The adcmd_finish command aborts (calls abortio() ) the current write
request on a channel or channels. This is useful if you have something
playing, such as a long buffer or some repetitions of a buffer, and you
want to stop it.

adcmd_finish has a flag you can set (adiof_synccycle) that allows the
waveform to finish the current cycle before aborting it. This is useful
for splicing together sounds at zero crossings or some other place in the
waveform where the amplitude at the end of one waveform matches the
amplitude at the beginning of the next. Zero crossings are positions
within the waveform at which the amplitude is zero. Splicing at zero
crossings gives you fewer clicks and pops when the audio channel is turned
off or the volume is changed.