[PS2] Keroro Gunsou: MeroMero Battle Royale (and Battle Royale Z) hidden files and file table extraction (Bandai)

[Shiruba]

These are 2 fighting games from Bandai on the PS2 based on Keroro Gunsou / Sgt Frog : https://en.wikipedia.org/wiki/Sgt._Frog#Video_games

Upon opening / mounting the ISOs on the File Explorer, nothing appears except ps2 related files (screenshots below) :

 

I think the files and the file table is hidden within the ISOs since the ISOs are 3.5GB in size. But I don't have any reverse engineering skills so maybe someone with ps2 knowledge may help me. Something important to know is that these game were released in Japan only so you may need to check the encoding first (I guess it will be Shift-JIS).

 

I can't provide download link although the game can easily be downloaded on the net.

Edited February 22 by Shiruba
title update

[morrigan]

You should treat this ISO as an archive file because it's not a standard ISO9660 file system, and some data has been hidden. Similar examples include tri-Ace's PS2 games like Star Ocean 3 and Valkyrie Profile 2.

The actual data is less than 1GB; the rest is all dummy files used for padding.

If you want to extract the audio data, I think you should learn about the PS2's PS-ADPCM encoding. It's actually very easy to identify. For example, like in the screenshot, the second column being all 00s or 02s indicates PS-ADPCM data.

You can use the software MFAudio to open the file and specify playback parameters. Once you find the correct playback parameters, you'll be able to play the audio. Make sure to note down these correct playback parameters.

Then, export these ADPCM waveform data without the file header, and manually add VAG format headers to them. Using the confirmed playback parameters, build new VAG files, which can then be played by Foobar2000 (provided you have the vgmstream plugin installed) and converted to WAV. You can Google for the VAG file header format specification.

90% of PS2 game audio data falls into two categories: PS-ADPCM and ADX. PS-ADPCM has many different file headers, representing different formats. However, regardless of the file header variations, the PS-ADPCM waveform data itself remains consistent. You can convert all of them into VAG files and then into the common WAV format.