telecine question

[tommcd64]

I am using tmpegenc to encode an avi. The frame rate of the avi is 23.976. I know that this needs to change for my ntsc mpeg file to work in my system. My question is this, do I need to check the inverse telecine in the advanced tab or should I just select 3:2 pulldown when playback in the encode section under the video tab?

[Vejita-sama]

The you want to select 2:3 pulldown, note the easiest way to do this is to load one of TMPGenc's 'film' templates (this has the pulldown flagged check and the resolution preset).

Do a search (here and at doom9.org but might want to try google) on interlacing, de-interlacing and IVTC. But here's an outline.

When TV was invented it was not possible to have a frame rate high enough to support 'seamless' motion. Long story short it was possible to send each frame as two fields. Each field has 1/2 the lines. One field has all the odd lines, and the other field has all the even lines. Two fields make one frame. So TV is actually 60 frames per second. This process is known as interlaced.

Movies (and all computer/digital video) on the other had is progressive. That is each frame is a complete 'screen shot' (ie. no fields). Films are also shot at 23.976fps.

Now you TV will ONLY display interlaced 29.97fps video. So the question is how do you get a film to play on a TV. You convert it from 23.976fps/progressive to 29.97fps/interlaced. This process is known as teleciding.

Most DVD players can actually do this on the fly, the 2:3 pulldown flag tells you're DVD player to do so.

Now let's say I want to encode a ripped DVD/DivX file. That's a film source telecided to 29.97fps. I could just encode it, but I'd get better results if I first convert it back to 23.976fps/progressive. This process is known as inverse teleciding (aka ICTV).

Why would be want to do this. Well it increases the bitrate per frame. Compare:

1800kbit/s video @ 29.97fps = 60.1 kbits/frame
1800kbit/s video @ 23.976fps = 75.1 kbits/frame

In this case that's a 12% 'effective increase in bitrate' for the same size file. NOTE - the file size is unchanged. File size is set by the bitrate and the runtime (eg. 1800kbit/s * 3600 secs). The resolution, frame rate, etc. doesn't matter.

Hope that helps. Check doom9 for more info:

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

[tommcd64]

Thanks for the info. That really helped a lot. I was wondering if you might be able to answer another question I have trying to find. I know what the basic difference is between the 2:3 pulldown and the 3:2 pulldown. When would you want to use the 2:3 versus the 3:2? I convert most of my avi's using mainconcept encoder unless they have a funky size and the tmpegenc is better suited for that. When using the main encoder, I used the 3:2 pulldown and everything looked okay. You recommended using the 2:3 pulldown. I was just wondering what the difference was as far as viewing the movie and what would be a rule of thumb as when to use 2:3 and when to use 3:2 pulldowns? Sorry about all of the questions. I do appreciate any info you can give me.

[adam]

tommcd64 its basically the same thing. I think technically the conversion is referred to as a 2:3 telecine, but I've seen the pulldown flag referred to as 2:3 and 3:2. Either way it just means that the fields are repeated in a 2:3 pattern.

If you use TMPGenc it calls it 3:2 pulldown, if you use pulldown.exe it calls it 2:3 pulldown. Note that in TMPGenc the 3:2 pulldown flag is located on the VIDEO tab, NOT the ADVANCED tab. The one on the advanced tab is a filter which will do a hard telecine which you don't want. This means you will phyiscally do the conversion to 29.97fps rather than let your dvd player do it. This lowers the quality by quite a bit. But as Vejita-sama noted, simply loading the ntscfilm templates take care of all this for you.

[BJ_M]

couple of small errors there Vejita-sama:

When TV was invented it was not possible to have a frame rate high enough ................

that wasn't the reason exactly.

Movies (and all computer/digital video) on the other had is progressive. That is each frame is a complete 'screen shot' (ie. no fields). Films are also shot at 23.976fps.

digital video can be progressive or interlaced, most is interlaced. Film most often is shot at 24fps , but 30fps , 48fps and 60fps is also used.

The resolution, frame rate, etc. doesn't matter

the resolution will mater on file size ..