Install XiphQT

XiphQT Allows the playback of Ogg Vorbis (.ogg) .ogm and FLAC files.

[edit] Download

Download the latest decoder. (Make sure you download the .dmg marked 'only decoders'!)

Copy the .dmg disc image to your Apple TV

scp xiph-qt-decoders-0.1.8.dmg frontrow@appletv:

sudo hdiutil mount xiph-qt-decoders-0.1.8.dmg

The disc image will now be mounted in your /Volumes directory. eg: /Volumes/Xiph 0.1.8/

Make the file system read-write

sudo mount -uw /

Copy the Xiph components to your /Library/Components/ directory:

sudo cp -r "/Volumes/XiphQT 0.1.8/XiphQT (decoders).component" /Library/Components/

Make the file system read-only

sudo mount -ur /

Reboot your AppleTV (Is this necessary?)

sudo reboot

Update 03-Jan-2009 - After following the above steps on a 2.1 AppleTV, I had to then perform the following to get FLAC files to play in ATVFiles.

Download flac_import_0.5b1_p0.1.dmg from http://people.xiph.org/~arek/flac_import/ and transfer it over to your AppleTV using the same method as for the XiphQT dmg.

Mount it:

 sudo hdiutil mount flac_import_0.5b1_p0.1.dmg

Change into it's mounted location:

 cd /Volumes/FLAC\ Importer\ \(0.5b1\ +\ XiphQT\ patch\ 0.1\)/

Copy the contained component to your AppleTV's /Library/Quicktime directory:

 sudo cp -r FLACImport.component /Library/QuickTime/

Then restart finder or reboot your AppleTV:

 killall Finder

If you still have troubles playing your FLAC files, you might need to look at this thread for more details, check out this thread: http://forum.awkwardtv.org/viewtopic.php?f=11&t=1315