When is 29.97 fps appropriate and how to address specific scenarios

[franciscola]

The overwhelming majority of NTSC DVD video is encoded at 29.97 fps, but nearly all are either telecined or interlaced and best processed at either 23.976 or 59.94. Is there any scenario when the video should actually be processed at 29.97, aside from the occasional progressive DVD video?

There are two specific scenarios that I'm most curious about. The first is something I've run into with videos that were originally PAL and later converted to interlaced NTSC (the Crime Inc sample). If I deinterlace this video and use 59.94 fps, I get the sense that nothing is gained from the increased framerate and that I just needlessly created a bunch of duplicate frames. Is 59.94 fps appropriate for cases like this or should I leave it at 29.97 after deinterlacing?

The second is a case of progressive DVD video at 29.97 fps (the Baka sample). Even though this video is progressive, it's full of judder and duplicate frames, so I'm assuming that someone screwed up and either deinterlaced a telecined video or screwed with the original framerate to meet DVD specs. Are cases like this a lost cause or should you try to get rid of the duplicate frames and return it to its original framerate, in effect treating it like telecined video?

[Selur]

Here's my train of thoughts about this:

What is the original frame rate here? (When folks mix different content with different frame rates, scan types, etc. strange things happen,... )
In general, the question is: What is your goal? and in what time frame do you need to get to it sometimes you know a better, but too slow way. (scene-by-scene filtering, finding correct patterns per scene and re-doing authoring decisions is usually not in the time/motivation 'budget')
Whether something is appropriate or not depends on what you want to achieve.

If you need the content to end up with a specific frame rate i.e. to put it on a Blu-ray, DVD or make it compatible to some streaming or hardware restrictions, then your goal is fixed. You should try to archive that goal while keeping as much of the original unique frames as possible.

Is there any scenario when the video should actually be processed at 29.97, aside from the occasional progressive DVD video?

If you aim to keep the original unique frames and the content is field-shifted and 29.97 fps, you should use field matching and stay at that frame rate.

Whether you:

1. keep the field/frames as they are
2. go "vfr", by removing duplicates and that's it
3. go for a specific frame rate

depends on your goal.
Usually you want to go for a specific frame rate and then you have to look at the content.
If the content has scenes with a lower frame rate, you can either get to that frame rate by adding more frames or speeding up the content. The later will require audio adjustments to stay in synch. When adding frames, you either add duplicates or you add interpolated frames. Personally, I prefer adding interpolations, when dealing with slow natural (= non-anime/cartoon) content like your baka sample, since for slow motion interpolation usually works fine without causing noticeable artifacts. (One often ends up with some duplicates remaining, around scene changes, but that usually is fine with me.)


=> It's all about the goal, there often is no 'right/correct/ideal/... way' to do something, things are often subjective and restricted by circumstances.
(that is basically true for most things in life )

Cu Selur

[hello_hello]

PAL stuff, or at least older PAL stuff, is generally converted to NTSC using field blending if it's shot on film, and using some type of interpolation to convert interlaced PAL to interlaced NTSC for video.... not always in great quality.

For the field blended PAL, you can usually convert it back to the original 25fps if you're an Avisynth user. For anything that was originally interlaced video, the best you can usually do is de-interlace it to 59.94fps with a high quality de-interlacer such as QTGMC.

There's no shortage of old BBC material that was shot on film for the outdoor shots and video for the studio shots. Old episodes of classic Doctor Who for example. After they're converted to NTSC you can de-interlace the video to 59.94fps and convert the film back to 25fps, but there's no way to do it automatically, it naturally becomes variable frame rate, and often involves a lot of work.

Progressive PAL can also be converted to 59.94i by slowing it down to 24.975fps and applying telecine (similar to NTSC telecine).

Are you sure the Crime Inc sample was originally PAL? I tried different methods convert it to 25fps but the smoothest output seemed to be deinterlacing to 29.97fps. It's hard to tell though because it seems to be old worn film with a lot of wobble and the camera pan isn't very smooth.

# Deinterlace to 59.94fps with QTGMC, hopefully for better quality.
QTGMC()
# Every second frame appears to be a duplicate, so delete them.
SelectEven()
# Cropping and resizing optional, of course.
CropResize(0,0, 14,4,-2,-2, ResizeWO=true, InSAR=10.0/11.0)