MPV is a minimal, free and open-source video player first released in 2013. It is forked from Mplayer (first released in 2000). MPV is extensible via Lua scripts.

MPV Cheatsheet:

Basic Playback:
SPACE, p     - Play/Pause
q            - Quit
Q            - Quit and store position
LEFT/RIGHT   - Seek 5 seconds
UP/DOWN      - Seek 1 minute
,/.          - Previous/next frame
</>          - Previous/next in playlist
ENTER        - Next in playlist
Shift+l      - Loop
i            - Information panel
o            - Show playback progress

Volume:
9/0          - Decrease/increase volume
m            - Mute
/,*          - Decrease/increase volume

Playback Speed:
[/]          - Decrease/increase speed by 10%
{/}          - Halve/double speed
BACKSPACE    - Reset speed to normal

Seeking:
Shift+BACKSPACE - Undo last seek
Shift+Ctrl+BACKSPACE - Mark position

Video:
f            - Toggle fullscreen
T            - Toggle stay-on-top
A            - Cycle aspect ratio
Ctrl+h       - Toggle hardware decoding

Subtitles:
v            - Toggle subtitle visibility
j/J          - Cycle through subtitles
z/Z          - Adjust subtitle delay
r/R          - Move subtitles up/down

Audio:
#            - Cycle audio tracks
Ctrl+ +/-    - Adjust audio delay

Other:
s            - Take screenshot
S            - Screenshot without subtitles
o/O          - Show/cycle OSD
i/I          - Show/toggle stats
F8           - Show playlist
F9           - Show audio/subtitle streams
`            - Show console

Video Adjustments:
1/2          - Adjust contrast
3/4          - Adjust brightness
5/6          - Adjust gamma
7/8          - Adjust saturation

Resize Window:
Alt+0        - Half size
Alt+1        - Original size
Alt+2        - Double size