Relationship between Framerate and 3:2 Pulldown

[poerschr]

This post refers specifically to mpeg-2 creation with TMPGenc and AVIsynth.

One thing I do not quite understand....

What exactly is the relationship between framerate and 3:2 pulldown?

I have read many quides concluding that the best way to create mpeg-2 SVCDs is to use IVTC (decomb.dll in AVIsynth) (in my script file I use Telecide()) to convert the framerate to 23.976 fps. Then use as 3:2 pulldown so that the video plays back at 29.97 fps. This also makes the video progressive.

Most of all of the source material that I am working with is taken from DVDs that are interlaced.

If the orginal source material is film, running at 23.976 fps then you do not have to run an IVTC and you can encode the file at 23.976 and it will play that way on the DVD player?

Many guides recommed different encoding methods..It seems that you ideally want the source material in 23.976 fps...then two options 1) if the orginal material was film then no pulldown is needed 2) if the orginal material is 29.97 then the pulldown is needed...IVTC material provides less frames to encode, thus adding more data...improving quality...

Thanks....

[adam]

Not exactly. Simply put, if you encode at 23.976fps mpeg2 than you must include pulldown flags, everytime. The only time you would'nt use pulldown flags is if you encoded at 29.976fps, 25fps, or were using mpeg1.

The relationship between fps and pulldown flags is that the flags instruct the DVD player to telecine 23.976fps material to 29.97fps during playback. 29.97fps is the ONLY supported framerate in the NTSC standard, therefore 23.976fps material must always contain pulldown flags. The exception is mpeg1 which does not support pulldown flags, but which will be telecined automatically, though not as well.

In regards to NTSC DVDs, there are three things that can happen. For most DVDs they will be stored at 23.976fps already. So just use forced film in DVD2avi and encode at 23.976fps with pulldown flags. Some DVDs will be stored as NTSC (29.97fps interlaced) in which case you should IVTC, and once again encode at 23.976fps with pulldown flags. And finally a very small minority of DVDs will either be pure interlaced or so intermixed between film and NTSC that they will be impossible to IVTC. In these instances you should probably just encode it at 29.97fps interlaced which means that no pulldown flags are required.

[Gazorgan]

The key thing to remember is NTSC TV's can only display 29.97 fps.

So if you encode to 29.97 then you don't have to do anything.

If you encode to 23.97, you have to 'flag' the video so the player can create the extra frames to display it at 29.97 fps.

The advantage to encoding at 23.97 is less frames = more bits/frame = higher quality encode. Also, most DVD's are film and already 23.97 so that's one less thing to deal with.

[poerschr]

just the answer I was looking for...

Thank You for your help...