Package dependencies cannot be resolved

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http://askubuntu.com – when i try to open avidio file like .mkv extension with mplayer it requires some multimedia plugin like gstreamer and and Ubuntu 12.01 freshly installed and when i tell him to install them that Error appears to me : This error could be caused by required additional software packages which are missing or not installable. Furthermore there could be a conflict between software packages which are not allowed to be installed at the same time. The following packages have unmet dependencies: gstreamer0.10-ffmpeg: Depends: libavcodec-extra-53 (>= 4:0.7.3-1) but 4:0.8.3ubuntu0.12.04 (HowTos)