I confirm, you are fully right, it's ffmpeg from Marillat which depends
on libavcodec52 which itself depends on libva1 (without version) but
actually relies on an older version of libva1, provided by
debian-multimedia.org but hidden by a new version from Debian.
Fix in case someone reads these lines: downgrade libva1 to an older
sudo aptitude install libva1=0.31.0-0.0+sds12
Sorry for the noise,
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