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RE: Forcing A Frames



Hello all. Dean's definition of an A frame is really quite good.I would 
simplify 
it by saying that an A frame is a two field sequence where both fields
represent the same film frame as well as sharing the same video time code
frame number.This occurs every five frames in any and all 3:2 telecine
transfers where 30 frame time code is being recorded.Obviously,making these
A frames occur on designated frames is a function of the edit controller and 
only edit controllers which control the telecine as well as the tape recorders
will work.However,the need to do so is greatly mis-understood,even among 
telecine professionals.Avid does not require such alignment,nor does 
Lightworks.In fact,all any of the popular editing systems need is an accurate
'pull-in' for each take.In other words,the editing systems need to be told 
where the A frame is.Both of the logging systems I am familiar with,Aaton 
Keylink and 
Evertz Keylog,only log A frames.Regardless of what video time code number the 
A frame falls on,these systems will give you accurate,useable numbers.
 Now here comes the other side of the story.Many editors are still convinced
that A frames occur on 0 and 5 frames.In fact,many colorists as well as other
post production pros still adhere to this  line of thinking.So,in order to log
without the use of an edit controller you must prove yourself correct.This 
means that your readers must be working perfectly and you must carefully check 
all of your data to assure accuracy.If you were using an edit controller and 
'forcing'
A frames the printed out list would be quite simple to check,as any non
conforming numbers would stand out clearly.This is how many facilities check 
their lists,by looking for non 0 and 5 edits.And this is why so many bad shot 
logs get to the end users.By assuming the non 0 and 5 edits have been logged 
incorrectly the operator ignores the reality that something has gone wrong 
somewhere along the signal paths.
 I am sorry for the long winded reply.Let me finish by saying that any of you
who does not fully understand the principals of mastering for future film cut
listing should take the time to study a bit.I talk to editors every day who
complain about the lists they get from their telecine facilities.As often as 
they are correct about the source of the problem they are actually just 
uninformed themselves.If the facility they complain about would just offer a 
good
explanation based on solid knowledge the problem would not exist.
          I wish you all happy logging.
                                                                        Randy
 

----------
From: 	Dean Humphus
Sent: 	Tuesday, October 01, 1996 9:09 AM
To: 	telecine at xyzoom.alegria.com
Subject: 	Re: Forcing A Frames



Jeff "don't wanna miss that A frame" Kreines wrote:

>What I am trying to do us use a Bosch FDL60 (w/DaVinci Classic and Keylink)
>to generate tapes and Flex files for use with either Avid Film Composers or
>Lightworks -- cutting 24 fps film for film matchback.  I believe (might be
>wrong on this) that the Avid wants the A frame to hit on a zero or five,
>timecode-wise.  
>
>So my objective is to establish where in relation to timecode the A frame
>hits, and maintain that relationship even when starting and stopping the
>teleine/recorder.
>

Jeff,

First, just to get your hopes up, daVinci used to have a 2:3 editor built
into their system and may provide what you need if  it's available for your
system.

Secondly, The A frame is defined as a sequence where an artitrary film frame
is recorded as a two field sequence, where the first field is odd dominant
and then the next film frame is recorded as a 3 field sequence (a B frame),
the C frame is a two sequence, even dominance and the the D frame is a three
field sequence even dominance.  The sequence repeats the cycle ending up at
an A frame again.  It doesn't necessarily have to be a zero or five frame,
it just has to be a multiple of five.   The tricky part is when you
terminate an edit and want to do a pickup for a continuous field sequence
and record every frame of film.  Unless you have some kind of device that
keeps track of the next tape in-point and the last film frame recorded, the
process it more miss than hit.  That is, it will be pure luck.  

 It happens to work out in a TLC-like editor that you tell the editor to
record this film frame (a hole punch on a zero KeyKode footage count e.g) to
that time code address, (usually an even numbered frame, odd dominant).   If
you decide that the sequence should start as an A-frame, then the "A" frame
will be in the gate when the editor turns on,  (don't worry about how-it's
magic).  Thereafter, the editor is responsible for determining the new
IN-point for the next edit event and will continue the unbroken sequence on
the tape.  If necessary, the editor will automatically truncate the last out
point that you manually selected to guarantee the the sequence will be
continuous.  As a matter of conveinence, you decide that the "A" frame is to
begin with an even frame, like :00 and every edit thereafter will fall on a
multiple of five, like :00, :05, :10, :15, :20, :25.    

In short, there is no way to do what you are required to do without some
kind of syncronizing device, like a TLC, ASTEC, or possibly the vintage
daVinci editor, or some other as yet unknown quantity.

Dean Humphus

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