delivery format/frame rate question
 

trying to figure something out with regard to film in the digital arena.
my background is film and i have a lot of film archived both on film as
well as videotape. if i digitize these materials as 24 frame sequences,
for example scanning the film frames to individual files, can i create
files (like avi or qt) that play at 24fps? what is the delivery medium
for such a file for digital projection? is there a 24fps mp2 file for dvd?
do digital projectors run at 24fps? if so, what is the media they use?

sorry to be obtuse but haven't found anything that answers such
basic questions in my searches.

Hi George,

If you shoot and edit in 24fps, every encoder I know of can encode in 24fps including QuickTime and Windows Media. Many people encode their DVDs at 24fps because it's more space effecient too compared to NTSC 29.97.

so it's not actually folded into a 30fps file and flagged?

If it's FILM it's 24fps (not always though . . . I've worked on tv spots shot on 35mm film at 30fps for example to avoid 3:2 pull down for xfer to video). Video shot at "24fps" might actually be 23.98 for example. If it's shot with Panasonic DVX100, it's recorded to tape at 29.97 with "3:2 pulldown" fields/frames added. Panasonic also gives you the choices of 2 cadences "24p" and "24pa." It's on tape at 29.97 fps (NTSC) though. A good NLE like Final Cut Pro can remove the pulldown fields/frames on import so you can work on a 24fps time line (sequence). Tools like Cinema Tools can do that too.

With "24fps" you need to know what the source was and think alot about your workflow and target.

Actually your question is very good and more people in post production should be asking it. So many projects can become a real mess when people don't understand the different ways 24fps can be handled depending on the source, workflow, end product.

so i gather from the reference to space saving that the final file
can, in fact, have only 24 frames per second of projection time.

here's my reason for asking. i have quite a bit of material on
video that was shot on film long ago. i no longer have access to
the film original as it has deteriorated. the video tape, however,
is fine. i thought i might preserve it as best as i could by sending
it to a digital format at the original frame rate. i thought i'd do
this by:

1. digitize the videotape
2. deinterlace
3. export as sequence of numbered still frames (30fps)

the deinterlacing results in a duplicate frame every five frames.
i wrote a bash script for my linux box to discard the duplicate
frames and renumber the remaining ones so there'd be no gaps
in the sequence numbering.

4. re-import numbered stills (24fps)
5. encode to delivery format

my question is, is the re-encoding for a delivery format just
going to re-wrap the laboriously worked frames into a 30fps
file as 24p does. btw, took me a long time to find the interlace
pattern for 24p and 24pa. everybody stops with the frame
cadence but doesn't tell the interlace pattern. anyway,
from what i've gathered so far, it should be possible to do
steps 5 and 6 in a true 24fps environment rather than folding
the 24 frames into 30. am i correct in this? mpeg-2 can encode
directly to 24fps?

thanks

An MPEG 2 encoder should encode to true 24fps, otherwise there'd be no space saving.

As you note the "cadence" also includes interlacing but there's an important caveat in the direction you're heading with the script you've written.

If you're dealing with straight flim to video xfers, things should be constant.

If you're dealing with film that was edited to video, the edit points can change that cadence if it was edited on video (unless it was done on a 24fps time line with the pull down removed).

Don't forget MPEG2 as well as other "compression" codecs are just that. They are not lossless.

If you're dealing with masters and you want to stay as pristine as possible and have the budget, maybe you should xfer the material to HDCAM.

Then compress HDCAM new masters to whatever the flavor of the day is. You might do MPEG2 this year but 2 years from now you might get better results with codecs designed for HDDVD/BluRay when it comes time to distribute that way.

thanks craig.

this leads me to think what i'm doing is a viable solution. all tapes are
straight xfers with no editing. as for archiving, i thought i'd save the
exported stills directories as the masters. save any re-xfer costs and
probably the most versatile way to go. also, as i said before, much of
the material is no longer available in its film form. as stills, i should be
able to manipulate them in fairly high end imaging software to
interpolate frames up or down in resolution to match the flavor of
the month delivery format, and probably do a better job than my
video apps would.

bottom line of my thinking is that the most versatile archival format
is probably not a video format but one of stills.

thanks again,
george

ideally stills compressed in a lossless format (or not compressed at all). Of course make sure your frames are very high resolution for long term future use. Today's high resolution still might be tomorrows low resolution (if you wait enough years).