¯\_(ツ)_/¯

I'll take a shot at it. Who knows, maybe I'll get lucky.

Update, so I was able to get a new track to play in the game although my looping values were a bit off. I think I probably did pretty much what you tried, I have no idea why it worked though. So I took a .wav file of what I wanted (I did use the Chocobos of Cocoon with the Japanese lyrics in it). Ran it through the oggenc2.exe file using the batch file with a much bigger end_loop value (although it wasn't large enough I'm guessing since it cut it short in-game) which converted it into the .scd file. I then just used the ff13tools to insert the file (music_62nati_f.win32.scd) back into the game (english version - white_imgu.win32.bin). I specifically chose the english version as I was pretty sure there wouldn't be Japanese words in it. I then started up a game with a save from the beginning of Nautilus and the new music played.

The original song was an mp3, I used Audicity to convert it to a .wav (44100, 16 bit)

Let me see if I can post the link in a format that will stay. So obviously you will need to fix the host name but the download I think you want is at

world wide web dot mediafire dot com /download/065x5yy35ozg3sb/oggenc2.87-1.3.4-generic.7z

I think this is what you are looking for (batch script for using OggEnc2). The original file was called wav2scd.bat It was referenced in the 1st link. It also came with a generic SCD header. The original link was to a media fire file which Steam blocks.

oggenc2.exe -s 0 -c "LoopStart=1017856" -c "LoopEnd=4471709" "%~n1.wav"
copy /b scd.header + "%~n1.ogg" "%~n1.scd"
del "%~n1.ogg"
pause

I think I misunderstood what you wanted. Based on your post above, I have a couple of questions.

1) Are you playing the English or Japanese version of the game?
2) The track you want to use (Chocobos of Cocoon, Japanese version) already exists in the game in the Chocobo section of Nautilus, correct?
3) You would like to use this track in the early part of Nautilus rather than what they are currently using for the version of the game specified in question #1? or do you mean somewhere else?

Nothing with sound, specifically inserting new tracks for background music, special effects or voices. I would have to play with it some to try to understand how it all works.

I haven't done it myself, but I did look into it a while back and have a couple links to some information. I'm not sure if you've seen these or not.
link 1
link 2
link 3

1080p FMVs are now available on Nexusmods for both the English and Japanese language versions. 90 GB each though.

Edited to include the Japanese version.

I had this problem and found that the issue was with the version of the ffxiiicrypt tool. While it seemed to work to re-encrypt the filelist, it actually broke it. The one that works for me is dated 12/17/2015 (pretty sure), not the 2013 one.

No, it's not a cheat engine. The changes are being made to the character crystarium game data files. It's basically an extension of the Crystarium Editor mod on Nexusmods, but rather than just change the abilities to other character ones, we substituted some of the monster attacks to see which ones might work for characters. The determining factor seems to be which enemy attacks have equivalent main character animations.