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Posted by Richard Crowley on 01/05/07 22:06
"Giraud" wrote ...
> It started when we had to get a new inexpensive
> camera. Our old TRV900 starting to show audio
> (and some video) dropouts consistently (i.e. every
> few seconds). Cleaning didn't help, and I didn't want
> to spend more money and time getting that camera
> looked at, etc.
I'll buy it from you if you don't want to get it fixed.
But I'm assuming that you are aware that model is
considered one of the best small-form DV cameras
Sony ever offered. :-)
> I started by comparing the AVI files ...
You must have "normalized" the video files so that
you were looking at the same sequence of frames,
etc. Or else you would have got an infinite number
of "differences". Can you tell us how you did that?
That seems to be one of the major roadblocks to
doing the kind of analysis that you performed.
> 1) Uncorrectable errors were frequent, even within
> one fresh tape with new equipment. I know there
> are uncorrectable errors because two captures
> produced different bits. There may have been other
> uncorrectable errors that were concealed the same
> way on the two captures, but my test would not have
> detected that.
>
> 2) Many (most?) uncorrectable errors are invisible.
> So the claim made earlier in this thread that "I did
> not see glitches, so the copy is bit-perfect" is not a
> good claim. In other words, "concealed" errors
> could very well go unnoticed but still cause bit
> differences/loss over generations.
That seems entirely consistent with the published
explanation of how the error detection/correction
works in DV.
> Most of the tape was probably copied bit-perfectly,
> but obviously not all of it. In fact, there were enough
> differences to make me call this "generational loss".
> It might go many generations before the loss becomes
> obvious, but it's still there.
Remember that with pro equipment, there is provision
for actually making bit perfect copies ("clones") where
the digital stream itself is transfered from the playback
to the record machine. Certainly no dubbing that involves
baseband/composite, Y/C or component "video" could be
"bit-perfect" as it passes from D->A and then A->D again.
> If anyone wants to look at the images I saved, let me
> know, and I could put them up on a site.
Might be instructive for the non-believers. :-)
Thank you very much for both the research and the
reporting here. You have made a very significant
contribution to the information shared here in this
newsgroup. Kudos! :-))
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