[Techtalk] video editing on Linux

Almut Behrens almut-behrens at gmx.net
Sun Dec 29 17:54:37 EST 2002


On Sun, Dec 29, 2002 at 08:47:19AM +0000, Maria Blackmore wrote:
> On Fri, 27 Dec 2002, Michelle Murrain wrote:
> > converting 8mm film to digital,
> 
> You're probably going to want to do this telecine, which is basically
> projecting the film onto something and making a video recording of this,
> or filming the film.
> you can usually get attachments for a video camera to make this easy, so
> that you don't have to actually project the damn thing onto a screen
> 
> (...)
> 
> > 4) Conversion from film to video: I understand that you have to 
> > interleave new frames into a video that comes from a film because of 
> > the different frequency of the film. I couldn't find on the Cinelerra 
> > site whether or not it could do that. Does anyone know of Linux 
> > software that can do that?
> 
> If you're using telecine this will happen by itself, since you're filming
> the film.  The video camera will be running at the "correct" speed, and
> simply take a picture of whatever is in front of it, so you'll get the
> right number of frames per second out, no matter what the film is doing

just out of plain curiosity: with "telecine", are there any specific
measures taken against getting interference artifacts, as one would
normally expect when resampling already sampled, discrete data? When
not synchronized in one way or another, I'd expect to see more or
less pronounced flickering at a frequency equal to the difference
between the two original frequencies (film/camera shutter-freq.).

A simple schematic probably illustrates best what I'm having in mind:

###--###--###--###--###--###--###--###--###--###--###--###--###--###--
##--##--##--##--##--##--##--##--##--##--##--##--##--##--##--##--##--##
=   -   .   -   =   =   -   .   -   =   =   -   .   -   =   =   -   . 

The first line symbolizes what happens on the screen the film is
projected onto. '###' stands for "picture/frame visible", while '--'
denotes the pauses in between frames where the screen is dark.

The second line represents the camera. '##' denote the periods during
which the video frames are being exposed, while '--' are again the
pauses during which the camera is insensitive to exposure.

The last line indicates the expected brightness of the individual
frames taken: '=' means "frame OK", '-' stands for "frame too dark"
(due to partial exposure) and '.' are the frames which are completely
unusable, as they only got to "see" the dark screen.

This example is maybe somewhat extreme, but even with a better
frame/pause ratio, something more like

####-####-####-####-####-####-####-####-####-####-####-####-####-####-
###-###-###-###-###-###-###-###-###-###-###-###-###-###-###-###-###-##

you'd most likely still get some flickering in intensity.

It's the visual system of our brain that integrates the individual
frames into a seemingly continuous stream of light and movement.
Cameras unfortunately don't possess this ability (at least not at
present)...

Almut
(devil's advocate ;)



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