Why do people say 30F to 24F is hard conversion? at DVinfo.net

Roger Shealy · April 23rd, 2009, 07:09 PM

I shot a 30F (via 60i/.m2t) project using my XHA1 and loaded it into Vegas 8 Pro. I then rendered from the 30P timeline to 1080-24P and the footage looks great. I've heard 30 to 24 is almost impossible.

Perhaps I'm doing something illegal here, but the footage looks really good and it was extremely easy. What am I missing here?

Gene Gajewski · April 23rd, 2009, 08:52 PM

Not being an expert, I see the problem as one of temporal inaccuracy.

With 30p, you have frames created at an exact cadence of 33.3ms intervals. To get 24p you have to throw away 6 of them. Assuming you threw away every 5th frame, you wind up 24 frames but those frames are no longer from evenly spaced intervals. You'd get something like showing frames created at 33.3, 33.3, 33.3, 66.6....doled out at a 41.6ms rate to get 24 frames per second. Supposedly, some people can notice it.

Roger Shealy · April 24th, 2009, 05:41 AM

I was expecting to have a horrid stuttering piece with choppy audio given many comments on the subject. I'm just not seeing obvious flaws that many would notice. I'm looking pretty closely and I don't find anything offensive.

Douglas Spotted Eagle · April 24th, 2009, 06:16 PM

If you have much motion in the scene at all, you'll see ghosting artifacts. mathematically, there is no method from which to make this work cleanly. But it certainly can be done. Just not well.

Roger Shealy · April 24th, 2009, 08:41 PM

DSE,

The piece I'm looking at is low-motion (people walking, talking, sitting), so it isn't very demanding. Perhaps that's why I'm getting away with it. Looks great.

Roger Shealy · May 2nd, 2009, 06:31 PM

O.K., I had some footage with fast motion, and it looked terrible when converted from 30F to 24F. It's all clear to me now!

Thanks for the input.

Peter Moretti · May 4th, 2009, 05:56 PM

So do you have a frame rate recommendation if you want to deliver both 24P and 30P?

Would 60i be the best format to shoot in? I realize some vertical resolution would be lost in 24P, but it seems like 60i to 24P can be done pretty well. And I imagine 60i to 30P is straightforward.

Roger Shealy · May 4th, 2009, 06:29 PM

Never done 60I to 24, but that should work fine. I think Super will do that, as well as 30F.

David Jimerson · May 14th, 2009, 12:43 PM

If you have a project in which there is both 30p and 24p material (30F and 24F work out to the same thing in this regard), then your best bet by far is to edit and deliver as 60i. Not only is 30p (or F) to 24p (or F) often not a good conversion, the opposite is also true. It has to do with there not being enough of a difference between the number of time samples per second between the two; there's just not enough for a clean interpolation.

But both convert well to 60i (24p with 2:3 pulldown; 30p with 2:2 pulldown), so they'll live happily next to each other on that timeline. The only possible problem may be that people can tell the difference between the two -- but you can't do anything about that.

April 23rd, 2009, 07:09 PM	#1
Roger Shealy Major Player Join Date: May 2007 Location: Fayetteville, GA Posts: 772	Why do people say 30F to 24F is hard conversion? I shot a 30F (via 60i/.m2t) project using my XHA1 and loaded it into Vegas 8 Pro. I then rendered from the 30P timeline to 1080-24P and the footage looks great. I've heard 30 to 24 is almost impossible. Perhaps I'm doing something illegal here, but the footage looks really good and it was extremely easy. What am I missing here?

April 24th, 2009, 06:16 PM	#4
Douglas Spotted Eagle VASST Join Date: Jan 2004 Location: Stockton, UT Posts: 5,648	If you have much motion in the scene at all, you'll see ghosting artifacts. mathematically, there is no method from which to make this work cleanly. But it certainly can be done. Just not well. __________________ Douglas Spotted Eagle/Spot Author, producer, composer Certified Sony Vegas Trainer http://www.vasst.com

May 4th, 2009, 05:56 PM	#7
Peter Moretti Trustee Join Date: Mar 2007 Location: Sherman Oaks, CA Posts: 1,259	So is 60i the Answer? So do you have a frame rate recommendation if you want to deliver both 24P and 30P? Would 60i be the best format to shoot in? I realize some vertical resolution would be lost in 24P, but it seems like 60i to 24P can be done pretty well. And I imagine 60i to 30P is straightforward. __________________ Avid Media Composer 3.1.3. Boris Red and Continuum Complete. Vegas 8.0c. TMPGEnc Xpress Pro 4.0 Last edited by Peter Moretti; May 4th, 2009 at 09:56 PM.

May 14th, 2009, 12:43 PM	#9
David Jimerson Jubal 28 Join Date: Mar 2005 Location: Wilmington, NC Posts: 872	If you have a project in which there is both 30p and 24p material (30F and 24F work out to the same thing in this regard), then your best bet by far is to edit and deliver as 60i. Not only is 30p (or F) to 24p (or F) often not a good conversion, the opposite is also true. It has to do with there not being enough of a difference between the number of time samples per second between the two; there's just not enough for a clean interpolation. But both convert well to 60i (24p with 2:3 pulldown; 30p with 2:2 pulldown), so they'll live happily next to each other on that timeline. The only possible problem may be that people can tell the difference between the two -- but you can't do anything about that. __________________ www.wrightsvillebeachstudios.com

April 23rd, 2009, 08:52 PM	#2
Gene Gajewski Regular Crew Join Date: Sep 2007 Location: Edgewood, NM Posts: 162	Not being an expert, I see the problem as one of temporal inaccuracy. With 30p, you have frames created at an exact cadence of 33.3ms intervals. To get 24p you have to throw away 6 of them. Assuming you threw away every 5th frame, you wind up 24 frames but those frames are no longer from evenly spaced intervals. You'd get something like showing frames created at 33.3, 33.3, 33.3, 66.6....doled out at a 41.6ms rate to get 24 frames per second. Supposedly, some people can notice it.

April 24th, 2009, 05:41 AM	#3
Roger Shealy Major Player Join Date: May 2007 Location: Fayetteville, GA Posts: 772	I was expecting to have a horrid stuttering piece with choppy audio given many comments on the subject. I'm just not seeing obvious flaws that many would notice. I'm looking pretty closely and I don't find anything offensive.

April 24th, 2009, 08:41 PM	#5
Roger Shealy Major Player Join Date: May 2007 Location: Fayetteville, GA Posts: 772	DSE, The piece I'm looking at is low-motion (people walking, talking, sitting), so it isn't very demanding. Perhaps that's why I'm getting away with it. Looks great.

May 2nd, 2009, 06:31 PM	#6
Roger Shealy Major Player Join Date: May 2007 Location: Fayetteville, GA Posts: 772	O.K., I had some footage with fast motion, and it looked terrible when converted from 30F to 24F. It's all clear to me now! Thanks for the input.

May 4th, 2009, 06:29 PM	#8
Roger Shealy Major Player Join Date: May 2007 Location: Fayetteville, GA Posts: 772	Never done 60I to 24, but that should work fine. I think Super will do that, as well as 30F.