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HDV and Mpeg Compression Question


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#1 Charlie Seper

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Posted 21 May 2005 - 03:28 PM

I was wondering if anyone knows exactly what codecs are used by Sony and JVC for the mpeg compression in their knew HDV cams? The stills I've seen from the two Sony models have been very impressive, but I have no idea who developed the mpeg codec they use on those cams. And, of course the JVC HD100 isn't actually out yet so we don't know much about it. I read somewhere however, that JVC developed their own codec for this model. Actually, I think JVC invented mpeg compression if I'm not mistaken. That doesn't mean that they have a great codec for it though. I really don't know.

I've used four mpeg codec engines thus far--TMPGEnc is the best I've experienced; the one built-in to Adobe Premiere (I don't know who developed it) is a close second; Ligos was a distant 3rd; and the cheesy one that comes with Roxio is so bad that its nearly unusable.

A still from TMPGEnc compared to the DV-AVI file it came from is extremely close to the original at the highest setting (8,000kbps), so at 2 to 3 times that data rate which HDV uses, ought to look fantastic. How does JVC and Sony's mpeg codec stack-up against TMPGEnc? Anybody know?

I can't check this board again for a while so, thanks in advance.
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#2 Phil Rhodes

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Posted 21 May 2005 - 04:12 PM

Hi,

> I was wondering if anyone knows exactly what codecs are used by Sony and JVC
> for the mpeg compression in their knew HDV cams?

It'll just be their own proprietary implementation of the MPEG-4 spec. Either company is big enough to have custom ASICs made to do it. However, you have realised a very important point; not all codecs are created equal, especially with advanced schemes like MPEG-4, and it is possible to do it very badly.

> The stills I've seen from the two Sony models have been very impressive, but I
> have no idea who developed the mpeg codec they use on those cams.

Sony, invariably.

> Actually, I think JVC invented mpeg compression if I'm not mistaken.

No, the Motion Picture Experts Group developed the spec. Anyone can pay to implement it and there is a "reference design" for it, which demonstrates how it's supposed to work. However, just as Premiere, Tsunami, et al, are each specific implementations, so will the one in the cameras be.

> A still from TMPGEnc compared to the DV-AVI file it came from is extremely close
> to the original at the highest setting (8,000kbps), so at 2 to 3 times that data rate
> which HDV uses, ought to look fantastic.

Yeah, but that's standard def. It's two to three times the data rate, but 1920x1080 is five times more pixels. However, Tsunami only encodes MPEG-2; the HDV implementation is MPEG-4, which is considerably cleverer - but also much harder to encode.

> How does JVC and Sony's mpeg codec stack-up against TMPGEnc?

Well as we saw above, it's not a fair comparison as Tsunami only encodes MPEG-2. However, as a general rule, hardware compressors that don't cost a six figure sum are generally pretty lacklustre. Toshiba and Hitachi make commercial MPEG-2 encoders for creating studio DVDs that cost a huge amount of money - Tsunami is probably about as good as them, but of course it's much slower. To put a hardware codec (and a hardware DV codec, plus all the other junk) in a camera, ask it to encode and decode this huge frame in realtime, to apply the complex MPEG-4 codec and then to sell it for a consumer-affordable sum... well, I fear for it, frankly!

We in the low-end world are spoiled by Tsunami; it's scarily good. Most other stuff that individuals can afford isn't nearly as well done.

Phil
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#3 Charlie Seper

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Posted 01 June 2005 - 08:16 AM

Mpeg4???

I didn't know that. In fact, I've read a couple of different articles about HDV that refer to the new cams as using mpeg2. They weren't great magazines though. I think the first time I read anything about HDV was in a consumer oriented magazine called, "Camcorder And Computer Video", that I just happened to spot the term HDV on the cover in a bookstore, so I picked it up. It definetly said Mpeg2 but given the nature of these types of magazines (geared to selling low-end cams to amateurs) it could easily have been wrong. But I know I've also seen other articles referring to HDV as using Mpeg2. Could it be that some are using Mpeg2 and others Mpeg4? I don't know anything about Mpeg4 really but I was always under the impression that it was developed for extremely low data rate transmissions i.e.--Internet and handheld computing stuff.

Thanks Phil.
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#4 Fredrik Broman

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Posted 01 June 2005 - 08:49 AM

HDV is long GOP mpeg2. Which means that a group of pictures (GOP) is compressed as one unit which makes the compression much more efficient but makes the format problematic to edit. The GOP is 15 frames which means that if you get a tape drop out you will loose all of them (not just one frame as on DV).
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#5 Phil Rhodes

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Posted 01 June 2005 - 03:39 PM

Hi,

Then I have been misinformed, but the same considerations apply.

Phil
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