Frame rate conversion and reverse pulldown.

Posted by john 
Frame rate conversion and reverse pulldown.
October 13, 2011 09:12PM
Hi all,

I have some old 8mm film footage that was scanned at SD 4:2:2. The original footage was 18 fps (I believe). When I received the footage it plays at 29.97 fps (speeding up the footage dramatically). This footage will play in a sequence that is 29.97 fps. Does anyone know of an easy way to convert the footage so that the quality of the original is preserved (a formula that duplicates certain frames as is done for 24p footage in a 30p sequence)?

I know there are post houses with expensive equipment to do this but if there's a homegrown solution I'd love to know it. Right now the workaround I'm considering is to export the footage from fcp as an 18fps file then try to conform it to 29.97fps.

Help please



Re: Frame rate conversion and reverse pulldown.
October 14, 2011 04:08AM
i've got a pretty simple way of figuring this sort of thing out in FCP.

you've got 18 frames that you need to play for 1 second?
so add 18 frames of slug to the timeline, select it, open the modify speed window,
and change the duration to 1.00.

that'll give you the percentage you need to apply to the other clips/s


not all 8mm is alike.

Super-8 runs at 18fps (sometimes 24fps)

Standard 8 is 16fps

a very simple 50% slow-down of 16fps material will give you something close to normal speed ina 29.97 timeline without too much artefacting.

Re: Frame rate conversion and reverse pulldown.
October 16, 2011 10:52PM
thanks Nick,

Do you know how the software slows down / speeds up the speed (frame interpolation or duplicating certain frames)?

Re: Frame rate conversion and reverse pulldown.
October 17, 2011 12:21AM
Oops I just realized that there is a sort of "pull-down" (is that the right word) of 1 duplicate frame after 1 original frame and then another duplicate frame after 2 more original frames. I guess that's what keeps every thing at 30 fps? I would like to remove the pulldown for use in a speed adjusted sequence and I'm wondering if you can recommend software to do this. I've tried Cinema Tools but it only converts 24 and 30 fps (as far as I can tell). Any ideas?
Re: Frame rate conversion and reverse pulldown.
October 17, 2011 04:36AM
im a bit confused.

in your first post you said the 18fps was telecined at 29.97
so you should have one film frame per video frame.

is the effect you describe AFTER you've modified the speed?

you can opt to have the frames blended in the modify speed window.
it's not great.

you can try sending to motion and using optical flow, but it's not that good with complex footage (and old 8mm can be complex), and it can take a very long time.

Re: Frame rate conversion and reverse pulldown.
October 17, 2011 07:03AM
I tried a reverse pulldown for 8mm before and could never get it to work - the pattern wasn't constant or stable and we got into all manner of bother trying.

Re: Frame rate conversion and reverse pulldown.
October 18, 2011 12:17AM
the repeat pattern for 18 to 24 would be 1,2,3,3

18 to 30 boils down to 3 into 5, so the pattern described above makes sense: 1,1,2,3,3

i dont know why, but FCP doesn't handle speed changes at the field level.
so while a simple 50% speed on interlaced materiel should give you a good slow-mo with each field re-mapped to a frame, FCP doesnt do that, so you need to use another Nattress filter to make it work.

Re: Frame rate conversion and reverse pulldown.
October 18, 2011 11:24AM
Ok final question,

I went into cinema tools and did a "reverse telecine" which gives me a frame sequence of 1,2,3,4,4, So all I need to know now is if there is a "cut automation" function in FCP 7. (i.e. can I ask FCP to cut out ever 5th frame)? I don't believe the Natress filters will work based on Graeme's kind response above.

thanks guys.
Re: Frame rate conversion and reverse pulldown.
October 19, 2011 06:19PM
you could try a speed up to 120% ( i think that would be the correct setting) and turn off frame blending.
a lot would depend on your starting frame, and also, i fear it wight not hold for a long period,
or even work.
i am finding it near impossible to get FCP to give be a clean, round-figure speed setting these days.

i do have a manual method for doing what you want.
sorry to tease, but i have to go right now!
i'll write it up in an hour or so.

Re: Frame rate conversion and reverse pulldown.
October 19, 2011 07:21PM
ok, here's what you can do>

this method is based on working in a timeline, removing the frames, and exporting the results,
so first put your clip/s into a new timeline.

on a track above your clip, lay down 4 frames of slug, followed by 1 frame of text.
line them up so the 1 frame of text is placed over your 5th duplicate frame.

copy those 5 frames, paste them 11 times.
now copy those 60 frames, copy them 4 times
copy that 10 seconds of frames, and copy 5 times
copy that minute of frames and copy as much as you need.
(or something along those lines)

now do a timeline search for "slug", find all, and delete.
now either do a search for all "text", or just use the track tool to select all the single frame text clips,
hold shift, drag them down, his will slice out your unwanted frames,
while they are still selected, hit delete.

you should now have a pattern of 4 unique frames followed by a 1 frame gap where the duplicate was.
place you playhead at the head of the sequence, select all in the timeline,
and drag everything up into the canvas and drop it into the overwrite window.
that will remove all the gaps.

you'll have some excess media at the end of the gapless section so tidy that up, and export.

of course once you do all this, i think you might be back where you started, with every film frame mapped to one video frame, and the footage playing fast.

Re: Frame rate conversion and reverse pulldown.
October 22, 2011 04:15AM
Thanks Nick - fantastic work-around smiling smiley
Sorry, only registered users may post in this forum.

Click here to login



Web Hosting by HermosawaveHermosawave Internet

Recycle computers and electronics