Adopt YouTube's shortcuts in the web player and mobile apps.
Don't reinvent the wheel. Lots of people know these shortcuts. Use them
In the mobile app, each tap on the left of the video skips backwards 10 seconds. Tapping 4 times skips back 40 seconds.
In the desktop player, these seem to be the most useful.
Toggle play/pause - k
Rewind 10 seconds - j
Fast forward 10 seconds - l
Previous frame (while paused) - ,
Next frame (while paused) - .
Decrease playback rate - < (SHIFT+,)
Increase playback rate - > (SHIFT+.)
Seek to specific point in the video - 0..9 (7 advances to 70% of duration)
Toggle full screen - f
Close miniplayer or current dialog - ESCAPE
Toggle mute - m
If the video supports captions, toggle captions ON/OFF - c