TakoTako's audio converter introduces an offset for some songs (Doppelgangers, Rokuchounen, etc.)

[vivaria]

The Doppelgangers chart plays fine in a TJAPlayer, yet the converted fumen feels like it's maybe half a second off for the entirety of the song.

[vivaria]

Some updates:

• When testing out other converted tjas in-game, I noticed that there are additional songs that suffer from this full-song offset.
• Most importantly, Rokuchounen to Ichiya Monogatari is completely out of sync.
• This is important for multiple reasons:
  • Rokuchounen is currently in my test suite, and the test makes sure that all of the ms offset values in the converted .bin file match the official fumen .bin file perfectly. (However, it's somehow still out of sync?)
  • Rokuchounen was one of the first songs I tested (very early in development), and I know for a fact that at one point, the song was synced up perfectly in-game, as I playtested it over and over.
  • Notably, this offset for Rokuchounen is also mentioned in the context of tja2bin.exe in one of the TakoTako issues:

    I found that the song starts off 200ms off

[vivaria]

Testing the very first release of tja2fumen (v0.0.1), it looks like the converted Rokuchounen is out of sync even then.

This is somewhat good news, because we can rule out any of the changes that I made between v0.0.1 and v0.5.1. However, it also means I must have gotten the song working in my manual playtests, even before I created my first release?

[vivaria]

I tried completely wiping out all of the hardcoded header byte values that I copied over from tja2bin:

https://github.com/vivaria/tja2fumen/blob/ee265327deed3ceb3e9623fdbbf18d0d03f6d7d0/src/tja2fumen/constants.py#L70-L92

However, doing so had no effect on the desync.

[vivaria]

It looks like my early manual tests for Rokuchounen occurred somewhere around https://github.com/vivaria/tja2fumen/commit/c2739b322c215ac0c725029aa8b8d8e649786c72, since it contains the following hardcoded values:

https://github.com/vivaria/tja2fumen/blob/c2739b322c215ac0c725029aa8b8d8e649786c72/tja2fumen/tja2fumen.py#L41-L43

If I checkout this commit then perform the conversion (by populating the test-data/ folder), it is still out of sync.

[vivaria]

Aha!!! I think I've figured it out.

• My early tests were actually performed by combining the converted fumen chart file with the official fumen's audio.
• If I try that again here (v0.5.1 converted fumen file, test once with TakoTako's audio and again with the official fumen audio file) there are no sync issues when using the official audio file.
• So, I think my converter works fine here -- it's TakoTako's audio handling that is introducing this ~200ms desync for some songs.

This presents quite the dilemma, since there's not really much I can do in the scope of the tja2fumen repo to fix this problem.

[vivaria]

The audio files in this case are .ogg files:

• Doppelgangers.ogg.zip
• Rokuchounen to Ichiya Monogatari.ogg.zip

But, plenty of other .ogg fumens I've tested have had their audio converted by TakoTako without any desync issues. So, I don't think it's due to the file format specifically.

Still, looking at TakoTako's OggToACB function might give us some clues.

[vivaria]

Closing this issue because the cause was identified: https://github.com/Fluto/TakoTako/issues/16#issuecomment-1636960820