man dosbox:
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SPECIAL KEYS
ALT-ENTER Go full screen and back.

ALT-PAUSE Pause emulation.

CTRL-F1 Start the keymapper.

CTRL-ALT-F5 Start/Stop creating a movie of the screen.

CTRL-F4 Swap mounted disk‐image (Only used with imgmount). Update directory cache for all drives!

CTRL-F5 Save a screenshot.(png)

CTRL-F6 Start/Stop recording sound output to a wave file.

CTRL-ALT-F7 Start/Stop recording of OPL commands.

CTRL-ALT-F8 Start/Stop the recording of raw MIDI commands.

CTRL-F7 Decrease frameskip.

CTRL-F8 Increase frameskip.

CTRL-F9 Kill dosbox.
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