Apple has added a few new articles to the Knowledge Base regarding iChat AV. Appleis Knowledge Base (sometimes referred to as the KBase) is a central location for all of Appleis support documents and other important information.

If you have used the audio or video chat features of iChat AV, you may have noticed sound only coming out of the right-hand side internal speaker of your PowerBook G4 or iBook. This is normal, and is this way to prevent audio feedback. Says Apple:

To prevent feedback from the built-in microphone and the left speaker, sound output is disabled through the left channel. When sound out is used from the internal speakers as opposed to headphones or external speakers this is far less noticeable. Because the transmission is mono sound, performance and sound quality should not be affected.

To hear sound from both channels, use headphones or external speakers (such as USB speakers). The sound through both channels, though, remains mono.

Users of certain iBook computers connected to an AirPort network may notice a popping noise occuring every ten seconds. This is due to the wireless networking interfering with the internal microphone. According to Apple:

You hear a "popping" noise every ten seconds while using an iBook, its internal microphone, and AirPort wireless networking.

[...]

Try one of these workarounds:

• Use a USB microphone
• If using an iSight camera, use iSightis built-in microphones.
• Turn off AirPort and use a wired Ethernet connection.

Note: This can also occur with third-party 802.11b wireless networks.

And finally, users behind a firewall may not be able to use iChat AVis video conferencing feature at all without opening ports in their firewall. From Apple:

To use iChat AV behind a firewall, make sure your network administrator has opened UDP port 5060.

When video conferencing, iChat AV uses four UDP ports in this range: 16384 to 16403.

For Mac OS X Firewall
The simplest workaround is to temporarily turn off the firewall in the Sharing preference pane on both computers.

To keep the Mac OS X Firewall active, follow these steps to add the necessary ports:

1. Choose Apple menu > System Preferences.
2. Choose View > Sharing.
3. Click the Firewall tab.
4. Click New.
5. Choose Other from the Port Name pop-up menu.
6. In the Port Number, Range or Series field, type in: 5060, 16384-16403
7. In the Description field type in: iChat AV
8. Click OK.

Related documents
106770 "Mac OS X: What Is a Port?"
106439 ""Well Known" TCP and UDP Ports Used By Apple Software Products"
107476 "iChat: Cannot Send or Receive a File When Firewall Is Active"