[rafalaos] “We have been talking about XDCam, and I always thought XDCam is 422 with 18-25-35Mbps. “
Sorry but that’s incorrect.
XDCAM HD is currently 4:2:0 @ 18mb VBR, 25mb CBR, and 35mb VBR.
The forthcoming XDCAM EX camera will not have the 18mb mode, but will offer 720P and have a full 1920×1080 pixel count imager. The current XDCAM HD cameras have a 1440×1080 chip.
The only XDCAM HD camera that can RECORD 4:2:2 is the forthcoming PDW-700 with 2/3 CCDs and a 50mb recording rate.
However, as was stated, if you take a LIVE FEED from the camera via HDSDI, you bypass the chroma subsampling and MPEG compression. This signal runs at around 1.4 Gb/second. This applies to several cameras on the market such as the full sized XDCAM HD F350, The Canon XLH1 and XHG1, and the JVC Pro HD 250.
Don’t get so hung up on the 4:2:0 thing because this isn’t like SD and there is quite a bit of chroma information in progressive mode. People have been pulling very nice keys with the 4:2:0.
The variable bit rate helps most with storage requirements per frame, but contributes to quality indirectly because it allows a higher maximum bitrate without eating up all your storage. The 35mb data rate allows for better motion compensation, etc and that is why XDCAM HD looks better than HDV in high motion scenes.