(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:… (read more)
(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?
