Install Perian

This guide is basically from Nito, but it's probably useful for people not using NitoTV too. This guide assumes you will do all of the work on the Apple TV, accessing it via SSH. It has been updated for Perian 1.2.3. The QuickTime 7.6.4 update bits allow Perian to accelerate the decoding of h.264 content without compromising youtube and podcast functionality.

Installer

Installer removed in response to Apple's actions in AppleTV_OS_2.2

Manual Install

Download Perian

Download Perian_1.2.3.dmg from http://perian.org/:

wget http://perian.cachefly.net/Perian_1.2.3.dmg

Note: If you don't have wget installed, you can install it from Apple TV Binaries

Mount Read/Write

sudo mount -uw /

password: frontrow

Mount the Perian Image

hdiutil attach Perian_1.2.3.dmg

Install the Files

sudo unzip /Volumes/Perian\ 1.2.3/Perian.prefPane/Contents/Resources/Components/Perian.zip -d /Library/QuickTime/ 
sudo unzip /Volumes/Perian\ 1.2.3/Perian.prefPane/Contents/Resources/Components/CoreAudio/A52Codec.zip -d /Library/Audio/Plug-Ins/Components/
sudo unzip /Volumes/Perian\ 1.2.3/Perian.prefPane/Contents/Resources/Components/QuickTime/AC3MovieImport.zip -d /Library/QuickTime/ 

Note: If you don't have unzip installed, you can install it from Apple TV Binaries

Unmount Perian Image

hdiutil detach /Volumes/Perian\ 1.2.3

Download the QuickTime 7.6.4 Updater

wget http://appldnld.apple.com.edgesuite.net/content.info.apple.com/QuickTime/061-6742.20090909.TgQt4/QuickTime764_Tiger.dmg

Mount the QuickTime 7.6.4 Updater Image

hdiutil attach QuickTime764_Tiger.dmg

Install (only) the H264 Files

gunzip -d </Volumes/QuickTime\ for\ Tiger\ 7.6.4\ Updater/QuickTime764_Tiger.pkg/Contents/Archive.pax.gz | (cd /; sudo pax -r '*H264*')

Note: If you don't have gunzip installed, you can install it from Apple TV Binaries

Unmount QuickTime 7.6.4 Updater Image

hdiutil detach /Volumes/QuickTime\ for\ Tiger\ 7.6.4\ Updater

Mount read-only

sudo mount -ur /

Restart AppleTV

sudo reboot

Note: AppleTV must be restarted before Perian is activated. Perform this step now, or after other installations are complete. Technically you can simply kill the "Finder" process, it will be automatically relaunched and the changes will have effect immediately.