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Posted by Martin Heffels on 10/05/78 11:52
On Mon, 10 Jul 2006 15:48:55 GMT, "PTravel" <ptravel@travelersvideo.com>
wrote:
It's turning into a pissing-match ;-)
>No, it isn't. Generational loss is inevitable and progressive when duping
>analog video. Drop out is caused by physical failure of the tape and is
>neither inevitable nor likely for D-25.
I stand with it: a drop-out is severe, and not correcteable, while small,
concealed errors are the digital equivalent of generation loss. It means
that data gets changed over time. In analog the analog signal gets changed
over time as well due to continous copying. It's the same for digital.
>> Of course, the laywer that you are, we are going to have a semantics
>> battle
>> about this :-)
>
>Yes, whenever you're wrong, blame it on the fact that I'm a lawyer.
Of course :-)
>> But I use it in terms of popular semantics, which is not
>> always strictly correct for those who follow the letter of the law :-)
>
>It's inaccurate and misleading. This thread appears to have been an old one
>that someone decided to resurrect. The question appears to be, "Is there
>generational loss when duping digital video?" The answer is, "No," not,
>"Yes if you do it 100 times, as another poster has claimed."
Well, your incorrect, because there is generational loss. It's hard to
imagine if you keep think in terms of the "old world" and try to apply that
knowledge to the new world. Doesn't always work that way.
>
>>
>>>
>>>>
>>>> >> Doubt it. I do remember one test involving multiple generations of
>>>> >> recompression of DV footage which claimed degradation after about 18
>>>> >> generations, but you shouldn't see serious issues when making digital
>>>> >> copies. You're likely to have the odd dropout on the tape, but
>>>> >> otherwise the general quality should be fine.
>>>> >
>>>> >You're correct that the there will be no generation loss. However,
>>>> >drop-out
>>>> >from digital video tape is very, very rare.
>>>>
>>>> Not correct. This solely depends on the quality of the codecs used.
>>>
>>>Look up the meaning of drop out. It has nothing to do with codecs.
>>
>> We were talking about generation-loss from multiple recompression.
>
>There is no recompression at all when making a digital dupe -- whether D-25,
>mpeg, divx or whatever, as when any digital data, you can copy the file ad
>infinitum with no loss whatsoever.
Helloohhhoooooo, please read what the poster said
<quote>
I do remember one test involving multiple generations of recompression of
DV footage
</quote>
That particular paragraph above, which I left in, is not talking about
copying at all. It's talking about (let me use a different term so you will
maybe understand better) "re-rendering".
>
>> A couple
>> of years ago I tried this with the MS-DV25 codec, and after the second
>> recompression, you already saw some serious loss in quality.
>
>The thread asked about digital dupes, not recompression. Obviously,
>recompression with a lossy codec will result in generational loss.
Good, so you know that!
>I am. Drop-out within 18 dupes means a drop out rate of 5.5%. Unless
>you're storing your camera in sand, you're not going to see drop out rates
>remotely approaching that. Do you get 5.5% data loss from drop outs for
>your video?
A 5.5% rate is too high! Yes, I had that once, but that was solely due to a
bad batch of Sony DVCAM tapes.
>
>> But you're wrong anyway. You
>> won't notice the loss at all, but it's still there.
>
>By "loss," I assume you may "drop out." Because drop out is caused by a
>physical failure of the tape, you're not going to lose just one pixel on one
>frame -- drop out on digital tape is rather obvious because it effecs a
>block of data.
Yes, drop-out. Drop-out is not only caused by tape-damage, but by bad
heads, smudgy heads, tape particles flying around in a deck, electrical
interference, you name it. All these drop-outs are fortunately correcteable
on a second capture/copy-pass.
You can easily loose one pixel. Sometimes the bits are wrong, but when you
do the checksum, they still seem to be good. So, the check doesn't notice
the mistake, but your data is changed.
>I don't use a DSR1800 deck (though it would be nice to have one). I use an
>old TRV-20 consumer camcorder for transferring my miniDV to my computer (I
>fried the 1394 port on my VX2000 a couple of yearas ago). This camera puts
>out what is one the tape, and doesn't detect or fix drop outs.
Yes it does. Every deck does detect them, but you don't notice it. Only
time you notice is when the sound goes mute, because that's such a severe
drop-out, which can't be corrected anymore.
>Sorry, you're wrong. Hard disks use ECC, just like tape.
Yes, tehy do use error-correction. I'm not saying that hard-disks don't.
cheers
-martin-
--
"If he can he'll smile 'cos he's a Royal Crocodile."
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