How do I.T. conferences record and synchronise video, audio and slides?
It is a tall order because it requiters combining many different technologies however university I am studying at have this kind of service. 
Here is their main website: https://vips.liedm.lt/en/ 
Here is an example https://vips.liedm.lt/vflash/klientas/2204/2207/false 
Check out recorded sessions to get controls in English there is menu call "Kalba" just click it and chose English controls will change to English.

It was developed on Drupal 6 and uses technologies like Flex and flash it uses wowza and red 5 for live video streaming.