Subject: Re: bug#77559: mullvadbrowser & torbrowser can’t play AAC LATM streams

From: André Batista <[email-masked]>
Date: Thu, 29 May 2025 18:26:36 -0300

Hi Ian,

sáb 05 abr 2025 às 11:51:21 (1743864681), [email-masked] enviou:
> When testing patches for #77460 and #77461, I noticed that neither mullvad
> nor torbrowser can play live videos.  ex. if you launch either browser,
> navigate to youtube.com, search "live" and click on any video with the red
> "live" badge, you get a "Your browser can’t play this video" error.
> 

Is there another way to test this besides going to youtube?

Also, is this a guix only thing?  AKA, have you tried other versions
of these browsers elsewhere with different results?

The way you describe the issue makes me wonder if this is related to
youtube, tor/mullvad browsers or guix.

> If I launch Mullvad from a shell, I see this output:
> 
> [Child 22618, MediaDecoderStateMachine #1] WARNING: Decoder=7efdca045b00
> Decode error: NS_ERROR_DOM_MEDIA_FATAL_ERR (0x806e0005) - Error no decoder
> found for audio/mp4a-latm: file /tmp/guix-build-mullvadbrowser-14.0.7.drv-0/firefox-mullvad-browser-128.8.0esr-14.0-1-build2/dom/media/MediaDecoderStateMachineBase.cpp:167
> 
> This seems related to #72265, which was a report about LibreWolf not
> enabling hardware acceleration for video decoding; after applying the
> provided patch, the same problem resulted.  I think the same situation is
> happening with these browsers.  I don’t have a satisfying fix; LW still has
> no hwaccel support, and neither does Firefox in nonguix.
> 

Sorry but I'm confused here: you mean, without that patch LW could play
these streams, but after applying it cannot?  Or did you create a local
version of the browsers in question with the same patch and got no
luck?

I may be in the wrong here, but isn't hardware acceleration privacy
sensitive in the context of these browsers?  Meaning it could be used
to fingerprint users based on the hardware they have available.

> Mullvad’s about:support claims AAC is supported with hardware acceleration.
> LATM is a container format[1], not a codec, and doesn’t show up anywhere on
> that page.  Per the FFmpeg changelog, LATM support was added to in version
> 0.9(!), and doesn’t appear to have a configure flag to control whether it’s
> enabled or not.  So it’s not clear to me why Firefoxen aren’t able to decode
> these streams.
> 

Do they currently work on LibreWolf though?

Cheers!