MPlayer is a multimedia player that has a lot of options, but not all are available through the GUI.

Anyway, here is a list of available shortcuts that will make you able to change subtitles, audio track, sync audio and much more.

To get a list of these shortcuts, it is also possible to type man mplayer in the terminal to get the manual in text mode:

keyboard control
<- and ->
Seek backward/forward 10 seconds.
up and down
Seek forward/backward 1 minute.
pgup and pgdown
Seek forward/backward 10 minutes.
[ and ]
Decrease/increase current playback speed by 10%.
{ and }
Halve/double current playback speed.
backspace
Reset playback speed to normal.
< and >
Go backward/forward in the playlist.
ENTER
Go forward in the playlist, even over the end.
HOME and END
next/previous playtree entry in the parent list
INS and DEL (ASX playlist only)
next/previous alternative source.
p / SPACE
Pause (pressing again unpauses).
.
Step forward. Pressing once will pause movie, every con‐
secutive press will play one frame and then go into pause
mode again (any other key unpauses).
q / ESC
Stop playing and quit.
+ and -
Adjust audio delay by +/- 0.1 seconds.
/ and *
Decrease/increase volume.
9 and 0
Decrease/increase volume.
( and )
Adjust audio balance in favor of left/right channel.
m
Mute sound.
_ (MPEG-TS, AVI and libavformat only)
Cycle through the available video tracks.
# (DVD, MPEG, Matroska, AVI and libavformat only)
Cycle through the available audio tracks.
TAB (MPEG-TS only)
Cycle through the available programs.
f
Toggle fullscreen (also see -fs).
T
Toggle stay-on-top (also see -ontop).
w and e
Decrease/increase pan-and-scan range.
o
Toggle OSD states: none / seek / seek + timer / seek +
timer + total time.
d
Toggle frame dropping states: none / skip display / skip
decoding (see -framedrop and -hardframedrop).
v
Toggle subtitle visibility.
j
Cycle through the available subtitles.
y and g
Step forward/backward in the subtitle list.
F
Toggle displaying "forced subtitles".
a
Toggle subtitle alignment: top / middle / bottom.
x and z
Adjust subtitle delay by +/- 0.1 seconds.
r and t
Move subtitles up/down.
i (-edlout mode only)
Set start or end of an EDL skip and write it out to the
given file.
s (-vf screenshot only)
Take a screenshot.
S (-vf screenshot only)
Start/stop taking screenshots.
I
Show filename on the OSD.
! and @
Seek to the beginning of the previous/next chapter.
D (-vo xvmc, -vf yadif, -vf kerndeint only)
Activate/deactivate deinterlacer.

(The following keys are valid only when using a hardware accel‐
erated video output (xv, (x)vidix, (x)mga, etc), the software
equalizer (-vf eq or -vf eq2) or hue filter (-vf hue).)

1 and 2
Adjust contrast.
3 and 4
Adjust brightness.
5 and 6
Adjust hue.
7 and 8
Adjust saturation.

(The following keys are valid only when using the quartz or ma‐
cosx video output driver.)

command + 0
Resize movie window to half its original size.
command + 1
Resize movie window to its original size.
command + 2
Resize movie window to double its original size.
command + f
Toggle fullscreen (also see -fs).
command + [ and command + ]
Set movie window alpha.

(The following keys are valid only when using the sdl video out‐
put driver.)

c
Cycle through available fullscreen modes.
n
Restore original mode.

(The following keys are valid if you have a keyboard with multi‐
media keys.)

PAUSE
Pause.
STOP
Stop playing and quit.
PREVIOUS and NEXT
Seek backward/forward 1 minute.

(The following keys are only valid if GUI support is compiled in
and will take precedence over the keys defined above.)

ENTER
Start playing.
ESC
Stop playing.
l
Load file.
t
Load subtitle.
c
Open skin browser.
p
Open playlist.
r
Open preferences.

(The following keys are only valid if you compiled with TV or
DVB input support and will take precedence over the keys defined
above.)

h and k
Select previous/next channel.
n
Change norm.
u
Change channel list.

(The following keys are only valid if you compiled with dvdnav
support: They are used to navigate the menus.)

keypad 8
Select button up.
keypad 2
Select button down.
keypad 4
Select button left.
keypad 6
Select button right.
keypad 5
Return to main menu.
keypad 7
Return to nearest menu (the order of preference is: chap‐
ter->title->root).
keypad ENTER
Confirm choice.

(The following keys are only valid if teletext support is en‐
abled during compilation: They are used for controlling TV tele‐
text.)

X Switch teletext on/off.
Q and W
Go to next/prev teletext page.