This might seem redundant, but could you add BCSTM support as the input file? There's some existing BCSTM files in my Pokemon Omega Ruby rom that I want to down sample a little bit so the file size will fit. Issue is, doing so currently requires converting to wav first and I'll lose the loop points. Taking the existing BCSTM and just down sampling would be easier.
The game's BCSTM files are identicle to the ones used for themes it looks like. (they play correctly in EveryFileExplorer, just without the looping as I think that program doesn't support looping yet)
Many of the interesting music tracks though are just a tad too large in file size. Otherwise I'd just straight up put that as my bgm.bcstm file.
I'm currently using Zinnia's theme as my home menu music. Would be even more bad ass if it looped correctly.
EDIT:
For now, perhaps "importing" the loop information from an existing BCSTM would be a good compromise. Since I exported the original BCSTM to WAV and converted back unedited, the original loop point data would still be valid. This would be a much simpler solution coding wise in the mean time.