60p for "normal" 29.97 work

[Jeffrey Butler]

I'm wondering about 60p workflow for video that will wind up at 29.97 (possibly even SD downconvert).

I want to shoot as much detail as standard op as possible, and love the option of super clean slo-mo. But does that mean I should shoot at 60p and work at 60p, then output an NTSC version after the fact?

I know it depends on output - but - my question isn't as much about output as it is - will shooting 720/60p give me the most flexibility and the best quality, without hamstringing me for SD output....even HDDVD output?

I'm still trolling around the forum, but am looking for the best long/term highest quality/most flexible capture options for later output...and assume that's 720/60p. Am I close? I guess another way to ask that - When wouldn't I shoot 60p? I'm sort of assuming that w/ 720/60p I can get to anything else....

[Stephan Ahonen]

Unless you're actually going for the look of 30p, I recommend aquiring 60p for SD downconvert. Even though the frame rate of NTSC is technically 29.97 fps, interlacing gives it an effective temporal resolution of 59.94 Hz, so in order to make your material indistinguishable from native NTSC material you will have to aquire at that temporal resolution.

If you are actually going for the 30p look then I'd personally shoot straight 30p.

FYI, in the HDxx0, 24p, 30p and 60p actually mean 23.98, 29.97, and 59.94 fps respectively.

[Jeffrey Butler]

Originally Posted by Stephan Ahonen

FYI, in the HDxx0, 24p, 30p and 60p actually mean 23.98, 29.97, and 59.94 fps respectively.

Ok...29.97 frames per sec = 59.94 fields per sec, but a progressive frame (one not interlaced) is still running at (for NTSC) 29.97 fps, but not 59.94 anything/per sec, or no wait - that's what NTSC is, so the conversion to NTSC will always yield those frames/fields/per/sec.

But yeah, you answered my question - shoot at 60. Work at 60, then convert it as you need it. I'm going to have to really look more into working at 59.94 and getting back to 29.97. I'm assuming you can still have some great slo-mo, even working in 60....

Thanks.

[Stephan Ahonen]

Sure, sports broadcasts do slomo from 60i/p sources all the time. Going down to about 2/3 original speed is the lowest you can go and still look really smooth in my experience, 1/2 speed looks acceptable, start going below that and you'll only really want to be using it to emphasize something really tiny.

[Werner Wesp]

I have tested this, i.e. shooting in 50p and undersampling it to 25p just to see what it looks like. Shooting 50p gives me the opportunity to have super smooth slowmotion of any particular instance - but the final edit should be just 25p. It looks fine as soon as you turn off the resampling that your NLE might do (otherwise you recreate the motion smoothing, which you perhaps don't want to...). Everything will look like 1/120 shutter, because that's what I used to recreate the natural looking slowmotion (as it were 25p with a shutter of 1/60)...

[Jeffrey Butler]

I'm curious about shooting 60fps then dropping the footage into a 30fps timeline - I'm guessing I'll have to render it at somepoint, but perhaps there's a conversion (like Cinema Tools?) to run on all the footage first? I'm thinking CT will be helpful, but I'm not certain it's a general frame rate modification tool...

[Jeffrey Butler]

Anyone else shooting 60/50 for 29.97/25 use? I really want to shoot 60fps, but I'm looking out for good reasons to NOT do so...

[Stephan Ahonen]

I'm seeing a lot of misunderstanding here about the meaning of a 29.97 fps frame rate as it applies to television. Standard definition video is interlaced, which doubles the temporal resolution of the video. If you want to shoot HD and have it hold up in standard def, shoot at the field rate of the standard you're downconverting to, not the frame rate! NTSC shooters should shoot 60p, PAL shooters 50p, and you should use a 1/60 or 1/50 shutter unless you are intending to take freeze frames (not slomo, actual freeze frames) from the footage.

[Jeffrey Butler]

Originally Posted by Stephan Ahonen

If you want to shoot HD and have it hold up in standard def, shoot at the field rate of the standard you're downconverting to...

That's the answer I'm looking for here. I get frames vs. fields, but as a constuct to say "when considering which framerate to shoot given that you're going to deliver NTSC at some point, but want to retain the highest quality footage, shoot the field (temporal) rate, not the frame rate" - is a reason that gives me confidence in my current desire to shoot 60fps (and probably only) - I want to shoot 60 - I plan to shoot 60 - but your answer just then helps me see why I can get away with always shooting 60... =)

I'll leave the (and other temporal variants) alone for now. I've got NTSC in my blood, and just want to transfuse HD(V) in there...at the moment there's not a single HD DVD player "on my block," so while I want to work in HD for the next 18mo's I'll deliver in SD - but when it's time, I can offer an HD version of the old stuff. Just like the film guys can now...(of course that's independent of the framerate discussion here).

[Werner Wesp]

If you want to output SD 50i, you can obviously best shoot in 50p. your footage won't be as sharp as SD 25p, because of the interlacing. I just always want to output 25p HD (for several reasons), but originating in 50p gives me quite some advantages: super slow-motion etc. The footage I don't slow down wont be handled without any filter (that would mimic the motion smoothing, and I don't like that) - I just drop each other frame. So what I shot in 50p with a shutter of 1/120, does look like 25p with a shutter 1/120 - and what I slow down (that's also shot in 50p with a 1/120 shutter) looks like natural 25p with a 1/60 shutter.

The only catch in that workflow is that you have to follow the rules for shooting 25p while you're actually shooting 50p (which is obviously a lot more forgiving on movements)...

[Stephan Ahonen]

Originally Posted by Werner Wesp

If you want to output SD 50i, you can obviously best shoot in 50p. your footage won't be as sharp as SD 25p, because of the interlacing.

25p is just as interlaced as 50i when it hits the air. That is, the entire broadcast chain from the point it gets downconverted to SD to the TV in someone's home is painting lines in alternating odd/even order. Your 25p footage will be treated exactly the same way as any regular 50i footage all the way through that broadcast chain. Static shots in 25p will look just as sharp as the same shots in 50i, and moving shots (where interlacing technically loses vertical resolution) lose resolution anyway due to motion blur, so the effect cancels out.

To help understand this a bit, realize that SD video doesn't care about frames. Say you're editing linear, jogging through analog tape (if you've never done this, then you don't know a thing about real editing). If you freeze framed at a point where there's motion in the frame, you'd see the subject strobing back and forth as the monitor drew the odd and even fields that captured different moments in time. Now say you had a tape in the machine with progressive content on it. Even with progressive content you could still get that effect by jogging the tape to a point where it's drawing the odd field from one frame, and the even field from another. SD isn't drawing interlaced frames, it's drawing fields. That's why progressive content in an interlaced system is truly no different than native interlaced material.

Different looks for different applications, of course, if 25p is the look you want, go for it. But if your target is TV broadcast, especially if your footage is just part of the final edited program, you really want to match the motion characteristics of the footage that's going to be airing directly before and after you. That includes using a 1/50 or 1/60 shutter. I only go to a higher shutter speed when I'm in super-bright sun and the camera's ND filter isn't cutting it.

[Steve Mullen]

Originally Posted by Stephan Ahonen

Now say you had a tape in the machine with progressive content on it. Even with progressive content you could still get that effect by jogging the tape to a point where it's drawing the odd field from one frame, and the even field from another.

Depends on what you mean by MONITOR. If the monitor is an HD monitor that displays FRAMES -- there will be no fields displayed. Since that is how folks "monitor" HD, they will never see what you describe. Nor will they see it on their computer "monitor." Nor, on a 480p "monitor."

It is the conversion of P to I that MAY create temporal artifacts.

For example, if you down-scale each 1280x720 frame to a 720x240 field you will have converted 720p50 to 480i50. Because the PAL frames will have fields that were captured 1/50th second apart -- there will now be temporal artifacts. It will look just like 50i video.

However, if you down-scale every-other 50p frame -- then each 1280x720 frame becomes a 720x480 frame. It will have NO temporal artifacts. As this PAL video passes through the 50i chain, NO temporal artifact will be created. It will look just like 25p film. It's progressive (NO temporal artifacts) nature will be preserved.

You can also convert P to I using 2-3 pulldown which creates yet another "look." Thus, it is the conversion process that determines what one sees.

[Justin Ferar]

Hey Steve,

Does your book talk about downconverting 720p60 to NTSC DVD? Specifically preserving the progressive frames by creating a 480p DVD as opposed to a 480i DVD?

I'll be in the same boat as Jefferey (original post) as I will begin editing our HD projects (720p60) in a few weeks as all the SD projects are just about finished. As of now all of my clients have HD televisions with standard def DVD players.

Anyone else creating 480p DVD's from 720p60?

What's your flow?

[Stephan Ahonen]

Originally Posted by Steve Mullen

Depends on what you mean by MONITOR. If the monitor is an HD monitor that displays FRAMES -- there will be no fields displayed. Since that is how folks "monitor" HD, they will never see what you describe. Nor will they see it on their computer "monitor." Nor, on a 480p "monitor."

Maybe you should have read my post. I was talking about linear editing on analog tape. What kind of monitor did you think I was talking about?

Don't forget that there's an interlaced HD standard. Folks editing 1080i are still seeing interlace flickers in their 50i freeze frames. Since they're all editing digitally they can't step through field-by-field like you could with analog, so they can't see the fact that 25p material still has interlace issues on frame boundaries. The software won't let you see it.

Anyway, I was trying to illustrate the fact that there's no such thing as eliminating interlace flicker in an interlaced system. Even if you shot progressive, every 1/25th or 1/30th of a second the system will paint the odd field of the next frame while the even field of the previous frame is still visible. Guess what, that's an interlacing artifact. You haven't eliminated them, you've only reduced them at the expense of making your motion all juddery. Interlaced systems don't care about frames! Your progressive material is just another series of fields as far as the broadcast chain is concerned. Which is exactly what you would have gotten out of my previous post, had you read it.

If you still need proof, put a thin horizontal line on the screen. See it flickering?

For example, if you down-scale each 1280x720 frame to a 720x240 field you will have converted 720p50 to 480i50. Because the PAL frames will have fields that were captured 1/50th second apart -- there will now be temporal artifacts. It will look just like 50i video.

Why is this a bad thing? Everything on TV in PAL land is 50i video. People have been watching 50i for decades, and guess what, they're used to it. From a technical standpoint, yes, progressive scan is superior to interlacing. From an aesthetic standpoint, if you're not specifically going for the 25p look (and if your look in HD is 50p, I would argue that 25p is not how it's meant to be seen), there is absolutely no reason not to go with the 50i look that viewers are used to and expecting. 25p provides no actual visual benefit, and can actually look much worse due to low temporal resolution.

[Werner Wesp]

Originally Posted by Stephan Ahonen

Why is this a bad thing? Everything on TV in PAL land is 50i video. People have been watching 50i for decades, and guess what, they're used to it. From a technical standpoint, yes, progressive scan is superior to interlacing. From an aesthetic standpoint, if you're not specifically going for the 25p look (and if your look in HD is 50p, I would argue that 25p is not how it's meant to be seen), there is absolutely no reason not to go with the 50i look that viewers are used to and expecting. 25p provides no actual visual benefit, and can actually look much worse due to low temporal resolution.

50i is what is aired in europe, indeed. But if you produce SD for a DVD, you can make progressive MPEG2 files. Most people are looking at the DVD's with a large LCD or Plasma that's also progressive in nature - so since the total chain supports progressive, the image will be sharper since there's no necessity to calculate intermediate values for 2 lines/fields. On top of that, the MPEG2 will handle the progressive footage a lot better and no need to watch the (probably horrible) de-interlacer of the monitor or TV working...

By the way - I'm not saying 50i is a bad thing. Not at all. I just like progressive better. I like the look of 25p over 50i, because of the crispness and steadiness. If one is into absolute fluid motion (not minding slightly lower resolution and not minding the fact you can NOT watch it decently on a home LCD or Plasma), 50i might suit better.