Playback
========
LEFT and RIGHT arrows play the video in that direction at the configured FPS.
Hold SHIFT + direction to play at 10x speed.
Press COMMA or PERIOD to step one frame left or right, respectively.

Contrast
========
Contrast is controlled by rescaling the pixel intensities between a min and max threshold.
Hold UP/DOWN to change the lower threshold (increasing it blacks out dim pixels).
Hold SHIFT + UP/DOWN to change the upper threshold (decreasing it whites out bright pixels).

Events
======
LETTER keys mark the start of an event associated with that letter.
SHIFT + LETTER marks the end of the event.
Events of different types can overlap.
Delete an event initiation by terminating it at the same frame, and vice versa.

Status
======
SPACE shows in-progress events.
RETURN shows the current result table in the console.
BACKSPACE shows the current frame number and contrast thresholds in the interval [0, 1].

Prompts
=======
DELETE shows a prompt asking which in-progress event to delete, then a confirmation.
CTRL + n shows a prompt asking which in-progress event whose note to edit (if there is more than one), then the new value.

Prompts may appear in unexpected places on your screen.

Other
=====
CTRL + s to save
CTRL + z to undo
CTRL + r to redo
CTRL + h to show this message
