TMPGEnc NTSC/NTSC-film difference ?

[Anders_1982]

Hi
I'm encoding SVCD with TMPGEnc and I have a question.
In the version I'm using, 2.59.47.155, you can choose to encode
the SVCD as a NTSC or an NTSC-film file. But in NTSC you
can say that the movie is a film clip.
The NTSC-film runs at 23.976 fps if I'm not mistaking it.
And standard NTSC runs at 29.97 fps.
I've encoded a 23.976 fps avi into a NTSC-film mpeg2 and
a NTSC mpeg2 with the source to be a 23.976. I can't tell
any difference between the two. Both play at 29.97 fps in PowerDVD
and runs smooth without any signs of bad framerate conversion.
Does anybody know the difference and why there are two
alternatives that are that simular.

[adam]

You got the framerates correct.

Film is shot at 24fps. To get it to play on an NTSC tv it must be converted to 29.97fps at some time before it hits the tv. Now there is about a %20 difference between 24 and 29.97, and if you just sped it up then it would look ridiculous. So there is a process called a 3:2 telecine, whereby each field is split into two fields, this is called interlacing. Then fields are repeated in a 3:2 pattern. New frames are being created that did not exist before. So the fps is increased without actually speeding up playback, and since you are only duplicating very small bits of information at a time, the human eye does not notice it.

Now the problem with a 3:2 telecine is that it creates ~%20 new frames, and when you digitize these (encode to mpg for example) you now have the same amount of bits being spread out over many more frames. Essentially it is like lowering your bitrate by %20, which substantially degrades quality! As a solution, digital formats such as VCD, SVCD, and DVD, support what is called NTSCfilm. This lets you encode at 23.976fps, but have it play back at 29.97fps. The telecine process is done by the dvd player rather than the encoder, so you are still only encoding the original ~24 frames per second.

Since you had a 23.976fps source you should have used the NTSCfilm template. This would have maximized your bitrate. In using the NTSC template you wasted alot of bitrate, but since your source was arguably not that great to begin with, you might not have noticed the difference. Whether or not you see the difference that the %20 extra bitrate yields will depend completely on your source, your settings, your hardware, and your eyes. Always use ntscfilm if you can help it, it can significantly increase quality.