real-time VBR?

[BowlPacker]

Can someone clue me in as to how software can capture real-time to VBR MPEG? This is just something I've been wondering about. I thought the key to VBR was an initial pass through the whole source to determine how to allocate bitrate? If I am capturing to VBR MPEG on the fly (PowerVCR, MMC) how does it know how to vary the bitrate and still hit the average in the end?

[SLK001]

A "live" real-time VBR capture (I'm assuming a hardware encoder) will look more like a CBR capture for the reasons you mentioned. The encoder doesn't get more than a frame or two of advanced info on what is coming, so the bitrate will stay very close to the average bitrate. I imagine that very high-end cards could have one processor digitize the input and spool the data to memory, while another analyzes the data for the required bitrates, while still another performs the MPEG conversion and writes the results to harddisk. These types of cards are out of my price range.