Re: video conversion question

From: James Lindner (email suppressed)
Date: Tue Jun 06 2006 - 18:27:03 PDT

Conversions, TBC's and Preservation are something I know a little bit about.
Outputting into a quality TBC is the correct thing to do because a great
deal of time base error will be corrected as well as some of the other video
instability and chroma issues that you are likely to run into. If you are
interested in learning about a TBC that is specifically designed for
archival video and to see how it differs from a conventional one - look at
our web site ours in particular has a S-VHS in which may be useful to some
of you. What comes out of a TBC for the process outlined should be SDI with
correct blanking - and since one of the goals here is preservation - the SDI
should then be recorded on a lossless or very high quality encoded format -
DV does not fit that bill unfortunately. Since the UV space is already
compromised in Hi8 going to 4:2:2 makes good sense. you don't want to make
what you have worse.


 In fact - ALL TBC's do work "a line at a time" because that is how analog
video works - however high quality TBC's have a great deal of memory and can
store a field or more depending on the system and make corrections that way
- so each line is corrected as well as having other timing and velcomp
features that work on the line as well as the field and frame.


There is a difference between what you are calling Time Base correctors and
Frame Synchronizers. At this point in the technology - all quality devices
that are called "TBC's" are also frame synchronizers but it is important to
understand the difference. Time Base Correctors concentrate on issues
relating to errors in time base - essentially signals not showing up when
they are "supposed to" and correcting for drop outs and most TBC's are also
Proc. Amps allowing you to adjust luminance and chrominance and phase
relationships. A Frame Synchronizers job is to take a non-synchronous signal
and allow it to be gen-locked to the video system so that the timing is
brought into alignment. The classic example of a non-synchronous signal that
you want to gen-lock for use is a satellite. Video coming from a satellite
can not be "timed" from space - so a frame synchronizer takes that signal
and essentially buffers it and locks it to house timing and then clocks it
out so that it is correct. As you might imagine - there can be timing delays
when you do this - and for that reason most of the TBC's/Frame Synchronizers
sold today on the high end have a digital audio delay built in so that the
correction is made. Some TBC's built into Decks are also Frame Synchronizers
and some are not - and the feature set varies greatly as well. An outboard
system in general has a great deal more in the feature set department then
built in TBC's - otherwise why buy them?


Hi8 video was always a problematic format from an archival point of view.
The density of the recording is actually very high and the tolerances are
very tight. With audio multiplexed in the video signal - it did not take
much tracking or other error before you had a recording that lost the HQ
sound and I have worked on MANY Hi8 tapes that needed significant coaxing to
play back.


Probably more then you wanted to know.


Jim Lindner

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From: Experimental Film Discussion List [mailto:email suppressed]
On Behalf Of Cari Machet
Sent: Tuesday, June 06, 2006 7:27 PM
To: email suppressed
Subject: Re: video conversion question


yup - what he said
+ mucking around = bad


On 6/6/06, David Tetzlaff <email suppressed> wrote:

You do not want to be mucking around with buying a used TBC unless you
know exactly what you are doing. E.g. what you probably need is not a
broadcast TBC which proceses one or two lines at a time, but a
'frame-store' type which holds (natch) a whole frame at once. these are
not necessarily cheap. You should be able to borrow a working Hi8 deck
from somebody...

You say you want to preserve 4;2;2 colorspace. What digital format, then
are you looking to convert to (DVC Pro 50??) how are you you going to
post-produce the material (if at all), and what is the destination. If you
just want to project the tapes and you put them in any 4;2:2 digital
format, you'll need access to a deck in that (quite expensive) format to
play them back, and if you're going to DVD, I'm not aware that the 4;2;2
vs. 4:1:1 difference would be significant next to the MPEG-2 compression
in any affordable DVD authoring program.

It strikes me that a moe sensible approach would just be to find someone
who can dub the tapes from Hi8 to DV, and test out the results. This
should cost next to nothing: If It's only a tape or two I could probably
do it for you for the cost of shipping and tape, as my school lab has a
hi8 deck in our dub rack.

A lot depends on the quality of the Hi8 source tapes. Analog tapes can
deteritorate a lot over the years...

For info on FrameWorks, contact Pip Chodorov at <email suppressed
<mailto:email suppressed> >.


__________________________________________________________________ For info
on FrameWorks, contact Pip Chodorov at <email suppressed>.

For info on FrameWorks, contact Pip Chodorov at <email suppressed>.