I know MP3 is out, and ADPCM won't play backwards. I tried "unsigned 8-bit PCM" for the heck of it, and it works.
But is there a recommended second-best if not using ADPCM?
TIA!
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PCM is the only option currently. ADPCM encodes a block of samples at a time, so we'd need a mechanism for buffering each block before playback; doable, but a lot of fussy work for a pretty niche case. For mp3 we'd have to decode the entire file to a PCM buffer--its blocks aren't self-contained like ADPCM, each one depends on data from the previous, so there's no good way to walk it backwards.
I recall that I was looking into implementing negative rate playback for fileplayers, and there's a similar buffer-juggling problem there, even for PCM data. If I ever do implement that I expect it'd provide a solution for ADPCM playback too. But again, lot of work for very niche use case!
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Thanks. I choose well by chance, then!
I don't think expanded reverse-rate support would make much difference in my case other than total app storage size. Definitely don't bother doing any any special work!