In game:
1) click "~" for console
2) write command: ";record" if correct, you see big red dot in right
3) ";stoprecord" stopt record demo
4) recorded demo saved in "Tremulous\base\demos\demo0000.dm_69"
5) see recorded demo in game: "~" and command: ";demo demo0000"
You can also record in *.avi
1) for console: "~"
2) command: ";video" start record
3) command: ";stopvideo" stop record
4) video saved in "Tremulous\base\videos\video0000.avi"
5) but be carefully, this mode generated big filesize