In my last entry, I discussed the 3-way trade off between quality, size and complexity in codecs. Panasonic’s move from DVCPRO HD to AVC-Intra in their latest generation of P2 cameras provides an excellent example of a trade off between quality and complexity, as both codecs record at the same bit rate of 100mb/sec (at 30fps). How much better is AVC-Intra? To start off with, it preserves a lot more image information than DVCPRO HD. It records full raster (1920×1080, when recording 1080p) 4:2:2 at 10 bits per channel compared to 1280×1080 4:2:2 at 8 bits per channel, which means it’s starting out with almost double the data. Here’s a comparison of a frame of each (the same difference frames we looked at last time).
This is DVCPRO HD. Notice the lines around any fine detail. That’s the loss of sharp edges created by the reduction of the frame width from 1920 to 1280 pixels.
Clearly there’s a dramatic improvement in quality. So what’s the trade off? Well, I can comfortably play back DVCPRO HD footage on my old 1GHz G4 Powerbook. To play back AVC-Intra requires a nearly top-of-the line Mac Pro. It’s certainly a worthy trade off for an acquisition format, but due to its performance advantage, DVCPRO HD still makes a superior offline editing codec.
Note: While Panasonic is moving from DVCPRO to AVC-Intra, Sony is also migrating to a new generation of codecs, XDCAM and HDCAM SR. Sony’s made a different (and more complicated) set of compromises with their codecs. With XDCAM they’ve made a much more modest improvement in quality over HDCAM, but with a much higher compression ratio. With HDCAM SR, they’ve made quality the first priority (and it shows: see the difference frame from my last entry).