post the output of 'mediainfo' utility
and
get the mplayer source:
http://www.mplayerhq.hu/MPlayer/rele...apshot.tar.bz2
now, you might need to install 'git' ( if you do not have it already ) - it will pull ffmpeg source ( mplayer dependency )
once the snapshot extracted, enter the source directory and run:
# ./configure
# make clean
# make
# make install
the new mplayer will be installed in '/usr/local/bin/mplayer' so in order to ececute the new version you will need to enter the full path, or use uninstall mplayer via apt-get or aptitude...
also, there is a few of other codec packages, that do not come with mplayer:
faad - freeware Advanced Audio Decoder player
faad2-dbg - freeware Advanced Audio Decoder - debugging symbols
libfaad-dev - freeware Advanced Audio Decoder - development files
libfaad2 - freeware Advanced Audio Decoder - runtime files
libvorbis-dev - The Vorbis General Audio Compression Codec (development files)
libvorbis0a - The Vorbis General Audio Compression Codec (Decoder library)
libvorbisenc2 - The Vorbis General Audio Compression Codec (Encoder library)
libvorbisfile3 - The Vorbis General Audio Compression Codec (High Level API)
so if you still unable to use mplayer after recompiling, get these packages, re-run ./configure, and repeat all make steps...
being able to process a 'flv' container does not mean it will be able to play all the a/v content... you still need a player that has access to the codecs ( either internal via libavcodec or external ones used during the compilation process, or shared libraries )...
without knowing what type of codec is being used in the flv, it is sometimes not easy to guess... sometimes codecs used in a container are closed source/proprietary, mediainfo should be able to give you/us some idea...