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(AI written summary of troubleshooting steps taken before making this support thread)

Firefox version: - 152.0.1 Release - 153.0 Nightly

OS: - Windows 11 build 26200

GPU: - NVIDIA GeForce RTX 4070 SUPER

Codec package: - Microsoft HEVC Video Extensions installed from Microsoft Store

Problem

Firefox does not expose HEVC playback support, causing Twitch to disable 1440p streams encoded with HEVC.

The same machine can play the same HEVC Twitch streams in Chrome immediately after installing HEVC Video Extensions.

Expected result

Firefox should report HEVC playback support and allow playback of HEVC streams, as Chrome does on the same system.

Actual result

Firefox reports HEVC as unsupported.

about:support:

codecSupportInfo: H264 SWDEC HWDEC VP9 SWDEC HWDEC VP8 SWDEC HWDEC AV1 SWDEC HWDEC HEVC NONE

Troubleshooting already performed

- Installed Microsoft HEVC Video Extensions - Rebooted Windows - Updated NVIDIA drivers - Verified hardware acceleration is enabled - Tested with a brand new Firefox profile - Tested with Firefox Nightly - Confirmed Chrome can play the same HEVC streams

Additional observations

Chrome: - Twitch 1440p becomes available immediately after installing HEVC Video Extensions - Twitch Stats for Nerds reports:

 hev1.1.6.L150.90.0.0.0.0.0

Firefox: - Twitch reports that the browser does not support the required resolution - 1440p remains greyed out - about:support continues to report HEVC NONE

Reproducible tests

Firefox console:

MediaSource.isTypeSupported('video/mp4; codecs="hev1.1.6.L150.90"')

Result: false

MediaSource.isTypeSupported('video/mp4; codecs="hvc1.1.6.L150.90"')

Result: false

navigator.mediaCapabilities.decodingInfo({

 type: "media-source",
 video: {
   contentType: 'video/mp4; codecs="hev1.1.6.L150.90"',
   width: 2560,
   height: 1440,
   bitrate: 8000000,
   framerate: 60
 }

})

Result: {

 supported: false,
 smooth: false,
 powerEfficient: false

}

For comparison:

MediaSource.isTypeSupported('video/mp4; codecs="av01.0.08M.08"')

Result: true

navigator.mediaCapabilities.decodingInfo({

 type: "file",
 video: {
   contentType: 'video/mp4; codecs="av01.0.08M.08"',
   width: 2560,
   height: 1440,
   bitrate: 8000000,
   framerate: 60
 }

})

Result: {

 supported: true,
 smooth: true,
 powerEfficient: true

}

Additional note

Setting:

dom.media.webcodecs.h265.enabled = true

causes HTML5 codec test (https://html5test.co/) to report H.265 support, but does not change:

- about:support - MediaSource.isTypeSupported() - MediaCapabilities.decodingInfo() - Twitch HEVC playback availability

Question

Is this a known issue with HEVC Media Source Extensions support on Windows 11 build 26200, or is there another requirement for Firefox to expose HEVC playback capability through MediaSource and MediaCapabilities when the Windows HEVC codec is installed and functioning in Chromium-based browsers?

Media resource could not be decoded, error: Error Code: NS_ERROR_DOM_MEDIA_DECODE_ERR (0x806e0004) Details: virtual mozilla::MediaResult mozilla::FFmpegVideoDecoder<62>::DoDecode(mozilla::MediaRawData*, uint8_t*, int, bool*, mozilla::MediaDataDecoder::DecodedData&): avcodec_send_packet error: Unknown error occurred

Just built a new PC and using Win11. I like to have a pinned tab in Firefox playing some kind of media to have background noise. Since new build, whenever I am not 'focused' on that tab and doing other tasks, audio from that tab will cut/fade in and out.

I've been working on this for 16 hours. I've googled, binged, even yahooed. No answers. Checked and rechecked all settings, both system and browser. Uninstalled/Reinstalled *many* applications, including Firefox. My OCD won't let me rest till I have this solved.

Thanks for the help.

Fire fox is automatically playing videos/sound or both if I click on a tab that has that or also in facebook, etc. How do I stop this? I want to be able to click play when I want to hear/see something.

I've noticed that whenever I press ⌥⇧Space (option-shift-spacebar) in Firefox Developer Edition, it causes the page to refresh.

This behaviour seems to be consistent across devices.

Is there a way to change/disable this behaviour? It is very inconvenient, as it often causes me to accidentally trigger a page refresh when I type an em dash (`—`) in a text input (opt-shift-dash, and then type a space character after it, I'm very likely to hit opt-shift-space by mistake 🙈).

Facebook videos in Firefox stop playing when clicking the Windows 11 Start button or opening Solitaire (after recent update)

This issue has just started after a Windows 11 update and restart. It has never happened before. I usually watch Facebook Reels while playing Solitaire at the same time — yes, I know, I don’t have a life.

This morning, after the update and restart, I opened Facebook and started watching a Reel as normal. As soon as I clicked the Windows Start button to open the list of programs, the video stopped. I then selected Solitaire, which opened to the taskbar. I restarted the video, clicked Solitaire to open the game fully, and the video stopped again. As soon as I minimize Solitaire, the video resumes playing.

I’ve tried all the suggestions I could find via Google, but nothing has worked so far. Note that this only affects videos playing directly on Facebook — videos playing in the Windows Media Player Legacy video player itself are not affected.

Any help would be greatly appreciated… and yes, as mentioned, I clearly don’t have a life 😅 Link to video showing what happens when I select Solitaire in the Taskbar. https://drive.google.com/file/d/1oKLIl3I4f9lfTZvbU-9pJ1gMbOU7h0zm/view?usp=sharing

Regards everyone.

More info... I run two monitors and it seem if I click on whatever I have open in the second monitor the FB video stops. So something has changed after I turned my computer on this morning and updated Windows. I even did a System Restore to a setting two days before this new update and nothing changed still have the problem.

Earlier today the audio on Firefox stopped working. I have tried disabling extensions, checked output devices, reinstalled and it still doesn't work. Please Help. The Version is 150.0.1

Since the last update, I believe, because this error occurs constantly and with EVERY video. This is often, not always, the case immediately after updating FF. Now it was fine for a while, but now it's so bad that I'm having trouble watching YT videos properly. Reason: Browser open, logged in to YT. I click on a video to play - video opens, plays maybe 10 to 20 seconds, then playback stops spinning top, I also found out during the last glitch after update that if I switch the resolution briefly, higher or lower doesn't matter - important is to leave the current resolution and switch to another one. And oh wonder - immediately, instantly with the change, the video starts playing. If I wait for this - without doing anything myself, it sometimes takes 30 - 40 seconds for the video to start ... sometimes it just "hangs" ... This is extremely annoying - if it doesn't work, I have to switch browsers... What is also extremely annoying is that it occurs almost regularly after an update ... until the next one possibly, for unknown reasons, does not fix the error, but sometimes mitigates it. Now, however, the disruption/interruption is so massive and totally annoying that I'm thinking of switching. I'm just tired of it ...

• • • Translated with www.DeepL.com/Translator (free version) ***

Since the last update, I believe, because this error occurs constantly and with EVERY video. This is often, not always, the case immediately after updating FF. it was fine for a while, but now it's so bad that I'm having trouble watching YT videos properly. Reason: Browser open, logged in to YT. I click on a video to play - video opens, plays maybe 10 to 20 seconds, then playback stops spinning gyro, I also found out during the last glitch after update that if I switch the resolution briefly, higher or lower doesn't matter - important is to leave the current resolution and switch to another one. And oh wonder - immediately, instantly with the change, the video starts playing (for a while at least maybe 5 Minutes maybe 30 Sek... i´m done with FireFox ...) If I wait for this - without doing anything myself, it sometimes takes 30 - 40 seconds for the video to start ... sometimes it just “hangs” ... This is extremely annoying - if it doesn't work, I have to switch browsers... What also bothers me extremely is that it occurs almost regularly after an update ... until the next one possibly, for unknown reasons, does not fix the error, but sometimes mitigates it. Now, however, the disruption/interruption is so massive and totally annoying that I'm thinking of changing. I'm just tired of it ... Please fix it or shoot me ... any suggestions ??

Hello, I’m using Mozilla Firefox on Windows 10.

The issue happens mainly on YouTube: – Videos stutter every few seconds – Audio sometimes goes out of sync – This happens on 1080p and 720p – My internet speed is stable (~XX Mbps)

Videos in YouTube play at about 50% brightness in full screen and not full screen, unless hardware acceleration is turned off, my mouse is hovering over an auto play thumbnail, or when the video is not in full screen and I open the right click context menu on the video.

I have an AW3225QF HDR monitor and an RTX 5070ti

When listening to YouTube in the background, sound is distorted and stutters frequently, which makes it pretty much unusable. Audio is okay when Firefox is in the foreground, but as soon as I lock the phone, audio stutters appear.

I found one fix on Reddit, disabling HD sound in developer options, but I was unable to try it since nobody explained how to get to these developer options, I wasn't able to find that setting myself.

It started happening since 135, was in beta as well. I opted out of beta because of it, but it came on stable release as well so now both beta and stable versions has this issue.

Has anybody encounter that or have fix?