I managed to customize the hot keys for MPlayer finally and now it accords with my habit.
←, →: Seek
↑, ↓: Volume
Space, Mouse Left Click: Pause/Play
s: Switch subtitle
S: Enable/Disable subtitle
[, ]: Speed down/up
<, >, Ctrl+Left, Ctrl+Right: Previous/Next file at playlist
f, Mouse Left Double Click, F11: Fullscreen
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