[Kdenlive-devel] Cutting List Specification Version 0.04

Sat Nov 16 18:45:03 UTC 2002

Am Samstag, 16. November 2002 18:22 schrieben Sie:
> On Saturday 16 November 2002 05:57 pm, Christian Berger wrote:
> > But NTSC doesn't have an integer fps. NTSC has 29.9something.
>
> It's 29.97... well close enough to 30.

OK, an hour of video with 29.97 fps has 107892 frames, a video with 30 fps 
has 108000 frames that's 108 frames difference, or about 3.6 seconds.
This is far less acceptable than an error of a single frame caused by 
rounding errors.

> > This is
> > already a serious problem at timecodes on normal video.
> > And look at _real_ video. You don't expect your camera or VCR to run
> > at an accuracy of better than 1% do you? And 1% equals about one frame
> > every 4 seconds. Or half a minute at a 1 hour video.
>
> What's your point? Your argument just hardens the argument te 29.97 is
> pretty close to 30. Concidering the accuracy of camera and video it _is_
> 30.

Yes, but a cutting position error of several seconds is completely 
inacceptable, and we will get that if we calculate with 30fps. Besides 
audio and video might not be in sync if we expect fixed integer framerates.

Even if we have rounding errors, those errors won't accumulate and 
therefore will be about a frame, but never more than that.

> > BTW, try to calculate the timespan between
> > 01:24:35:20 and
> > 03:32:42:01 in your head
>
> Err.. nobody want's to write the timeline XML in emacs, right? This is
> about communication between GUI and effect engine, is it? The GUI can
> have a display which could be toggled between mayby hh:mm:ss.mmm,
> hh:mm:ss.ff or just fffff (just the frame number), whatever.

Well the GUI can even have a display with framenumbers, but the cutter 
should not be given that much file-dependant information.

> > Besides without opening the files we could not even check their
> > validy. Or imagines what happens when you have a draft edit on 10 fps
> > files and later do the real edit on 25 fps files.
>
> I don't understand. Where do 10fps files come from? Why should anybody
> have a 10fps and a 25fps version of the same thing? Wouldn't you rather
> reduce resolution in your draft?

Well imagine an enviroment where you edit film digitally. For setting the 
edit you might use Video with 25 or 29.97 fps, the final edit will be done 
in 24 fps on digiticed film in batch mode (to reduce diskspace)

> > Or what is if you want to do slo-mo. Then you would maybe have to work
> > with fields. What would you do? Say it's 23,5 frames?
>
> Video _is_ frame based. slo-mo is also framebased. even if every slo-mo
> frame is an alphablend between the previous and next real frame, still a
> PAL _target_ will have 25fps, no matter how slow the slo-mo is.

Well Video is, but I suppose things like SVG aren't. And we have to 
consider all new standards. Maybe during the next few years we will get 
standards which aren't framebased.

> > Well you also have to keep in mind that computer video editing is not
> > always done with 25 fps or  30fps. Many people prefer 12,5 fps or 15
> > fps or other wiered framerates.
>
> Where is the problem with 30fps, 12.5fps, or 15fps and the hh:mm:ss.ff
> format?

Because it makes everything more complex. What if you have one second with 
5 frames another one with 10? RealMovie files might have something like 
that. Besides for example at 12.5 fps you still have the problem of some 
seconds having 12 frames the others having 12.5.
And what do you do if your VCR runs at 24 fps or maybe 27fps. Unless you 
have a VCR with capstan servo this _WILL_ happen.

> > Besides, look into the future. With new codecs interpolating frames in
> > a high quality might be trivial. Some codecs don't even have fixed
> > framerates. Just think of realplayer's codecs. They only have a
> > maximum framerate, but the actual framerate differs.
>
> I still don't get the point. Are you talking about _editing_ video in
> realplayer format? Why would you want to do that? You edit a video in a
> decnt format, i.e. DV, or if you really want to insert some stolen
> stuff, for heaven's sake in mpeg. After the job is done. You can export
> to realplayer format. (can you actually do that on linux?) If you have
> the need to edit realplayer files it is trivial to use transcode to
> transcode it to a decent format.

Well, but what if your footage is in realplayer? Transcoding it only takes 
lots of diskspace and if you use compression (even with DV) you loose even 
more quality. Besides, what makes you so sure there will never be any high 
quality variable framerate systems.

>
> Cheers,
> Rolf

Servus
  Casandro

> ***************************************************************
>  Rolf Dubitzky
>  e-mail: Rolf.Dubitzky at Physik.TU-Dresden.de
>  s-mail see http://hep.phy.tu-dresden.de/~dubitzky/
> ***************************************************************
>
>
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