Firefox on Fedora which sits in the updates [F32][F31] right now comes with enabled OpenH264 Cisco decoder for video playback and fdk-aac-free used for audio decoding.
It’s implemented by GMP (Gecko Media Plugin) API so the OpenH264 is not used through ffmpeg library but Firefox sandboxed interface, the same as Firefox uses for Widevine CDM plugin.
The OpenH264 GMP video playback is a fallback solution when system ffmpeg is missing and internal ffvpx library can’t decode the stream, so ffmpeg from RPM Fusion is always a better alternative if you can install it.
The video streams are decoded by system wide OpenH264 2.1.1 which is shipped by Fedora as mozilla-openh264 rpm package. Even if Mozilla OpenH264 (1.8.1) plugin is installed in your profile and claimed at about:plugins page, the Fedora system one is used.
You can also remove the old plugin from your profile (see Bug 1648024 for details) and with the updated Firefox packages ([F32][F31]) it won’t be installed again.
OpenH264 plugin utilization, version and playback parameters can be confirmed from GMP log, just run Firefox on terminal as:
MOZ_LOG=”GMP:5″ firefox
and look for OpenH264 version / path and so on.
Also if you find any bug during video playback (and you definitely will find one :-)), please report that at bugzilla.redhat.com or Cisco bug tracker along with the video link.
Martin Stransky's Blog 
Hi,
Thanks for this post and all the work that must have gone in to it!
I installed ffmpeg from rpmfusion as suggested but judging from the log output it is still using the fallback. Is there something else I must do for Firefox to use ffmpeg please?
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I don’t think the openh264 plugin is used when ffmpeg is installed. The plugin is just loaded but should not be used. You can run firefox on terminal as:
MOZ_LOG=”PlatformDecoderModule:5″ firefox
to verify that ffmpeg is used for actual playback.
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“ffmpeg from RPM Fusion is always a better alternative if you can install it”: Is that still true in the Fedora 33/34 timeframe?
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Yes, that’s correct.
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Hello, does OpenH264 need to be enabled from about:plugins or it works regardless of being displayed as disabled or enabled? Ty
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Hi, it should work out of the box in Fedora.
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