How do I extract Portal 2 sound effects?

Okay, so I have Portal 2 on my PC. I would like to use one of its sound effects for a little project, so I started searching the installed files. Well, eventually I found a bunch of "sound" files. I tried to run them, but apparently I can't.

When I go to properties, the file type says: Sound on format AU (.snd)

I don't get it (is the file .au or .snd?), how can I use such file? How could I convert it to, say, .mp3?

Solution 1:

All the sound files in the game are in the WAV format, stored within the VPK (Valve Package) files.

Use GCFScape and open up the Portal 2 content file, found at \steamapps\common\portal 2\portal2\pak01_dir.vpk (for some reason it's unlike TF2 and HL2 which use .gcf's)

There will be a directory structure visible in the program, browse to \root\sound\ and look through the subdirectories for sound effects. Some sound like throwbacks to Portal 1, and others seem like total cruft from HL2, but everything should be in there, though with perhaps confusing names.

Solution 2:

Your best bet is using VLC. Not only can it play all the waves, but it can convert them as well.

It has a convert option in the File menu.