On Sat, 19 Sep 2009 16:19:31 +0200, Don <[email protected]> wrote:
Dear Cinelerra users,
I would like to create a horizontal scrolling of a still picture, to
create a DV (or MPEG2) interlaced PAL video at 25 images per second
(thus 50 fields per seconds, as it is an interlaced mode). The result
will be seen on a PAL television in interlaced mode.
I have tested two methods:
- I have used the Camera X parameters with keyframes.
- I have also tested the Translate effect.
The problem is that the resulting video sequence, at 25 interlaced
images per second, does not have 50 fields per seconds. I can see it, as
there is a vertical line in the still picture. With two fields in one
picture, the vertical line should have jaggy edges created by the
interlaced two fields. Unfortunately, the output of Cinelerra is a
sequence of perfect, 25 images per seconds, with no intermediate fields
computed. This result in a 'not so smooth' scrolling on the television
set.
This is the expected behaviour in Cinelerra. I agree it is not The
Right Way. Unfortunately, fixing it is not low hanging fruit.
I have specified in Cinelerra that the video is interlaced, and I have
even set interlaced flag when importing the still picture.
I think that specification only tells Cinelerra to set certain flags
in the rendered output, for the benefit of codecs and players. This
will of course _only_ work well if the pixels are never translated.
The purpose of this is to add scrolling titles to DV video recorded
during the holidays. The titles are created in Inkscape and the Gimp.
So I have two questions:
1. Is it the normal behavior of Cinelerra (not to create the two fields
when computing a translation at 25 images per second, interlaced)?
Cinelerra has only frames internally, not fields.
2. If not, could you please explain to me how to tell Cinelerra to
compute these two fields?
You would have to "upsample" the video to 50 _frames_ per second,
e.g. using "fields to frames" before you apply the translation.
Then reduce the line-doubled progressive 50Hz video back to 50i
again. Cumbersome and lossy, I know.
--
Herman Robak
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