#1129557 firefox-esr: system FFmpeg backend not used, AAC/H.264/HEVC unsupported

Package:
firefox-esr
Source:
firefox-esr
Description:
Mozilla Firefox web browser - Extended Support Release (ESR)
Submitter:
Alexis Dubourg
Date:
2026-03-09 18:29:02 UTC
Severity:
normal
#1129557#5
Date:
2026-03-02 20:22:10 UTC
From:
To:
Dear Maintainer,

After recent updates on Debian Testing, Firefox ESR doesn't seem to be using system FFmpeg for media decoding anymore.

In about:support#media, Codec Support Information / Software Decoding shows:
  AAC: Unsupported
  H.264: Unsupported
  HEVC: Unsupported
As a result, websites requiring AAC, H.264 or HEVC cannot play videos.

Other codecs (VP9, AV1, Opus, Vorbis, MP3, FLAC) are supported.
ffmpeg on the system can decode AAC correctly, and ffmpeg -codecs shows AAC decoder available.

The issue has been tested on the same machine with:
  - Firefox ESR from Debian Testing, clean profile, no extensions
  - Firefox ESR from Debian Unstable
Both showed the same result: AAC/H.264/HEVC unsupported.
While Firefox ESR from Debian Stable works correctly on another machine: AAC/H.264/HEVC shown supported, videos play flawlessly.

Steps to reproduce:
1. Install firefox-esr from Debian Testing repositories.
2. Open "about:support#media".
3. Check "Codec Support Information".

Expected result:
AAC and H.264 should be supported when ffmpeg is installed.

Actual result:
AAC, H.264 and HEVC are shown as Unsupported.

Thank you for your attention,

Alex
#1129557#10
Date:
2026-03-09 18:14:51 UTC
From:
To:
#1129557#15
Date:
2026-03-09 18:26:36 UTC
From:
To:
Hi,
A workaround consists in [re]installing libavcodec61, from stable or
stable-security... as was clearly indicated by the "Versions of packages
firefox-esr recommends" section of the bug report!
In a way this bug is somewhat related to #1127569, except it seems to be
an ABI mismatch instead of a dependency problem.