I'm interested in video conferencing and content sharing at the same time. How is the whole thing made? From what I've found in the internet I saw that the protocol that is used is H.239 over H.323, but basically that's all I found.
Are there several types of sharing content? Are the voice and video sharing the same stream with the content? Is the content available only on another screen or it can be mixed with the video in the same screen? Is there a place where can see a sample call flow of the whole operation?
The basics of content sharing AKA H.239: http://en.wikipedia.org/wiki/H.239.
The official text of ITU-T Recommendation H.239: http://www.itu.int/rec/T-REC-H.239/en.
As 'people' and 'content' video streams are transmitted separated in different logical channels it's up to receiving site how to display the streams.
There is no special description for audio in H.239, in Polycom's implementation the 'people' and 'content' audio streams are mixed.