Suggestions on video and sound programming tips

Hello,

I'd like to design simple audio and video playback routines for an 
application.

I've a digital signal acquired through an A/D that I'd like to play as
sound. Also I'd like to draw the signal on a window that can be streamed
through a video card with a TV output (to look like an oscilloscope.)

If there is anybody here, working on audio or video programming, I'd
like to know if you have suggestions on how to get started. E.g. audio
libraries, video libraries, video cards supported under linux, etc.

Thanks.
-- 
      Rafael