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Tim Kolbs article on HD formats
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I wouldn
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Interesting….
how much is that option on HPX-2000? -
[Barry Green] “So you cannot judge DVCPRO-HD just by one particular camcorder. For example, Discovery HD has certified DVCPRO-HD as an acceptable production, editing, mastering, and delivery format, whereas they restrict HDV to only 15% of a program’s total content and will not accept HDV as an editing, mastering, or delivery format. However, they also put the same 15% restriction on the HVX200, even though the HVX200 shoots to one of their unrestricted acquisition formats! Why? Because there’s only so much performance one can get out of a 1/3″ camcorder, and Discovery classifies all the 1/3″ camcorders together; none of them are accepted for unrestricted acquisition.”
Barry’s post is spot-on in my opinion (not that he needs my blessing), but the paragraph above i thought was key to the idea I’m trying to convey…
Part of the status of Betacam SP in the hierarchy of imaging technology at the time was that there was no single chip, plastic lense, consumer version.
You can talk about these formats and crunch all these numbers, but I suspect that if I could get an XDcam recorder on the back of a Varicam camera head, I’d like it better than the XDcam camcorders I’ve seen even though the codec would still be XDcam. HDV doesn’t make much sense in a 2/3″ camera head design as the economics don’t really work out, but DVC ProHD on an HVX200 isn’t DVC ProHD on a larger sensor either…and I think that is the point.
I tend to lump the smaller camcorders together as far as the quality of the image is generally concerned …progressive vs interlace sensors and picture formats, the inclusion of pixel shift or not and how much (Canon has a 1440×1080 sensor in their HDV cameras, which is full raster for HDV), how much chroma subsampling is used…how much LUMA subsampling is used…temporal compression, bit rate, robustness of storage media, ease of editing…it all contributes to the overall picture.
Trying to isolate any of these factors and pick a clear winner is simply not a meaningful exercise IMO.
TimK,
Director,
Kolb Productions,Creative Cow Host,
Author/Trainer
http://www.focalpress.com
http://www.classondemand.net -
[jiri vrozina] “Interesting….
how much is that option on HPX-2000?”US MSRP of $3,000.
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[pom_boarder] “I don’t believe that many people would argue that HDV is a better codec but to find the DVCPROHD bitrate suddenly slashed by 60%, well, I’m sure a lot of users would have felt a bit miffed.”
Pom: Just to reiterate, the fact is that when you are shooting 24fps at 720p, P2 recording in PN mode does indeed have a 40 Mbit payload, that’s it. With Varicam, since you are recording to tape, you are always laying down 60fps, but if you take out the pulldown in post, you effectively end up with the same thing.
My only reason for even bringing this up is that so many times the conversation seems to focus on HDV at say, 24F on the Canon at 25 Mbits vs DVCPHD 720p24 at 100 Mbits…between users and sales types alike. The bottom line is that the codec plays only a part in the overall quality of the image, and that claiming that DVC ProHD is 100 Mbit at (up to now anyway) it’s most sought after and utilized framerate (720p24) on the Varicam and the HVX cameras simply isn’t a fair characterization. The useful payload in DVCPHD 720p24, no matter what you laid off to tape or P2, is 40 Mbits/s. It’s simply an illustration of how many factors have to really be examined when making decisions…
As Barry states, this same data reduction does not happen at 1080.
I’m not bashing Panasonic here…in fact, I thought I actually treated DVCProHD and HDcam pretty equally with the caveat that there are so many variations available in the DVCPHD world that it deserves a bit more description…
Is DVC ProHD a more robust picture recording format than HDV or XDcam? I think you’d have to conclude ‘yes’…my point is that how, or how much, it’s better may not be as cut and dried as it sometimes is presented to be.
TimK,
Director,
Kolb Productions,Creative Cow Host,
Author/Trainer
http://www.focalpress.com
http://www.classondemand.net -
[pom_boarder] “This has confused me somewhat, how can DVCPROHD be compressed 7-1 and be 40Mbs yet HDV is compressed 35-1 and be only slightly less. That would mean that HDV carries a lot more information yet we know that isn’t the case.”
Since I’m answering in the thread…I look at compression ratios a bit differently than manufacturers do. Compression ratios are usually quoted as how compressed the data set is AFTER ‘bit rate reduction’, or as Sony euphemistically states “prefiltering.”
When we refer to these resolution reductions and color subsampling, those are done BEFORE any actual “compression” takes place where there is a routine run to eliminate redundancies to optimize file size. So while perhaps 1280x720p24 4:4:4 may not compute to be 7x 100 Mbits/s, 960x720p24 4:2:2 probably does…in Sony HDcam’s case it’s a case of uncompressed being 1920x1080Psf 23.97 4:4:4 vs what is left when the footage hits the actual compression engine after “prefiltering”, which is 1440x1080PsF 23.97 3:1:1. Sony also quotes HDcam as being 7:1 compression even though uncompressed, even at 4:2:2 works out to be something on the order of 1.2 Gbits/s, making 135 Mbits/s closer to 10:1 if the comparison is done this way.
35:1 for HDV works out roughly assuming that uncompressed is something less than 900 Mbits/s, which is probably on target as HDV’s native frame size is 1440×1080, not 1920×1080, I guess that works, but then for HDcam to truly be 7:1, you could only be considering uncompressed to be slightly higher, so obviously they are starting with a 1440×1080 frame to reason HDcam’s compression ratio too…
HDV includes temporal compression (and as Jan points out, I was referring to XDcam as 35 Mbits/s not HDV) and therefore gains efficiencies. Even though all things cannot be equal, if all things WERE equal with a compression system that had two identical versions other than one version was employed temporally and spatially and one was allowed to use spatial compression alone, there IS an increased effectiveness visually with temporal compression employed. It’s still a pain to edit, no question and the robustness of the tapes and the quality of the camera heads and all that are part of it, but looking at only image quality resulting from compression, at any given bitrate, image quality would be better using temporal and spatial compression vs using spatial compression alone. It’s why temporal compression is employed for distribution…
The problem with temporal compression is that it’s hard to edit and a tape dropout (I’ve not experienced one yet, but I know it happens) is a GOP long. Combine this with the fact that for the purposes of this discussion, all the temporally compressed video we are speaking of is at a very low bitrate and the I-frame compression we’re talking about is much higher. A significant amount of the image quality differences are camera, codec design and bitrate-based as opposed to specifically temporal vs spatial compression based.
As I’ve said before, sure DVC ProHD is a better, more robust codec than HDV or XDcam, but the extent to which this is true may be more flexible than most have thought.
TimK,
Director,
Kolb Productions,Creative Cow Host,
Author/Trainer
http://www.focalpress.com
http://www.classondemand.net -
Thank You Barry.
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Tim, thanks very much for the responses and a useful article.
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