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Old August 14th, 2005, 03:17 PM   #1
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DV stream from HDV.... question

When I do a DV stream from a HDV camera, say into a deck, my computer, or another camera, is the signal pure DV with NO ARTIFACTS from the MPEG2? In other words is it clean and can be used as regular DV is used?

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Old August 14th, 2005, 04:20 PM   #2
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No. It is HDV on tape, which is downconverted to DV. So if there were artifacts from the original compression, they do not magically go away when converted to DV.

I would say that most HDV downconverted to DV looks great. But if you have some serious movement, you could be asking for trouble.
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Old August 14th, 2005, 09:19 PM   #3
 
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While Steve is of course correct, keep in mind that when you're downsampling, you're also getting a tighter image due to originating in HDV. Therefore, if there are small motion artifacts, they'll usually disappear, not because they're not there, but rather because of the smaller size frame not making them as easy to see.
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Old August 14th, 2005, 09:38 PM   #4
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That's true too. And it also kind of depends on how you compress it again for distribution. Maybe that eliminates the minor issues.

Just be careful with race cars and roller coasters. Any temporally compressed image is liable to give you headaches.
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Old August 14th, 2005, 10:33 PM   #5
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Hmm, first, thanks for the replies.

My use for this is to mix the footage with a Song PDX10 or PD170 as I am making a documentary. There may be a Film Transfer in the end as well, so there may be problems there with the artifacting..... do I care enough about that is the real question....
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Old August 15th, 2005, 06:47 AM   #6
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I've never been 100% clear on this, but I *think* if you shoot in DV or DVCAM mode on the FX1 or Z1, then there is no MPEG compression. In that mode DV data is written to the tape. This is different from shooting in HDV mode and using the camera to downconvert, which writes HDV to tape but sends DV over i.Link.
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Old August 15th, 2005, 01:15 PM   #7
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That is my understanding as well. Shooting in DV mode will give you only DV compression. Shooting in HDV mode will give you high-def resolution with MPEG-2 compression. If you then downconvert through the firewire, you would be downconverting MPEG-2 and then re-compressing with DV.
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Old August 15th, 2005, 01:22 PM   #8
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I just tested some high motion material and found that to be the case. If I really stress the compression by shooting scenes with massive changes from moment to moment, DV handles it a bit better than HDV. And once written to tape as HDV, the problems are there regardless of how they are captured.

But to be honest, it was difficult to find material where the material was a problem. So fast panning had to substitute for fast motion.
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