20 May
2008
20 May
'08
10:49 p.m.
Florin Andrei wrote:
NTSC DVD is 720x480, aspect ratio either 4:3 or 16:9 (non-square
pixels), at 29.97 frames per second interlaced (so it's 59.94 fields per
second).
If it's progressive (non-interlaced) then the frame rate is 23.97 fps
with 2:3 pulldown.
This whole frame rate and interlacing issue is not trivial. Make sure
you process the video stream the right way before encoding, otherwise
you end up with a russian roulette candidate.
I did pretty much all my movies entirely in the standard 30i format
(29.97 interlaced) - the entire processing chain, start to end, was 30i.
I don't have much experience with 24p (23.97 progressive). But it's a
popular, well known and well understood format, so it should work -
provided that the tools are standards-compliant.
Speaking of that:
If the source is progressive (non-interlaced) I would attempt first to
convert it to 24p (23.97 progressive) with 2:3 pulldown, and make a DVD
using that format and see if it looks good. The idea is to keep
everything progressive all the way from the source to the DVD, and just
do frame rate conversions instead of also messing with the nature of the
frames (interlaced or progressive).
I could be mistaken, but I don't quite like the idea of converting
progressive frames to interlaced. It will look rather unnatural anyway
(like a bad film-to-DVD transfer) even on an interlaced display (such as
a regular standard definition interlaced TV with a CRT tube), but if you
show it on a progressive display (a computer, or a plasma/LCD/DLP TV)
then there will be so many progressive / interlaced / progressive
conversions that my guess is it will totally screw up the image.
I never tried to do that, so I don't know for sure. But you probably
know where I'm getting at - the fewer conversions, the better.
Only if that totally fails and it looks ugly, you should consider
converting your progressive source to 30i (29.97 interlaced) DVD.
You may also try to generate 30p (29.97 progressive) MPEG2 from a
progressive source of arbitrary frame rate, but make sure all the tools
involved after that (the multiplexer, the DVD authoring tool) support it
100%. I'm not even sure whether 30p is "legal" for an NTSC DVD. If it
is, it might be the better option for arbitrary frame rate progressive
sources, since there's no 2:3 pulldown involved.
The DVi forum is a good place to ask subtle questions like that. Here's
a thread on a related topic:
http://dvinfo.net/conf/showthread.php?t=77998
--
Florin Andrei
http://florin.myip.org/