I want to implement voice chat

There's Opus library (opus-codec.org) that is a popular simple to use speech codec library. It's designed for voice chats and can handle packet loss. I'll need help in integrating it into Xonotic. I'll likely need to know how:

• to add new dependencies to darkplaces code;
  
• to get sound from microphone (SDL 1 doesn't support recording, SDL 2 has it planned but not implemented yet);
  
• to play arbitrary sound;
  
• to sent and receive data from players.

Have you tried or done anything yet toward that goal? You're welcome to try. You'll likely have to chat with the DarkPlaces engine lead developer LordHavoc to see if he wants that in.

It is implemented in FTEqw (at least in general not sure if it uses opus), so you can probably have a look at that code and try transferring it to darkplaces.

This could be great. Opus seems to be a cutting edge technology.
I'd sure use it to sing you lullabyes while running with your flag... (okay, not quite...)