Opinions on Converting 30P to 24P ProRes

Hello Everyone,

I'd like some opinions on potential workflow issues. I'm going to be producing a short on the new Canon 5d Mark II. Obviously, this camera only shoots 30P (actual 30P not 29.97). It records in an H.264 format at around 40mbits/s. The first thing to be done with the footage is to convert to ProRes422 via Compressor. This is where I thought it would be good to immediately convert to 24p before beginning to edit.

How do you recommend going about this? Potential output is going to be DVD and broadcast (SD) television for sure. I'd also like to preserve the ability for Blu-Ray and possibly even film out.

I've messed around quite a bit with compressor, not really knowing what I'm doing. I've got some footage from the 5D MII I've been testing (haven't gotten my camera yet).

Making a duplicate of the Apple Pro Res 422 pre-set and then changing the frame rate in video settings to 24fps and then turning on frame controls and setting the de-interlace setting to "Reverse Telecine" seems to give decent results. That creates a ProRes video in 24fps and not 23.98 though. Plus, I think technically speaking, that's the completely wrong process.

I'm concerned about all kinds of things here, chief of which are overly jittery video (but maintaining the 24p cadence) and sound synchronization. Audio for the short will be recorded separately to a Sound Devices 702. Obviously we won't be working with any sort of time-code at all.

Help me here, I know I'm messing something up! Thanks!

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I'm going to be producing a short on the new Canon 5d Mark II.

Run. No, seriously. Run. While I haven't had hands-on with a Mark II myself, everything I've heard about it is that it's nigh-on useless for production. For example, according to an acquaintance of mine who shot with it, the camera doesn't preserve exposure settings between takes. Every time you want to roll on a take, you have to shine a flashlight down the lens to get it to stop down, or what have you.

If you have any choice in the matter at all, get out while you can.

Or charge a bloomin' fortune to cover your time and frustration.

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This is where I thought it would be good to immediately convert to 24p before beginning to edit.

Unfortunately converting from 30p to 23.976p is impossible to do perfectly, and very hard to do well. It's not a trivial matter, like shuffling fields to go from 24 to 60. You have to interpolate between frames, which introduces an unavoidable softness in the image, like it's ever so slightly out of focus. If you're shooting 1080 and stepping down to SD, that'd probably be acceptable, but if you're planning to go out 1080, definitely do some tests first to make sure you don't hate the result.

Compressor's frame-controls tab does provide some great options for doing high-quality interpolation for things like frame-rate conversion or scaling. The trade-off is time. Again, do some tests on your equipment to see how many minutes of processing time it'll take per second of raw footage. Generally Compressor offers "good," "better" and "best" settings; convert a couple seconds with each setting, and see what you get. It's handy to take the results into Final Cut and compare them by stacking them on your timeline in pairs, setting the V2 clip to "difference." This pulls a difference matte, and will highlight only the parts of your footage that differ between the clip on V1 and the one on V2. That'll make it easier for you to decide whether this one looks a lot different from that one, or just a little different.

Running a reverse-telecine on this footage won't give you any meaningful results, as the source material is not interlaced in the first place, and certainly has no 3:2 in it.

Something else to beware of is the shutter. If I remember correctly, the Mark II gives you two shutter options when it's shooting video: 1/125 (which is just ludicrous) and 1/60. Neither of these is 1/48, which is the correct shutter speed to use when shooting 24p material. Shooting with a 180° shutter gives you the motion blur characteristics most commonly seen in movies, so it looks "right." If you shoot with an off-speed shutter, which people sometimes do for artistic reasons, then it looks "wrong" in a way that can be hard to explain. This is another reason why you really should do some tests with frame-rate conversion before you commit; even if Compressor gives you results that don't look too soft, you might hate the "wrongness" of the quality of motion, due to the shutter speed.

The happy medium, of course, is simply to conform the 30p material to 29.97p, using Cinema Tools. That leaves the data in the file alone, but changes the speed at which it plays back. That way you can just cut it in a timeline with a 29.97 timebase. You'll have to conform your audio as well, before synching your rushes, but that's straightforward.

I don't mean to be Mr. Negative here, but seriously, based on everything I've heard so far, you're in for a very difficult time. The new Canon and Nikon DSLRs-oh-by-the-way-with-video-too-kind-of are, in my totally worthless opinion, just not useful for film production. Not even for short-film production. You're better off using an HV30.

Either way, please let us all know how it goes.

I've got an obvious bias here, being that my preferred solution to getting a very nice 24p involves at $17,500 purchase on a primary coloured camera.

Putting that to one side, I don't know of a good way to convert 30p to 24p that will make it look good. I'm not saying it can't be done, but that I've not seen it done well. That, and the big issue Jeff points out that the shutter speed is "wrong" for filmic motion at 24p - and as that's sorta burned into the picture, there's very little you can do about it. The desired film look is as much that particular shutter look as it is the 24p.

Then there's the "dance" you do every time to get the camera to be the desired exposure.

Quite frankly, although the test footage from the 5D2 shows lovely DOF, and what having nice glass can do to an image, it also shows harsh compression artifacts (think what we don't like about HDV) and some quite nasty aliasing - [s3.amazonaws.com] is a good example of that, on the train, and the shutters.

I'd personally, if I didn't have that primary coloured camera, I'd be shooting a Panasonic P2 camera in 24p.

Graeme

Thanks for the tips, Jeff. Yes, I have a feeling the 5D MII is going to present challenges. However, you can gain more control over exposure by using manual Nikon or Zeiss lenses with an adapter. This gives you full control over f-stop. Yes, the camera can shoot at 1/125, but it also goes down to 1/30. So, unlike most cases, the lower light the better. Will need ND's for outdoors.

I tried a new method. I converted the 5D footage to ProRes HQ using same settings. So the ProRes file is 1920X1080 at 30p. I took that into Cinema Tools and conformed it to 24p. I dropped that into FCP and surprisingly, it really doesn't look to bad (it may even be passable). Obviously it changed the pitch of the audio included with the clip. Like I mentioned though, I'm recording audio separately to a Sound Devices 702. Is there a conform I would need to do there or does one second of audio correspond with one second of video regardless of frame rate (I'm not familiar with this at all, having never done it)? Plus, should I try to be conforming to 24p or 23.98p? I'm not familiar with 23.976p.

I don't know... maybe I should just stick with 30p! I just wanted a more filmic look with the depth of field control that I'll be afforded.

Simply put, I think the 5D MII could have been AWESOME but for some reason Canon has chosen to cripple it with no 24p or manual exposure control. At this point, with my shoot not until the first week of May, I'm praying for a really nice firmware update!

Graeme, yeah, if I had $17,500 (actually you need more like $28,000) I'd go with that option too. Then I'd own the camera and shoot whatever I wanted, albeit with much more needed light! If I had more TIME I'd go with it's new lighter priced cousin (or is it a step brother?). But, alas...

Well, remember some of that extra light - who knows how much really, is because the 5D2 is shooting at a 360 shutter, rather than the 180 degree shutter that the more filmic users will shoot at - there's a whole stop there. There could be more, but without one at hand to analyze, I don't know what they're doing with the tonal curve etc.

Yup, pricey I know for a RED, but still, for the quality of image.... Not much I can do about the price other than work hard to make Scarlet as good as it can be. (Can you imagine Jim making Scarlet only do 30p to "protect" sales of Epic and Red One??)

The "NTSC" rate for 24p is 24 * 1000/1001, which is 23.97602397602 which is a mouth full. So it's rounded to 23.976 for 23.98 or 24p. They all mean the same, just different ways to say it. 30p usually means 30 x 1000/1001 fps, but in the case of the 5D2 it's 30.00fps - ie exactly 30fps, rather than the NTSC standard rate. So you need to ensure that the external audio knows that, or syncing is going to be a pain. It's going to be tricky anyway.

Conforming the 30.00fps to 24p basically slows the video and audio down. That's fine for stock footage, but no good for drama and especially no good for music videos. Conform will also take you from 24fps to 23.98fps or the other way too - ie film to NTSC film rate and back. And 25p to 24p, for PAL to film and film to PAL. Useful.

Your best bet on the 30.00fps footage is Compressor, with it's motion adaptive optical flow stuff - Advanced frame rate conversions, from 30p to 24p and hope. But it won't help with the shutter speed issue, which will keep the end result strangely video, even though it's at 24p. As I said, you'd get less grey hairs from an HVX 200....

Graeme

In the words of the infamous Winnie the Pooh... "Oh bother."

Good news is, I own a Sony EX1 to fall back too. I'd just need to get a Letus.

Thanks for all the info, gentlemen. I've got to take some time to digest it now.

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Is there a conform I would need to do there or does one second of audio correspond with one second of video regardless of frame rate (I'm not familiar with this at all, having never done it)?

Yes, one second of audio is one second of video regardless of frame rates, but that's not what you're dealing with here. You're taking some number of frames that were shot at 30 frames a second and playing them back at 23.976 frames a second. So a "second" as acquired ? 30 frames ? is not the same as a "second" when played back. In other words, if you shot the hands of a clock at 30 frames a second then conformed down to 23.976, when you played it back you'd discover that one tick of the clock on screen takes longer than one second of real time.

If you were going from 30 to 29.97, it wouldn't be that big a deal. The difference would only be about a tenth of a percent, which would result in a pitch difference that's hard to hear. When 24p material is converted to PAL for air in the UK, for instance, it's commonly just conformed to 25 frames a second, making the audio sound ever so slightly chipmunky. It's something you can notice if you know to listen for it, but it's considered within the bounds of acceptability.

But you're going all the way from 30 down to 23.976, which is a big difference. So the audio will sound really wrong if you just conform it.

You could try digitally stretching it instead, without altering the pitch, but I wouldn't recommend it. You'd get audio artifacts, and everything would still be moving too slowly.

Funnily enough, there are cases where you might want to do this for artistic reasons. I know for some sequences in "The Lord of the Rings," Peter Jackson shot ever so slightly overcranked ? that is, his camera was overcranked, not he himself, though if I had three massive movies to shoot at the same time, I might have been tempted ? to get a very slight slow-motion effect. He then had his actors loop their dialogue against playback, so they recited their lines slightly more slowly than they had on set. In some of the shots the effect really works; in some it kind of falls apart. But them's the breaks.

(Oh, and as for the "23.976" versus "23.98" question, they're synonyms. For some reason, I have the habit of calling it 23.976; others, including the Final Cut UI, call it 23.98. But neither one of them is 24, precisely speaking. If you work on a film project, you're working at exactly 24 frames per second; if you work on a "24p" video project, you're working at 23.976 or 23.98 or whatever your personal shorthand of choice is. And if you're offlining a film project from rushes that were transferred to NTSC video, then you have to be acutely aware of the difference between the two frame rates, because audio sync can become a problem.)

Ok, Jeff. Thanks for that explanation. That settles it then. If they want to use the 5D Mark II and Canon doesn't come out with a firmware update before May, we are just going to do 30p which from my understanding of what you just said is not a big deal to conform down to 29.97. If Canon comes out with a Firmware that allows 24p recording, we'll be good to go as it won't be a big deal to conform to 23.98/23.967. Am I right?

I guess the last question is just to find out if there is a way to make 30p LOOK like 24p without actually changing the speed? Is that what 3:2 pulldown is?

As pointed out, the look of film is as much the 180 degree shutter as the 24fps. The 5D2 always tries to aim for a 1/30th shutter, which is 360 degree in film terms - it's fully open all the time letting the most light in. Nothing you can do to change that afterwards.

Graeme