Suggestion: Framerate selection

[rawesomeawesome]

Linuxnote would need the accurate flag replaced with a framerate selector between 1,2,4,8,12,20 or 30 (default)
PPMLib would need a framespeed selector for the outputs, to set the flipnote speed.
The PPMLib change could be deferred to simply setting the speed manually in the DSi after placing the result onto the SD card.
A tiny bit of math would be required to convert the config input integer to the DSi flipnote framespeed, something like:

private byte FrameRateToFrameSpeed(int fps) => fps switch
{
    1  => 0,
    2  => 1,
    4  => 2,
    8  => 3,
    12 => 4,
    20 => 5,
    30 => 6,
    _  => 6  // default to 30
};

The encoder will need to drop or duplicate frames to match the target playback speed, effectively making output video behave like a timelapse when low FPS is chosen.
Something like: o.WithCustomArgument($"-vf fps={Config.FrameRate}");