To zoom mplayer, pass the -zoom option along with -x and -y options::
$ mplayer -zoom -x 640 -y 480 file.mpg
Getting help for a given option (like -vo)
To get help for some options, you need to specify help after the help flag. -vo example::
$ mplayer -vo help
will tell you all the video output drivers.
Output a audio file with mplayer
You might be hearing a stream from the internet or another media and just
wants to output it to a WAV file. Just use the
mplayer -ao pcm:file=output.wav file.mp3
Later, you might want to convert it to mp3 (with Lame_, for instance) or another forma.
How to convert any video or audio to WAV using mplayer - VideoHelp Forum
Increasing volume by software
-softvol options. The first controls the
limit of the software amplification. The later controls the starting volume.
Enable subtitle using external file
Just use the
-sub option, passing the subtitle file as parameter.
If you are running a high quality video like 1080p, mplayer can tell you your
system is too slow to play it. There can be several workarounds for this, as
found in the internet. One that worked for me was using the
video - MPlayer: your system is too slow to play this! - Ask Ubuntu