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Re: 3/4" dailies without windows and curtains



Sorry to Jeff... it's me (BT) who inserted the comment about preserving
VBI.  I think you misunderstood my point- I was trying to say that there
are mechanisms that exist the DO preserve the VBI data (*), and that it is
practical because it is usually low data rate and therefore easy to
stuff somewhere in the data stream.  I did not mean to imply that it
sneaks by the compression algorithm unscathed. I would imagine that it's
especially practical in JPEG, M-JPEG and other intraframe schemes.

(*)- At least I was under the impression that this is the case; am I
just plain wrong about that?

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On Sat, 11 Jan 1997 18:11:22 -0500  Mikael Reichel wrote:
>Jeff Kreines
>"This is strange... most compression systems (JPEG and
>MPEG) preserve the VBI.  It's especially easy to do this
>since the VBI usually contains no picture info, just
>relatively low-rate data.  If it really is the case that
>even the new Avid PCI cards trash the VBI, that should be
>a firmware fix, no?
>
>Sorry Jeff, no agree.
>We are talking about "lossy " compression techniques. These rely on a succession
>of lossy and non lossy data rate reduction processes. The point is that the
>instanaeous factor of reduction from one frame to another may vary greatly. The
>greater it is reduced the greater are tricks used to render it less visible.
>These tricks would distort VBI. 
>In addition, VBI is information that is non-coherent with the actual picture
>information and therfore potentially a nuisance to have to incorporate into the
>picture coding process (motion prediction).This applies to both inter and intra
>frame coding - MPEG and JPEG. Therefor, at least in professional codecs - VBI is
>extracted and separately multiplexed into the picture datastream along with
>audio and other data. This is put back (mostly) in the right order at the other
>end. 
>
>This is one of the reasons why actual editing of interframecoded material is not
>as easy, albeit desirable. An editable "pro" MPEG format is underway though,
>hope we will enjoy seamless timecode handling for a change.
>
>Mike Reichel  
>
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>

------------------------------------------------------------
Bill Topazio, VP/Engineering     bt at mte.com   v:212-907-1225
Manhattan Transfer / Edit        New York, NY f:212-687-2719
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