I have filed a complete index of "editable" US/UM BGM -- almost all files in the romfs/data/sound directory except for some short sound effects and cutscene sounds which are not ideal objects to edit -- see attached file.

Below is a tutorial of creating and replacing in your custom BGM. Note that it is not a new discovery, but I choose to rephrase the process in case anyone would need:
1. In Adobe Audition (or any audio format transformer you are familiar with):
· Import your source music, in "Save as" menu, change output format to .wav, 2 channel, 16bits.
· Change sampling rate to either 44100Hz for higher quality, or 32728Hz for smaller volume.
2. In BrawlBox:
· Choose drop menu "File - New - Audio - BRSTM Audio Stream" and then select your transformed material.
· Enable "Loop" and test with start & end loop points. The "*" button sets the point at current playing location, and ↑↓ buttons move it by 14 samples.
· It usually takes an initial approximate locating; then rough adjustments by ↑↓ buttons; and finally accurate tuning to gain a smooth looping.
· Encode and save to get a .brstm file.
3. In BRSTMConversionTool:
· Set "limit bytes on" according to your need in window "Quality".
· Enable "Loop start ..." (no need to imput start/end point here) in window "Loop".
· Choose a gain factor (enhance rate) in window "Volume".
- You can compare with original bcstm files for a concept of "appropriate amplitude"
- 32728Hz should generally be as load, while 44100Hz plays lower in game so should be made to sound about 50% loader.
· Transforms the .brstm to a .bcstm file.
4. Look up the Index list to find the corresponding origianl file under romfs/data/sound. Rename your .bcstm (do not mix with .brstm!) accordingly and substitude into the category.
Caution: File size of your final pack should not exceed 4GB! Disregard if you publish in the form of mod.

 

[PaiDaXing]

Nice! But it's hard to imagine how big music files make the final size of the game exceed 4G.