Separate audio files for looping audio

[RMRattray]

Resolves: #16496 in part; this forum discussion and this one more thoroughly; this one in part

This adds the option to, when exporting audio, export the "tail", the part of the audio after the time for the last note is allotted but the music still reverberates, and the head, the part before, and the overlay of the tail over the start of the head, as three separate files. Prior to the last commit, only the tail was separated.
The mechanism for this, including naming the new files, is done in the SoundTrackWriter object with multiple encoders, rather than any higher level of abstraction, to prevent multiple calls to generateAllAudio() or modifications to higher-level abstractions of players. Much of the code changes exist to transport the separateTail flag into the audio configuration and to the mechanism for noting whether multiple files are being created.

The decision to offer two files split at the seam resolves one primary user difficulty in identifying that seam (it isn't obvious that it's hardcoded to be three seconds); and is simpler than attempting to use the mixer - or add a mechanism to the SoundTrackWriter - to overlay sound. Simplified design from @MarcSabatella 's discussion, if they'd like to weigh in here as well.

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[blackears]

Thanks for your great work on this. Is there no way, though, to automatically merge the tail into the start of the main sound buffer? Otherwise it will be necessary to open both clips in a third application and combine them that way.

[MarcSabatella]

The downside of merging it automatically would be, then you can never have a clean start. I'm imagining people would want to build audio with a clean start first, then a loop with the merged head & tail, and then end with a clean tail.

[RMRattray]

Thanks for your great work on this. Is there no way, though, to automatically merge the tail into the start of the main sound buffer? Otherwise it will be necessary to open both clips in a third application and combine them that way.

My pleasure! I'm 99% sure this would be possible, using the mixer object. I'll aim to figure that out this weekend.
Design aim: three files, tentatively:

• song-start.ogg
• song-loop.ogg
• song-end.ogg
  (I do wonder how clear "tail" is to the user, though it is the term used in the interface in the PR as-is)