Bonjour,
Le packet gstreamer0.10-ffmpeg n’est pas disponible pour Jessie, Il n’existe que pour wheezy.
L’application gnome-subtitles qui permet de sous-titrer des vidéos (surpris hein? 
) en a besoin pour pouvoir décoder des fichiers mp4 avec du h264.
Sur une de mes machines, il y a un gstreamer0.10-ffmpeg qui date de Wheezy, et qui est resté malgré la migration sous Jessie (là, je suis surpris, mais c’est un autre sujet). gnome-subtitle semble fonctionner correctement.
Sur d’autres machines que je souhaite utiliser pour cela , je n’ai pas pu installer gstreamer0.10-ffmpeg, et du coup la même vidéo n’est pas décodée.
Quelqu’un sait s’il existe un autre paquet qui le remplace ou s’il y a autre chose à faire pour avoir du mp4 décodé dans l’application gnome-subtitles ?
J’ai également jessie-backports dans mon sources.list, et j’ai installé ffmpeg , tous les plugins gstreamers qui sont dispo sous jessie ou jessie-backports.
$ dpkg -l | grep gstreamer
ii gir1.2-gstreamer-0.10 0.10.36-1.5 amd64 Description: GObject introspection data for the GStreamer library
ii gir1.2-gstreamer-1.0 1.4.4-2 amd64 Description: GObject introspection data for the GStreamer library
ii gstreamer-tools 0.10.36-1.5 amd64 Tools for use with GStreamer
ii gstreamer0.10-alsa:amd64 0.10.36-2 amd64 GStreamer plugin for ALSA
ii gstreamer0.10-gconf:amd64 0.10.31-3+nmu4+b1 amd64 GStreamer plugin for getting the sink/source information from GConf
ii gstreamer0.10-nice:amd64 0.1.7-1 amd64 ICE library (GStreamer 0.10 plugin)
ii gstreamer0.10-plugins-bad:amd64 0.10.23-7.4 amd64 GStreamer plugins from the "bad" set
ii gstreamer0.10-plugins-base:amd64 0.10.36-2 amd64 GStreamer plugins from the "base" set
ii gstreamer0.10-plugins-good:amd64 0.10.31-3+nmu4+b1 amd64 GStreamer plugins from the "good" set
ii gstreamer0.10-plugins-ugly:amd64 0.10.19-2.1 amd64 GStreamer plugins from the "ugly" set
ii gstreamer0.10-tools 0.10.36-1.5 amd64 Tools for use with GStreamer
ii gstreamer0.10-x:amd64 0.10.36-2 amd64 GStreamer plugins for X11 and Pango
ii gstreamer1.0-clutter 2.0.12-1 amd64 Clutter PLugin for GStreamer 1.0
ii gstreamer1.0-libav:amd64 1.4.4-2 amd64 libav plugin for GStreamer
ii gstreamer1.0-nice:amd64 0.1.7-1 amd64 ICE library (GStreamer plugin)
ii gstreamer1.0-plugins-bad:amd64 1.4.4-2.1+b1 amd64 GStreamer plugins from the "bad" set
ii gstreamer1.0-plugins-base:amd64 1.4.4-2 amd64 GStreamer plugins from the "base" set
ii gstreamer1.0-plugins-good:amd64 1.4.4-2 amd64 GStreamer plugins from the "good" set
ii gstreamer1.0-plugins-ugly:amd64 1.4.4-2+b1 amd64 GStreamer plugins from the "ugly" set
ii gstreamer1.0-tools 1.4.4-2 amd64 Tools for use with GStreamer
ii gstreamer1.0-x:amd64 1.4.4-2 amd64 GStreamer plugins for X11 and Pango
ii libgstreamer-plugins-bad0.10-0:amd64 0.10.23-7.4 amd64 GStreamer development files for libraries from the "bad" set
ii libgstreamer-plugins-bad1.0-0:amd64 1.4.4-2.1+b1 amd64 GStreamer development files for libraries from the "bad" set
ii libgstreamer-plugins-base0.10-0:amd64 0.10.36-2 amd64 GStreamer libraries from the "base" set
ii libgstreamer-plugins-base0.10-dev 0.10.36-2 amd64 GStreamer development files for libraries from the "base" set
ii libgstreamer-plugins-base1.0-0:amd64 1.4.4-2 amd64 GStreamer libraries from the "base" set
ii libgstreamer0.10-0:amd64 0.10.36-1.5 amd64 Core GStreamer libraries and elements
ii libgstreamer0.10-dev 0.10.36-1.5 amd64 GStreamer core development files
ii libgstreamer1.0-0:amd64 1.4.4-2 amd64 Core GStreamer libraries and elements
ii libreoffice-avmedia-backend-gstreamer 1:5.1.4~rc2-2~bpo8+1 amd64 GStreamer backend for LibreOffice
$ dpkg -l | grep ffmpeg
ii ffmpeg 7:3.0.2-4~bpo8+1 amd64 Tools for transcoding, streaming and playing of multimedia files
ii ffmpeg2theora 0.29.0~git+20140316-3 amd64 Theora video encoder using ffmpeg
ii libffms2-3:amd64 2.20-1+b1 amd64 Cross platform ffmpeg wrapper library
ii libtaoframework-ffmpeg0.4-cil 2.1.svn20090801-10 all Tao CLI binding for FFmpeg