The MSN protocol supports Audio/Video chatting.
Unfortunately, there are at least five different protocols that allows you to do this, each implementing a different type of A/V chat.
The Audio/Video conversation
The 'old style' audio/video conversation is a feature that allows bidirectional Audio and optionally Video streaming.
It is an old protocol that is not used anymore in WLM but is still there for keeping that feature interoperable with the windows messenger product still running on MSNP9.
This protocol is compatible with netmeeting and gnomemeeting.
For more information : Audio Video conference
The Video Call
The 'Video Call' feature is a bidirectional Audio and Video conversation which relies on the MSNP2P protocol for the signaling.
The video frames use the WMV3 video codec and the audio frames use the Siren codec.
The video and audio frames are interlaced
For more information : Video Call
The 'Webcam' feature is a unidirectional Video only conversation which relies on MSNP2P for the signaling.
The Video frames are encoded with the ML20 codec.
The only difference between this feature and the 'Video Call' feature in terms of protocol is the 'Context' field of the MSNP2P invite and the actual data being sent and received.
For more information : Webcam
The Computer Call
The 'Computer Call' feature is a bidirectional Audio only feature which uses SIP and RTP for the signaling.
It supports multiple codecs which are to be negociated during the SIP invite using the SDP payload.
The codecs officially supported by WLM are :
For more information : Computer call
The Voice clips
The 'Voice clips' feature is a unidirectional audio clip.
It relies on the MSNP2P protocol for transferring the audio clip and use the Siren codec.
The 'Voice clips' are WAV/RIFF files encoding with the Siren codec and have a maximum of 15 seconds in length.
For more information : Voice clips