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