Firefox Certain audio files are not played

I have noticed that, after some recent updates, certain audio files are no longer played in Firefox. I noticed this with audio files in Whatsapp Web, but the same happens if I try to play an audio from Spotify. The playback just won’t start. I’ve opened Firefox with the terminal to see if some error is displayed there, and I’ll I could find is this series of messages

[Child 200530, MediaDecoderStateMachine #1] WARNING: Decoder=7f6805480600 state=DECODING_METADATA Decode metadata failed, shutting down decoder: file /usr/src/debug/firefox/firefox-123.0.1/dom/media/MediaDecoderStateMachine.cpp:372
[Child 200530, MediaDecoderStateMachine #1] WARNING: Decoder=7f6805480600 Decode error: NS_ERROR_DOM_MEDIA_METADATA_ERR (0x806e0006): file /usr/src/debug/firefox/firefox-123.0.1/dom/media/MediaDecoderStateMachineBase.cpp:166
[Child 200565, MediaDecoderStateMachine #1] WARNING: Decoder=7f6734126a00 state=DECODING_METADATA Decode metadata failed, shutting down decoder: file /usr/src/debug/firefox/firefox-123.0.1/dom/media/MediaDecoderStateMachine.cpp:372
[Child 200565, MediaDecoderStateMachine #1] WARNING: Decoder=7f6734126a00 Decode error: NS_ERROR_DOM_MEDIA_METADATA_ERR (0x806e0006): file /usr/src/debug/firefox/firefox-123.0.1/dom/media/MediaDecoderStateMachineBase.cpp:166

which I don’t know if they are related to my issue, but it’s all I have at the moment. Any help with debugging is appreciated.

Update: I’ve run FF in safe mode and it didn’t make a difference.

HI @MattG,

If it continues in safe mode, A.K.A. troubleshoot mode, it’s not because of any extension or something. So I suggest trying a new profile and see if that works.

Can you check this page: about:support#media if your browser supports the audio decoder?
In the table, the audio formats should be green. (theora, mp3, aac, opus, vorbis, flac, wave)

Do you remember setting anything in this about:config about hardware acceleration or something?

A new profile works. But is that a solution? Does it mean losing all my customizations?..

This might be the place to look at. Indeed, decoding for several audio formats (including mp3 and vorbis) seems to not work… How does FF handle these formats? Does it have build-in codecs or does it rely on system ones?

In about:config I haven’t changed anything related to hardware acceleration recently. I have H.A. enabled, but it’s been enabled since it was supported.

P.S. Mp3 or Vorbis files can be played in my system (outside Firefox)

There is something wrong there because every format except HEVC has software decoding support for me.

If I create a new profile the codecs seem to be there, and audio will play fine:

In about:config check for the setting media.ffvpx.enabled. If it’s set to false, change it to true, which is the default value, and see if this helps.


Yes! That was it. Super-strange regression, I have to say, but at least it was easy to fix.

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