Unpack .pak files

Hey,
How does one unpack a .pak file?
NPUB31702, NPUB31672, NPUB31655 and similar games have a data-ps3.pak. The emulator seems to play some audios on these games but no video output is showed.
I'm testing with the c00 Free Demos of those games.

What are the names of the games? I'd assume that this might be a package format of the engine they're using or a proprietary file format and the extension just happens to be the same. The games should unpack all the data they need themselves, except for .sdata and .mself which are unpacked through cellFs* calls, but support for those currently is unimplemented.

NPUB31702 - Sparkle Unleashed
NPUB31672 - Tennis In The Face
NPUB31655 - Crimsonland

NPUB31702 - Sparkle Unleashed
NPUB31672 - Tennis In The Face
NPUB31655 - Crimsonland

Maybe, also in Tekken 6.Psarc file.

NPUB31702 - Sparkle Unleashed
NPUB31672 - Tennis In The Face
NPUB31655 - Crimsonland

Maybe, also in Tekken 6.Psarc file.

Forgot to mention those. This is a format that Sony offered developers to be able to compress their files in.

I know how to extract .psarc files, but .pak files aren't the same.
Already tried using the .psarc extractor with .pak files (also tried to rename from .pak to .psarc), doesn't work.

You shouldn't be extracting the game's files yourself. If the game needs those files, then it should use them itself and it should require no external help. If it doesn't help, then there's probably a bug somewhere.