Why 30p? at DVinfo.net

Bryan Aycock · July 5th, 2006, 11:02 AM

Can someone please explain the difference between 30p and 60i footage--from how it is captured in the camera, to being recorded onto the tape, to being edited, to being output on DVD. I have an XL2 which shoots true progressive scan, so I'm assuming that the tape codec is the same for all formats, but that in 30p the XL2 just records one progressive image and then splits it across two fields on the tape?

David Jimerson · July 5th, 2006, 11:57 AM

The difference is that in 30p, you're taking 30 whole pictures per second.

In 60i, you're talking 60 half-pictures per second.

You may think that the 60i fields can be meshed together to make 30p frames, but that's not correct. Each 60i field is a separate moment in time, and if you put the fields together, any moving object will have interlaced artifacts around it, because you're actually looking at two moments in time, 1/60th of a second apart. Things can move awfully far in that span of time.

30p has whole pictures, 30 of them per second. That's half of the motion information of 60i. Becaues of it, moving objects are further apart between frames than they are between 60i fields, so the motion looks different, less smooth, a little bit more staccato.

As for capturing and editing, there shouldn't be any differences. 30p footage fits neatly onto a 60i timeline, and even though it's split into fields, field 1 and field 2 from each frame is the same moment in time, so the motion cadence is the same, and because the camera didn't need to do any anti-flicker correction while recording, as it must in 60i, the picture retains its progressive aesthetic.

As for why to use it, well, that's an artistic choice.

Bryan Aycock · July 5th, 2006, 04:21 PM

I'm producing a hunting video, and was thinking of shooting the actual hunting footage in 60i, because of the unpredictability of the subject being filmed, and all of the interview segments in 30p. So if I've been editing 60i footage on my timeline, I should see no difference? And I should treat it the same when I'm burning a DVD? Will it play okay on a CRT television? Thanks.

Bennis Hahn · July 5th, 2006, 06:08 PM

You will see a difference because of the nature of progressive. Next to 60i, it will look a tad stuttery. I personally find this effect flattering so it is not necessarily a bad thing. Just put for 30p on the 60i time line and render as a 60i file and everything should be fine. You will retain the aesthetics of 30p.

David Jimerson · July 5th, 2006, 07:56 PM

To clarify:

30p will continue to look like 30p in a 60i stream.

When capturing, editing, and exporting 30p, your workflow should be the same as editing 60i. You can also edit in a 30p environment, but you don't have to.

Bryan Aycock · July 7th, 2006, 12:04 PM

What are the advantages of editing 30p on a 30p timeline, rather than 30p on a 60i timeline?

David Jimerson · July 8th, 2006, 07:52 PM

Effects (transitions, text, compositing, etc.) would be treated as 30p and not 60i. They'd look a bit less video-like.

Bryan Aycock · July 16th, 2006, 05:20 PM

David (or anyone):
How does editing in a 30p timeline work better with effects and transitions. I'm assumming that if I were to have some text fly in, that it would fly in at 30p, not 60i? Okay, so say I'm working on an After Effects project for my 30p timeline in FCP--I would have to export this AE sequence as a 30p sequence for the 30p timeline it's going in? Am I wrong in assuming this?

David Jimerson · July 16th, 2006, 05:28 PM

Remember that video is essentially a whole bunch of still pictures shown in a rapid sequence, with each picture being a little different than the last. Something moving from left to right will be a little bit further to the right in every picture.

Imagine each picture is a stop. 30p has 30 stops. 60i has 60 stops. 60i appears smoother because there's less difference between the stops, less distance for the object to travel, so there's less of a jerk when the move is made.

If you edit in a 60i field, your motion graphics, etc., will appear to move a little bit more smoothly than your video. Now, this isn't as big a deal as it would be if you were editing 24p in 60i (the difference in motion would be stark), but you may notice the difference.

If you edit in 30p, your effects should take on a 30p motion cadence, matching the video.

Bryan Aycock · July 16th, 2006, 06:29 PM

Thanks, but I'm just having trouble understanding how FCP would recognize a 30p sequence. What if I'm working on some motion graphics in After Effects; is there an option to export this in a 30p format for my 30p timeline?

David Jimerson · July 16th, 2006, 06:34 PM

Quote:

Originally Posted by Bryan Aycock

Thanks, but I'm just having trouble understanding how FCP would recognize a 30p sequence. What if I'm working on some motion graphics in After Effects; is there an option to export this in a 30p format for my 30p timeline?

I haven't used AE for quite some time, but if I recall correctly, you can export as 29.97 progressive (or "non-interlaced," as AE might call it).

Matt Vanecek · July 17th, 2006, 09:38 PM

Quote:

Originally Posted by David Jimerson

I haven't used AE for quite some time, but if I recall correctly, you can export as 29.97 progressive (or "non-interlaced," as AE might call it).

In AE you right-click the clip in the list of assets and do an "Interpret Footage", changing the field interpretation to off (I forget the name of the combo box on the dialog--I just kindof do it by feel nowadays...). When exporting the footage, make sure the lower/upper/none field option (I think it's "Field Order") is set to none (or is it "off"?), and don't deinterlace (deinterlacing progressive stuff looks kinda bad). You really want to work with the 30P as 30P for as long as possible, up to your final export, in my opinion.

Wow, I really do kinda zone through that stuff--I cannot remember a single AE field name, but I got them all pictured perfectly (w/o labels of course!!) in my head....

HTH,
Matt

July 5th, 2006, 11:02 AM	#1
Bryan Aycock Regular Crew Join Date: Apr 2006 Location: Hammond, LA Posts: 84	Why 30p? Can someone please explain the difference between 30p and 60i footage--from how it is captured in the camera, to being recorded onto the tape, to being edited, to being output on DVD. I have an XL2 which shoots true progressive scan, so I'm assuming that the tape codec is the same for all formats, but that in 30p the XL2 just records one progressive image and then splits it across two fields on the tape?

July 5th, 2006, 11:57 AM	#2
David Jimerson Jubal 28 Join Date: Mar 2005 Location: Wilmington, NC Posts: 872	The difference is that in 30p, you're taking 30 whole pictures per second. In 60i, you're talking 60 half-pictures per second. You may think that the 60i fields can be meshed together to make 30p frames, but that's not correct. Each 60i field is a separate moment in time, and if you put the fields together, any moving object will have interlaced artifacts around it, because you're actually looking at two moments in time, 1/60th of a second apart. Things can move awfully far in that span of time. 30p has whole pictures, 30 of them per second. That's half of the motion information of 60i. Becaues of it, moving objects are further apart between frames than they are between 60i fields, so the motion looks different, less smooth, a little bit more staccato. As for capturing and editing, there shouldn't be any differences. 30p footage fits neatly onto a 60i timeline, and even though it's split into fields, field 1 and field 2 from each frame is the same moment in time, so the motion cadence is the same, and because the camera didn't need to do any anti-flicker correction while recording, as it must in 60i, the picture retains its progressive aesthetic. As for why to use it, well, that's an artistic choice. __________________ www.wrightsvillebeachstudios.com

July 5th, 2006, 04:21 PM	#3
Bryan Aycock Regular Crew Join Date: Apr 2006 Location: Hammond, LA Posts: 84	30p I'm producing a hunting video, and was thinking of shooting the actual hunting footage in 60i, because of the unpredictability of the subject being filmed, and all of the interview segments in 30p. So if I've been editing 60i footage on my timeline, I should see no difference? And I should treat it the same when I'm burning a DVD? Will it play okay on a CRT television? Thanks.

July 5th, 2006, 07:56 PM	#5
David Jimerson Jubal 28 Join Date: Mar 2005 Location: Wilmington, NC Posts: 872	To clarify: 30p will continue to look like 30p in a 60i stream. When capturing, editing, and exporting 30p, your workflow should be the same as editing 60i. You can also edit in a 30p environment, but you don't have to. __________________ www.wrightsvillebeachstudios.com

July 7th, 2006, 12:04 PM	#6
Bryan Aycock Regular Crew Join Date: Apr 2006 Location: Hammond, LA Posts: 84	Editing 30p What are the advantages of editing 30p on a 30p timeline, rather than 30p on a 60i timeline?

July 5th, 2006, 06:08 PM	#4
Bennis Hahn Major Player Join Date: Mar 2005 Location: Richmond, VA Posts: 221	You will see a difference because of the nature of progressive. Next to 60i, it will look a tad stuttery. I personally find this effect flattering so it is not necessarily a bad thing. Just put for 30p on the 60i time line and render as a 60i file and everything should be fine. You will retain the aesthetics of 30p.

July 8th, 2006, 07:52 PM	#7
David Jimerson Jubal 28 Join Date: Mar 2005 Location: Wilmington, NC Posts: 872	Effects (transitions, text, compositing, etc.) would be treated as 30p and not 60i. They'd look a bit less video-like. __________________ www.wrightsvillebeachstudios.com

July 16th, 2006, 05:20 PM	#8
Bryan Aycock Regular Crew Join Date: Apr 2006 Location: Hammond, LA Posts: 84	Effects David (or anyone): How does editing in a 30p timeline work better with effects and transitions. I'm assumming that if I were to have some text fly in, that it would fly in at 30p, not 60i? Okay, so say I'm working on an After Effects project for my 30p timeline in FCP--I would have to export this AE sequence as a 30p sequence for the 30p timeline it's going in? Am I wrong in assuming this?

July 16th, 2006, 05:28 PM	#9
David Jimerson Jubal 28 Join Date: Mar 2005 Location: Wilmington, NC Posts: 872	Remember that video is essentially a whole bunch of still pictures shown in a rapid sequence, with each picture being a little different than the last. Something moving from left to right will be a little bit further to the right in every picture. Imagine each picture is a stop. 30p has 30 stops. 60i has 60 stops. 60i appears smoother because there's less difference between the stops, less distance for the object to travel, so there's less of a jerk when the move is made. If you edit in a 60i field, your motion graphics, etc., will appear to move a little bit more smoothly than your video. Now, this isn't as big a deal as it would be if you were editing 24p in 60i (the difference in motion would be stark), but you may notice the difference. If you edit in 30p, your effects should take on a 30p motion cadence, matching the video. __________________ www.wrightsvillebeachstudios.com

July 16th, 2006, 06:29 PM	#10
Bryan Aycock Regular Crew Join Date: Apr 2006 Location: Hammond, LA Posts: 84	30p Thanks, but I'm just having trouble understanding how FCP would recognize a 30p sequence. What if I'm working on some motion graphics in After Effects; is there an option to export this in a 30p format for my 30p timeline?