly accessible page (i.e. no authentication or signing on required) with such not working media content?

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How do I change the slide show on my site,, so that it will be played successfully on any version of Firefox without the "no video with supported format and Mime type found" error message showing up? It shows up perfectly fine in IE.

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Hi OldWorldLace

You can using a simple video element to play this video with no fallback if the browser doesn't support this MP4 video via the video tag.

<video preload="auto" controls loop >
     <source src="slideshows/customerslideshow.mp4" type="video/mp4">
     <p>Sorry, your web browser cannot play this video.</p>
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Sorry but I don't understand your reply. If you check on you will see that I have already included the exact html that you suggest. The slide show still comes up with the error message. What I want is to publish a slide show that works on IE, FF, Chrome and Opera seamlessly. Is that possible and in what format? Thanks in advance.