public opinion poll: XDCAM vs. P2

[Bj Ahlen]

[Jan Crittenden Livingston] “If the 8 bit signal starts at 994 mbs and one algoritm delivers individual frames and a payload of 100mbs, and the other offers Groups of pictures so that your resolution is not frame independent and a payload of 35mbs, the 35mbs has more compression. You can put whatever marketing spin to this you want, the 35mbs has more compression. It is more efficient, sure, but maybe that shouldn’t be the priority when capturing the master footage.”

When you are bandwidth-constricted, efficiency is the #1 concern.

Why? Because whatever picture information cannot be reduced losslessly through efficiency, has to be compressed using DCT (Discrete Cosine Transform) and other lossy techniques that impact the picture quality.

In Long GOP formats (such as XDCAM EX), most of the stored data is frame differences.

In Intra-Frame codec formats (such as DVCPRO-HD), all of the stored data is separate frames, each of which in the case of DVCPRO-HD has to be compressed with four parallel codecs ending up with a DCT compression ratio of approximately 6.7:1.

The Long GOP format has much more space left over for picture information, so it needs much less image compression after the [lossless] data reduction of the Long GOP storage scheme.

In the case of XDCAM EX, the extra efficiency is used to a) reduce the bit rate from 100Mb/s to 35 Mb/s VBR (Variable Bit Rate), and b) store the additional resolution (1920×1080 vs. 1280×1080 for DVCPRO-HD), and c) reduce the image compression to get a sharper and more pleasant picture when there is less movement, which also happens to be when it is most needed.

The flip side is that it Long GOP is very resource intensive when editing, so it takes an up-to-date computer or rendering to a post codec.

It has been suggested that Long-GOP codecs can’t keep up with fast movement. This has been observed only in rare cases in HDV footage (less advanced codec, inexpensive DSPs), and not even in difficult circumstances (such as a tree with thousands of leaves blowing in the wind) with XDCAM.

[Jan Crittenden Livingston] “[B.J. Ahlen] “DVCPRO-HD is also limited in resolution. It maxes out at 1280×1080, while XDCAM EX as noted is a full raster codec at 1920×1080.”

You are also mistaken here. These numbers are based on the pre-filter intelligently applied to the signal prior to compression. If you look at the XDCAM HD signal coming from the 355 Sony camera the recorded footprint is 1440 X 1080. This also due to the pre-filter. Manufacturers apply this pre-filter to get rid of frequencies and details that are problematic for the algorithm. With almost 40% more signal, 1920 X 1080 XDCAM EX, vs the XDCAM HD 1440 X 1080, it still has to fit in a 35mbs payload. Numbers are easy to understand but if you don’t understand why they are what they are it can lead to the misinterpretation of the number.”

Jan, I’m confused about what you are trying to say here.

1. I said, “DVCPRO-HD…maxes out at 1280×1080, while XDCAM EX […] is a full raster codec at 1920×1080,” to which you respond “You are […] mistaken here” and then you refer to “1920 X 1080 XDCAM EX.”

So it would seem that I was not mistaken, unless I didn’t understand what you were trying to say.

2. You said, “In the Sony F355, […] the recorded footprint is 1440 X 1080 […] due to the pre-filter.” What are you referring to? The F355 has 1440×1080 CCDs, and that is what it records to blue laser disc in the camera, with wide pixels (PAR) of course. So it’s the source CCDs and a desire to keep the 1440×1080 format that determines this, not pre-filtering.

The XDCAM EX on the other hand records a 1920×1080 signal from 1920×1080 CCDs in HQ mode. The pre-filtering has no bearing on this.

Panasonic appears to prefer using internal uprezzing in most of its affordable models, which can necessitate pre-filtering before compression, while Sony cameras generally record in native resolution.

You were comparing the XDCAM HD vs. the XDCAM EX. It wasn’t clear to me exactly why, other than your point that higher resolution takes up more room.

Was your point that DVCPRO-HD would have much better picture quality in each frame because its resolution is so much lower?

Or was it just that the EX video couldn’t look nearly as good as the XDCAM HD’s because it had to fit 40% more pixels into the same 35 Mb/s bandwidth ?

Well, you have people like Jody Eldred saying that his XDCAM EX footage intercut perfectly with his F900 footage (he owns both cameras).

And finally, let me be clear that I have no connection with either Sony or Panasonic other than as a satisfied customer of high end pro gear from both.