3:2 Pulldown

[EnNiS]

I have read about this (3:2 Pulldown in tmpgenc)
and i was wondering what the hell is it??
what does it do and whats it's purpose??
i have a Ntsc video and an NTSCfilm and a couple Pals, when should i use it etc.
and why would i use it?

thanx

[Vejita-sama]

Here's the short (no really) verison. First you only need worry about pulldown with NTSC (US, Canada and Japan) source. PAL (most of europe) doesn't have this problem.

When TV was first invented it was not possible to have a produce/broadcast a high enough framerate to create seamless motion. So someone came up with the idea of spilting each frame into two fields. Each field would have 1/2 the lines of each frame. One field has all the even lines, and the other all the odd lines. TVs then get 60 fields per sec (ie. 30fps). This works because each field stays on the screen after it's been sent. To the human eye it all looks seamless. This process is known as interlacing.

On the other hand movies are shot at 23.976fps (24fps) progressive. Progressive in that each frame is a complete still image from the movie. The problem is that your TV is set up to ONLY show 30fps interlaced video. So to play films on your TV we need to convert the 24fps/progressive source -> 30fps/interlaced video.

This is done by a process known as teleciding (aka pulldown). For more info check out:

http://www.doom9.org/synch.htm

basically what you do is take four frames of film (ABCD) spilt them into fields, then make new frames:

Frames -> fields -> new frames
ABCD -> AABBCCDD -> AA AB BC CC DD

By this process you find that each 2 new frames are made of 'hybrid' info, and 3 are made from the original source. Hence, 2:3 pulldown (it's actually 2:3 pulldown not 3:2, but that's a who other debate).

So if you have a 24fps/progressive source and want to encode it. You pulldown/telecine. For a 30fps/interlace source you do nothing (unless you're making a VCD).

Now here's where people get confused. If you have a 30fps telecided source (eg. DVD rip) and you want to encode it. You'll get a better result if you first convert it back to 24fps/progressive. This process is known as inverse teleciding (aka IVTC).

So why would we want to do this. Because it produces better encodes. For example:

1850kbit/s video at 30fps = 61.7kbit/frame
1850kbit/s video at 24fps = 77.1kbit/frame

that's a 25% effective increase in bitrate for the same size file!

So now you're thinking great, I should run IVTC on everything. But that would be a mistake. Because you are chaning the framerate. And you can't just do that (hence all the PAL <-> NTSC treads). That's why all those old time baseball clips have everyone moving in fast forward.

Only run IVTC on 30fps/telecided source.

Ok that really was the short verison. Hope this helps. Any other questions?

[EnNiS]

yeh thats great thanx
but i have encoded tons of 23.976 using th entscfilm template without using the pulldown
....

[Vejita-sama]

The NTSC_Film templates add the pulldown flag. That's why there are film and 'std' templates. Pulldown or no pulldown.

[EnNiS]

OOOOOH ok thanx a shit load buddy i help me a lot
now i just gotta fix this prob
i got these two xvids.
the have vbr so i had to do the conversion shit in vdub and i frameserved it to tmpg, and thers no audio, and heres the fucked up part. it crashed on me with 16 minutes left in it so i sourceranged it from the fram it left off of and starting from where i left off (on the new mpg file) it has AUDIO!! but its not in synch at all, its from an enitrely diff part of the movie.
weird huh
wwel thanx
cya