On MIDIEND/WAVEEND/MP3END
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The on MIDIEND, on WAVEEND, and on MP3END events trigger when mIRC finishes playing a respective sound.
on <level>:MIDIEND:<commands>
Note: These events will not trigger if you use /splay to play another sound or to stop a sound being played, they only trigger if the sound finishes playing completely.
Example
on 1:WAVEEND:/echo Finished playing $filename
When a wave file finishes playing, echoes Finished playing C:\example\filename.wav.