vid_length()
{
    STATS=$(mencoder -nosound -oac copy -ovc copy -o /dev/null "$1" )
    FRAMES=$( awk 'END{print  $(NF-1) }' <<< "$STATS" )
    SECS=$( awk 'END{print  $(NF-3) }' <<< "$STATS")
    BITRATE=$(awk 'END{print  $3 }' <<< "$STATS")
}
$ time vid_length /var/cache/movies/This_Wonderful_Life-360x208.mov 2>/dev/null
real    0m1.280s

$ echo "
      Number of frames: $FRAMES frames
Number of seconds long: $SECS seconds
               Bitrate: $BITRATE kbit/s
    "
      Number of frames: 12679 frames
Number of seconds long: 848.333 seconds
               Bitrate: 161.953 kbit/s