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Tim Kolbs article on HD formats
Kudos to Tim Kolb for his article on HD formats.
However, is Tims evaluation of DVCPRO HD correct? To summarise he explains that DVCPROHD at 24fps comprises of 60% redundant frames which effectively makes the 100mbps stream into a 40Mbps stream, only marginally better than HDV at 35Mbps.
Is this a case of Tim picking the worst case example or is this true across all frame rates for both PAL and NTSC? What about 25PN?
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.
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18 Replies
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Well…does that take into account that the HDV 35Mb/s is a 1080i60 stream…So 60fps for 35Mb/s.? Opposed to DVCPRO HD’s 100Mb/s for 60fps. If you extract 24fps from an HDV stream…does that then drop it to 22Mb/s? If so…then it is STILL lower than the 40Mb/s that his math is coming up with.
Not that I am good at math..>I am a creative guy here…
Shane
Littlefrog Post
http://www.lfhd.net -
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[pom_boarder] “However, is Tims evaluation of DVCPRO HD correct? To summarise he explains that DVCPROHD at 24fps comprises of 60% redundant frames which effectively makes the 100mbps stream into a 40Mbps stream, only marginally better than HDV at 35Mbps.”
Couple of things here. DVCPRO HD is 100Mbs at 1080/60i or 720/60P. HDV at its best is 1080/60i is 25MBs not 35, this would be the XDCAM HD. Difference, One is Constant Bit Rate, HDV, and the XDCAM is Variable Bit Rate, but both at Long Groups of Pictures in their algorithm. DVCPRO compresses each frame independently, also known as Frame Independent resolution or IntraFrame Compression.
HDV or XdCam takes about 1/3 of the bit budget and applies it to the I frame and then divides evenly in CBR, and not so evenly in VBR, the number of bits per frame across each of the subsequant frames. I think you can do this math. Keep in mind that if there is a lot of motion and a lot of detail, this is handled in two ways. First the HDV algorithm decides to just loose some of the resolution, and then if that doesn’t resolve the problem of overwhelming changes, the algorithm turns blocky. I have seen it in XdCam HD even, just needs enough detail and motion.
Interestingly enough if it was just the math, the algorithms would look pretty much the same, but there is something about tying frames together in a Long GOP arrangement to gain effieciencies that tends to backfire. One of the other things that works against the HDV and XDCAM HD is the 4:2:0 color sampling vs 4:2:2.
The DVCPRO HD algorithm is 4:2:2. Each frame stands alone at a little over 1.6Mbs pre frame. If in using the PN mode of the P2 system, efficiencies are had in that it is only saving 24 frames, which if you do the math leads you to 24 independent frames with a total payload of a little under 40 Mbs.
Now if you do the math, the XDCAM HD looks like a similar number per frame but remember that it is Variable Bit Rate, to an extent, so if there is a lot of motion and a lot of detail the variable nature of the long GOP can quickly gobble up the extra bits in the first half of the GOP leaving the last half to suffer. (this is the most simplistic explanation)
Compression is more than math, it is what that is left after compression and how the individual frames are handled, the color sampling and how things are weighted. Some DVCPRO HD detractors would like to say that XDCAM HD is as good, but nothing will beat a frame independent resolution algorithm every single time.
[pom_boarder] “Is this a case of Tim picking the worst case example or is this true across all frame rates for both PAL and NTSC? What about 25PN? .”
Might be more that Tim was trying to convey something that he thought he spelled out well, but it got lost in the confusion as I think that Tim knows that DVCPRO HD is a far superior CODEC to the XDCAM HD and certainly better than HDV. So not sure what his objective was but if you came away with the idea that HDV was similar to DVCPRO HD because the number of bits used, well I think Tim perhaps failed in his mission of explaning HD formats.
I hope this helps,
Jan
Jan Crittenden Livingston
Product Manager, HPX500, HVX200, DVX100
Panasonic Broadcast & TV Systems -
[pom_boarder] “To summarise he explains that DVCPROHD at 24fps comprises of 60% redundant frames which effectively makes the 100mbps stream into a 40Mbps stream, only marginally better than HDV at 35Mbps.”
That’s a very inaccurate summarization though.
First, 1080 DVCPRO-HD is always 100 megabits. If you shoot 1080/24p (with 3:2 pulldown), 1080/25p, 1080/30p, 1080/50i, or 1080/60i, it’s always 100 megabits. In the specific case of 1080/24pA, most editing programs can strip out the duplicated “padding” frames and end up with a pure 1080/24p data stream with a net data rate of 80 megabits.
In 720 mode, each frame is stored discretely and takes up 1/60th of 100 megabits, so 24p does take up 40 megabits.
When you say “only marginally better than HDV at 35Mbps” there’s several misconceptions there. First, HDV is not 35mbps. XDCAM-HD or XDCAM-EX are, but HDV is not. HDV comes in two varieties, either 720 (at 19 mbps) or 1080 (at 25mbps). So to make a proper comparison you’d have 720/24p DV100 vs. 720p HDV, which means 40mbps vs. 19 mbps. Or you’d compare 1080/24p DV100 vs. 1080/24p HDV, so you’d have 80 mbps vs. 25mbps. Or you’d have 1080/24p DV100 vs. 1080/24p XDCAM-HD, which would be 80 mbps vs. 35mbps.
Even then, you’d have too many other variables to compare. DVCPRO-HD is always 4:2:2, HDV and XDCAM-HD are always 4:2:0, so DVCPRO-HD stores twice as much color information. But in the case of 720p, DVCPRO-HD prefilters to 960×720, whereas HDV stays at 1280×720. But, HDV uses long-GOP compression which is susceptible to variable performance depending on the situation being shot, whereas DVCPRO-HD uses consistent reliable intraframe encoding.
In short, it is impossible to compare them by the numbers. You simply cannot say that one’s number here is better than another’s number there. It ain’t that easy.
So one way you could look at it is via the manufacturer’s rankings. Sony has several flavors of HD recording systems, and they rank them like this:
#1: HDCAM-SR
#2: HDCAM
#3: XDCAM-HD
#4: HDVHDV is their lowest form of recording an HD signal. They classify XDCAM-HD as falling between HDV and HDCAM.
DVCPRO-HD is Panasonic’s direct competitor to HDCAM. It can be more fairly compared “on the numbers” to HDCAM because both are intraframe compression codecs; DVCPRO-HD records 4:2:2 color (vs. HDCAM’s 3:1:1, which means DVCPRO-HD records 50% more color info) but HDCAM has a larger bandwidth (135 megabits vs. 100 megabits). So in the end they are basically comparable.
And by that type of comparison, one can easily see that DVCPRO-HD is far superior to HDV, and is a more professional and overall better codec than XDCAM-HD. The BBC has just standardized on DVCPRO-HD for all their productions at Factual Studios and is expected to convert entirely to P2 very shortly.
Now, to confuse issues even further: the recording format is only one element in the total imaging chain. The lens, the chips, the DSP, everything all work together to produce the final image. If you chained a little $300 Handycam to a DVCPRO-HD deck and recorded straight DVCPRO-HD, and then compared that to a Sony F350 XDCAM-HD camcorder, my bet is that the XDCAM-HD recording would look much better. The final image is determined by more than just the recording format. Canon also must have believed that DVCPRO-HD was better than HDV; when they did their “watchmaker” demo footage for the XLH1, they chose to record directly through HD-SDI to an external DVCPRO-HD deck rather than use the XLH1’s own HDV deck.
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.
But the format does still come into play. A 2/3″ DVCPRO-HD camcorder would be accepted for unrestricted acquisition. A 2/3″ HDV camcorder would not.
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Right, that clears that up. …I think. Thanks very much Barry & Jan for the math lesson. 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. And in future I will describe HDV as a… What? Sub35Mbps codec? Maybe I just have a ready prepared paragraph on the complicated variations that I can just insert.
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[pom_boarder] “And in future I will describe HDV as a… What? Sub35Mbps codec?”
Well, it is a sub-35mbps codec. Nothing about HDV has anything to do with 35mbps, and never has.
Again, it comes in two flavors: HDV1, 720p-only, used only by JVC, at 19 megabits. Or HDV2, 1080-only, used by Canon and Sony, at 25 megabits. HDV does not go to 35 megabits, never has and never will.
XDCAM-HD and XDCAM-EX go to 35 megabits, but HDV doesn’t. All the flavors of HDV, XDCAM-HD and XDCAM-EX are based around the same basic thing: long-GOP MPEG-2 @ 4:2:0, so there’s room for confusion there. But if you wanted 35mbps you’d have to step up to an XDCAM-EX or XDCAM-HD product, because HDV doesn’t get anywhere near that.
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Interestingly enough, all of you point out the reason that Sony has announced an XDCAM-HD format that will run at a higher data rate, I think 50Mb/sec, and a 4:2:2. I call it XDCAM v2. When your XDCAM-SD starts out with more bandwidth than your HD version, something doesn’t smell right.
I would love it if Jan could speak to the virtues of the upcoming AVC-Intra. It looks like we’ll get the first 10-bit camcorder out of it. Before a flame starts, the Digi-Beta camcorders are 8-bit, whereas the studio decks are 10-bit.
Jan you can tell us about the new efficiencies in AVC-Intra. Also, why is it not an ideal editing codec? Is it due to the processing overhead needed?
Jeff Bernstein
Digital Desktop Consulting
Apple Pro Video VAR
XSAN Certified
MetaSAN Master Reseller323-653-7611
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[Jeff Bernstein] “I would love it if Jan could speak to the virtues of the upcoming AVC-Intra. It looks like we’ll get the first 10-bit camcorder out of it. Before a flame starts”
does not HDX-900 come with AVC-INTRA built in??
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No, and it’s not an option. The HDX900 is a tape-based camera. AVC-Intra is not a tape-based format.
HPX2000 has the option of adding the AVC-Intra card, and the HPX3000 has AVC-Intra built-in.
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