DV Info Net - PDW-700 XDCAM HD Camcorder announced; 2/3rd-inch, 4:2:2

Quote:

Originally Posted by Alister Chapman (Post 745519)

I was curious about the compression ratios used for 35Mb and 50Mb so I did some maths.

4:2:0 XDCAM sampling yields 1440x1080 luma samples and 720x540 Chroma samples giving a total of 1944000 samples per frame.

4:2:2 XDCAM sampling yields 1920x1080 luma samples and 720x1080 Chroma Samples giving a total of 2851200 samples per frame.

So 4:2:2 1920x1080 sampling has 46% more data to encode. 1.46 x 35Mb gives 51.1Mb/sec.

So either the true data rate of the 50Mb system is 51.1Mb/sec with the same compression ratio or the 4:2:2 camera will be a tiny bit more compressed than the 35Mb system. I suspect the compression ratio is the same for both systems so in terms of artifacts and concatenation there should be no difference between the two systems.

Actually from my calculation just bumping up from 1440x1080 4:2:0 to 1440x1080 4:2:2 would require 50 mbits. this new format pushes it even further by also bumping up to 1920x1080.

The difference between the color alone is about 1.33 times the needed bandwidth. The extra resolution also bumps it up another 1.33x. so really the 50 mbit form of XDCAM is actually going to be compressed harder because there is so much more data there. There is about 1.78x more data while the codec is only given 1.42 more bits to work with. So if you could think of mpeg2 compression in terms of calculations (which is kind of hard) I would say 50mbit compression artifact wise would be like normal XDCAMHD at 28mbits/s. Thats still pretty darn good though if a very good encoder is used. To be honest I usually encode some pretty complex graphics at 50 mbits 4:2:2 and I never really noticed any artifacts. These graphics are rendered particle effects such as fire, explosions and dust effects.