Your example video works for me.

Install the Media Feature Pack if applicable.

Does it still happen in Troubleshoot Mode?

Firefox can play .mp4 videos just fine as your example works for me.

I agree that you may need install the Media Feature Pack for your Windows if you have a N or KN edition in order to have the codecs needed.

See also https://support.mozilla.org/en-US/kb/html5-audio-and-video-firefox kb article.

Preview from the download page works, but if I save the file and open it locally, then I get a NS_ERROR_DOM_MEDIA_METADATA_ERR error in the Web Console.

Media resource file://.../videosample.mp4 could not be decoded, error: Error Code: NS_ERROR_DOM_MEDIA_METADATA_ERR (0x806e0006)
Details: static MP4Metadata::ResultAndByteBuffer mozilla::MP4Metadata::Metadata(ByteStream *): Cannot parse metadata videosample.mp4

https://bugzilla.mozilla.org/buglist.cgi?query_format=specific&order=changeddate%20desc%2Cbug_id%20desc&content=%22NS_ERROR_DOM_MEDIA_METADATA_ERR%22

I have run the video example from both Windows 10 and Windows 11 on the latest version of Firefox and it still shows the same thing. The fact you're saying "it works" installing Media Feature Pack is like putting Flex seal on a sinking boat instead of fixing it properly. Just like using a plugin to try and solve a browser problem that should have not been an issue to begin with.

Look, I run a function and it uses the browser to record video samples. That sample video I sent is from Edge recording it from there. The fact that this is not fully supported "Nativly" by Firefox is bizarre. I shouldn't need to tell someone, oh not playing? Well, install Media Feature Pack or use something that's not a Gecko engine.

See the problem? I have my own problems with Firefox as a dev sometimes with it not following basic web standards and this is one of those things.

The video is encoded by the browser on your device [phone|computer]. No way to fix this from my function with code or settings. The only way to have any browser encoded and uploaded video playable in any other browser is to re-encode the video with the h264 codec in a mpeg4 container using ffmpeg serverside. That means a VPS server, with ffmpeg and enabling the PHP shell_exec function. Just because one browser fails to follow basic web standards.

Google Drive may not have been the best place to show the sample so here, I'll do it this way. Both were recorded the same way.

Recorded from Edge: https://destructiveburn.com/DBGuest/DB/Issues/Firefox/videosample.mp4 Plays in all browsers but Firefox.

Recorded from Firefox: https://destructiveburn.com/DBGuest/DB/Issues/Firefox/videosample.webm Plays in all browsers.

I hope you understand where I am getting at. Installing extra things on the side just to get it to work is out of the question when you have multiple people who are trying to watch it but use Firefox but can't. The browser engine needs to be updated.

Preview from the download page works, but if I save the file and open it locally, then I get a NS_ERROR_DOM_MEDIA_METADATA_ERR error in the Web Console. Media resource file://.../videosample.mp4 could not be decoded, error: Error Code: NS_ERROR_DOM_MEDIA_METADATA_ERR (0x806e0006) Details: static MP4Metadata::ResultAndByteBuffer mozilla::MP4Metadata::Metadata(ByteStream *): Cannot parse metadata videosample.mp4

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https://bugzilla.mozilla.org/buglist.cgi?query_format=specific&order=changeddate%20desc%2Cbug_id%20desc&content=%22NS_ERROR_DOM_MEDIA_METADATA_ERR%22

Thanks, at least you saw the error. 😉

The fact you're saying "it works" installing Media Feature Pack is like putting Flex seal on a sinking boat instead of fixing it properly. Just like using a plugin to try and solve a browser problem that should have not been an issue to begin with.

No, the Media Feature Pack is not some lame hack or Plugin or such for Firefox users but for those who have N or KN Editions of Windows 8 or later to installed as these editions of Windows do not come with this stuff. People who have the N or KN Editions of Windows 8 or later without the media feature pack installed may have issues with playing recently uploaded videos or live streams on Youtube for example as they only had more limited codecs support.

I use Linux and one has to install FFmpeg for example in order to have the codecs to fully support including video, audio and games in html5 players used by sites all over including sites like Youtube and Twitch.