Write: Maybe make a thing more correct
Read: Avoid accumulation of rounding errors

With a combination of audio sample rate and video frame rate that yields
a fractional number of samples per frames, the audio and video would
become desynchronised at large enough frame numbers. For example, by the
end of a 24-minute anime episode trimmed before IVTC (48 kHz, 30000/1001
fps, frame 44000), the audio could be off by over 300 milliseconds. But
not anymore.
Give each filter its own struct
Write: Die if there is more than one type of audio
Put each filter in its own file
Write: Fix the mismatch detection

Splicing audio from multiple formats is fine as long as they all decode
to the same sample type.
Write: Get the output format from the extension
Update readme.rst
Wrap readme.rst at 80 columns