Hi Marcus,
My name's Marcus and I'm from the UK. This is my first post.
Welcome to the list!
...
I've taken a bunch of video on my little compact camera at 30fps. Rendering it
to PAL 25fps gives the dreaded judder. I've been reading up on this and it's a
known and common problem. Having said that, is there any way in Cinelerra to
reduce the impact or cleverly disguise it?
Basically, re-rendering at a different frame rate is the same thing as
applying a slow-motion or acceleration effect on material which doesn't
match the project framerate.
With interlaced material, any time stretch effect will produce judder,
because the two fields in a frame are not treated separately. The basic
workflow is this: split interlaced material with frames-to-fields,
doubling the frame rate. Do any re-framing at that double rate (60fps to
50fps), and apply fields-to-frames afterwards.
(Cinelerra's naming is a bit confusing: frame == full frame; field ==
half frame)
Some intermediate rendering to temp files may be necessary, because the
project frame rate has to be defined correctly to make the plugins work,
but my knowledge becomes a bit blurry in this respect...
But: cinelerra usually detects the frame rate of assets automatically,
so the following might work:
Start by defining a 50fps project (!). Import your material, using the
frame-to-fields effect to convert it into 60fps half-frames. At this
point, I don't really know if cinelerra will detect all fps values
correctly. If it does, you should be able to render the file in
timing-correct 50fps. (you can render audio along with the video, if you
want. For slow-motion, you would omit the audio, naturally). If the
material becomes stretched in time, you'll need the reframeRT plugin to
convert to the new frame rate.
Import the 50fps file into a 25fps project and apply fields-to-frames to
get newly interlaced material. The judder should be gone (and be
replaced by a tiny bit of blur, I'm afraid, at the points where
interpolated lines are used instead of the original fields).
Can I ask a second question?
Again, it's a PAL thing...
I'm using the Cinelerra camera to zoom round very large photographs (and video,
above). When I set the project (via Format -> Video) to PAL 4:3 aspect ratio
it works fine and I can zoom about to my heart's content.
However, when I set it to PAL 16:9 not only does the camera's aspect ratio
change (which I would expect) but the photograph's aspect ratio changes, too;
i.e. it's all squished.
How do I set things up so that my camera is 16:9 but the photograph doesn't get
squashed? Obviously when it comes to showing it on my 16:9 widescreen TV it
needs to look right.
I think I am misunderstanding something fundamental, here, but I don't know
what! Not sure if it's my understanding of Cinelerra or aspect ratios in
general.
That's simple enough: don't count on cinelerra to do any pixel aspect
ratio correction. You'll probably want to use an external program to
batch-convert your photos to the correct pixel aspect ratio (even for
4:3, because PAL pixels are also not perfectly square...). Look at the
ImageMagick man-page of "convert", which is quite a powerful tool for
batch image conversion. You can also use Gimp with scripting, but that's
a bit more complicated... If you need more pointers, ask again, and I'll
cook a small shell script for you if you want.
Hope this helps...
Ján (from Germany)
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