ffmpeg depends on libmfx-gen1.2 on Alder Lake for Intel QSV support

[Bjorn Toft Madsen]

On Intel 12th gen CPUs (Alder Lake), ffmpeg requires package libmfx-gen1.2 to use QSV hardware decoding/encoding, but it's not marked as a dependency and therefore not installed with ffmpeg.

As stated on https://github.com/Intel-Media-SDK/MediaSDK#media-sdk-support-matrix, ADL-S, ADL-P and future Intel CPUs are not supported by libmfxhw64.so.1. When h264_qsv is used as a decoder or encoder, without libmfx-gen1.2 installed, ffmpeg exits with error:
Error initializing an internal MFX session: unsupported (-3)

This is because the libmfx.so.1 dispatcher wants to dispatch to libmfx-gen.so.1.2 for the Intel Quick Sync Video support, but can't due to the missing shared library.

When libmfx-gen1.2 is installed, the dispatcher succeeds and the QSV usage occurs.

It seems to me that libmfx-gen1.2 should be marked as a dependency (possibly as a dependency of libavutil56, of which ffmpeg depends) to ensure QSV hardware can be used on Alder Lake architectures, and beyond, without users figuring this out themselves.

ProblemType: Bug
DistroRelease: Ubuntu 22.04
Package: ffmpeg 7:4.4.1-3ubuntu5
Uname: Linux 5.17.0-051700-generic x86_64
ApportVersion: 2.20.11-0ubuntu82
Architecture: amd64
CasperMD5CheckResult: pass
Date: Wed Apr 27 16:08:12 2022
InstallationDate: Installed on 2022-04-22 (5 days ago)
InstallationMedia: Ubuntu-Server 22.04 LTS "Jammy Jellyfish" - Release amd64 (20220421)
ProcEnviron:
 TERM=xterm-256color
 PATH=(custom, no user)
 XDG_RUNTIME_DIR=<set>
 LANG=en_US.UTF-8
 SHELL=/bin/bash
SourcePackage: ffmpeg
UpgradeStatus: No upgrade log present (probably fresh install)

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.

[Sebastian Ramacher (s-ramacher)]

This sounds more like a bug in libmfx1.