AVCHD vs HDV

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johnr
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Joined: Jan 11 2004

I appologize if this has been discussed before. I was looking at AVCHD video cameras, and found this link, http://blogs.zdnet.com/Ou/?p=998.

The author implies that due to the difficulty of creating a H.264 stream in the AVCHD, the bit rate in the consumer models is around 17 while with HDV cameras, the data rate is around 24. According to him this translates into inferior video with the AVCHD consumer cameras, probably can't be overcome. (I really can't totally follow his arguments, to be honest).

I was wondering if this is a generally known problem or is he overstating his case.?
Thanks in advance for the help.

John Rich

steve
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Joined: Apr 8 1999

Firstly, the article compares performance of two consumer cameras designed down to a cost, with lens, sensors, video processing and compression engineered to fit a works cost budget. Each of the elements of the design are specified to just do the job and not waste performance where it wouldn't contribute to overall performance. The consumer cameras are both sold on the fact that they have 1080 line images and differentiated by the cheapness of tape versus the convenience of SSD for storage. The subtleties of picture differences are probably lost on most of the target market, many of them who will use low bitrates to get more 'value' from their SSDs.
For a valid comparison between the two systems PQ, (the storage medium is largely irrelevant) the cameras need to have equal numbers of line samples (i.e. not 1920 vs 1440), lens with much better defined MTFs and complete control over the actual bitrate used on AVCHD. Its quite possible that 1920 oversampling of the 1440 cell AVCHD hardware is making the compression worse, all other things being equal.
Although I prefer HDV at the moment, I'm sure that SSD storage and something better than MPEG2 will be the way ahead, but I wouldn't regard a cheap camera as a testbed for choosing a system. In addition, test cards are fine for evaluating basic front end resolution, but both compression systems are both spatial and temporal and specifically designed to optimise compression of moving images.
I have heard here that the actaul effective compression gain of MPEG4 over MPEG2 is nowhere near 50%, something that broadcasters are now finding, and they are using serious hardware encoders that make the most out of each system.

Just my opinion.

Steve

Alan Roberts
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AVCHD delivers comparable video quality at approximately half the bit rate of HDV. the advantage is at its most when the coder uses all of the MPEG4 coding tricks, not all coders do that yet. But 17Mb/s AVCHD should be roughly equivalent to MPEG2 at between 25 and 35Mb/s. The HMC151 records AVCHD at 24mb/s and the pictures qare dramatically better than any HDV camera.

Get my test cards document, and cards for 625, 525, 720 and 1080. Thanks to Gavin Gration for hosting them.
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Mr Impact
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Joined: Feb 15 2006

Ive got a Sony Hard Drive camera that records HD in AVCHD, and the pic quality is about the same as my Canon XHA1, but while editing, it seemed to take ages to load the clips from the AVCHD format as apposed the clips captured in HDV. It also wouldnt preview them properly, whereas it does with HDV files. Are they a bigger file format, and therefore take longer to load?

I captured a complete event from the HDD camera onto my PC in 28 mins, but the editing seemed to be much slower.

fuddam
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Joined: Nov 19 2005

this is going to sound like advertising but that's only because it is:

get the trial for Sony Vegas Pro or Studio, and try the files on the timeline. I had a client using some other NLE for AVCHD files from a Sony HDD recorder, which was like pulling teeth, so I installed Vegas Studio on his pc, and it worked so well he dropped his old software (which was a new purchase) and bought the sony product.

this is all assuming you're not already using it - lol.

johnr
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Joined: Jan 11 2004

Thanks for the information. If I'm understanding correctly, AVCHD and HDV cameras take similar quality video, the only differences being in their mode of information storage in the camera and the fact that the AVCHD cameras take video in full 1920x1080 HD?

I was planning on using the Cineform I already have to convert the AVCHD files to .AVI before editing. I was wondering if Sony Vegas uses some form of intermediate codec to make editing easier.
John

infocus
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Joined: Jul 18 2003
johnr wrote:
If I'm understanding correctly, AVCHD and HDV cameras take similar quality video, the only differences being in their mode of information storage in the camera and the fact that the AVCHD cameras take video in full 1920x1080 HD?

AVC-HD as a format is capable of RECORDING a full 1920x1080 signal - whether or not the individual camera is capable of producing an output that will do it justice is quite another matter.

The quality of the image that will be seen on screen is far more a product of the front end of the camera than recording format at this market level. (To say nothing of the person behind it! :)) Hardly surprisingly, the more you pay, the better it's likely to be - irrespective of recording format.

Alan Roberts
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AVC-HD is capable of recording significantly better quality pictures than is HDV. AVC-HD, and it's big brother AVC-I, is a MPEG4 compression which takes far more computer grunt to code and to decode than does HDV which is MPEG2, but it's worth it. As Infocus says, the actual picture quality you get is very dependent on the camera itself, as much as the recording format, so it's rather hard to make exact comparisons.

NLEs can edit the footage without decoding, if they're fast enough, but it makes sense to transcode to a frame-based coder for editing. Edius does this rather well, to it's own wavelet-based HQ coder.

Get my test cards document, and cards for 625, 525, 720 and 1080. Thanks to Gavin Gration for hosting them.
Camera settings documents are held by Daniel Browning and at the EBU
My book, 'Circles of Confusion' is available here.
Also EBU Tech.3335 tells how to test cameras, and R.118 tells how to use the results.

infocus
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Joined: Jul 18 2003
Alan Roberts wrote:
AVC-HD, and it's big brother AVC-I, is a MPEG4 compression which takes far more computer grunt to code and to decode than does HDV which is MPEG2, .........

How do AVC-HD and AVC-Intra compare between themselves for computer grunt?
I assume AVC-HD is most difficult, but how does AVC-Intra compare in this respect to it and MPEG2?

Alan Roberts
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AVC-I is AVCHD, but using only the I frames. The equivalent in MOPEG is that MJPEG is MPEG2 but using only the I frames. With these I formats, you get complete stand-alone frames, just like digibeta, DV, DVCAM, DVCPRO.......

Get my test cards document, and cards for 625, 525, 720 and 1080. Thanks to Gavin Gration for hosting them.
Camera settings documents are held by Daniel Browning and at the EBU
My book, 'Circles of Confusion' is available here.
Also EBU Tech.3335 tells how to test cameras, and R.118 tells how to use the results.

infocus
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Joined: Jul 18 2003
Alan Roberts wrote:
AVC-I is AVCHD, but using only the I frames.

What I'm wondering is whether it's therefore the case that AVC-Intra needs less computer power than AVC-HD to handle - because of not having to decode the GOP structure - or whether it's the AVC nature of both of them that needs the grunt, regardless of whether it's I-frame only or long-GOP?

Alan Roberts
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It's rather more the non-uniform size of the macro blocks I reckon, although the temporal interpolation takes the same grunt as in MPEG2.

Get my test cards document, and cards for 625, 525, 720 and 1080. Thanks to Gavin Gration for hosting them.
Camera settings documents are held by Daniel Browning and at the EBU
My book, 'Circles of Confusion' is available here.
Also EBU Tech.3335 tells how to test cameras, and R.118 tells how to use the results.