MythTV Lirc and Mplayer

seek [type=<0/:1/:2>]
Seek to some place in the movie. Type 0 is a relative seek of +/:- seconds. Type 1 seek to % in the movie. Type 2 is a seek to an absolute position of seconds.

audio_delay
Adjust the audio delay of value seconds

quit
Quit MPlayer

pause
Pause/:unpause the playback

pt_step [force=]
Go to next/:previous entry in the playtree.

pt_up_step [force=]
Like pt_step but it jumps to next/:previous in the parent list.

alt_src_step
When more than one source is available it selects the next/:previous one (only supported by asx playlist).

sub_delay [abs=]
Adjust the subtitles delay of +/:- seconds or set it to seconds when abs is non zero.

osd [level=]
Toggle osd mode or set it to level when level > 0.

volume
Increase/:decrease volume

[contrast|brightness|hue|saturation] <-100-100> [abs=]
Set/:Adjust video parameters.

frame_drop [type=]
Toggle/:Set frame dropping mode.

sub_visibility
Toggle subtitle visibility.

sub_pos
Adjust subtitles position.

vo_fullscreen
Switch to fullscreen mode.

tv_step_channel
Select next/:previous tv channel.

tv_step_norm
Change TV norm.

tv_step_chanlist
Change channel list.

gui_[loadsubtitle|about|play|stop]

begin
remote = mceusb
prog = mplayer
button = ChanDown
config = sub_delay -1
repeat = 0
delay = 0
end

begin
remote = mceusb
prog = mplayer
button = ChanUp
config = sub_delay 1
repeat = 0
delay = 0
end

begin
remote = mceusb
prog = mplayer
button = RecTV
config = sub_visibility
repeat = 0
delay = 0
end

I picked a button I wanted for that, and checked its name with irw. Piece of cake!