If you do 'live' video (display localy) than almost no CPU power is needed, only some memory bandwith. Encoding/Decoding H264 doesn't consume that much either. My experience is that if you can use the video engines (hw scaler, en/decoder H264, MPEG4, H263) you'll virtually have all CPU power left. It takes only memory bandwith.
Be aware that there is no audio compression support engine. If you are going to do audio+video you have to let the CPU do the audio compression/sync/echo cancellation.
So regarding to your 30 fps video question, you'll have all CPU power left.
Erik.
