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Blended frames or repeated frames - which is worse ?

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Rosie Walunas
Blended frames or repeated frames - which is worse ?
on Jan 2, 2013 at 5:41:21 pm

This question is a bit general.

In FCP, I was working with a progressive video in which there were repeated or duplicated frames if one went through the video frame by frame. But, when it came time to convert the frame rate in MPEG Streamclip to meet the project settings, the result was sort of blended frames and ghosting.

This made me realize I don't actually know what is the preferred result in terms of converting frame rates. Editors I've assisted haven't really known the answer as they have other concerns.

I realize that blended frames or ghosting might not be preferred for a colorist and if this is detrimental in terms of quality control, I want to get this right.

Please advise on what 'is best' and how to get to those results. So far, I've worked on projects with mixed frame rates (due to archive materials).

Thanks!


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Alex Elkins
Re: Blended frames or repeated frames - which is worse ?
on Jan 2, 2013 at 6:16:10 pm

Funny, someone else was asking me exactly this question earlier today.

[Rosie Walunas] "Please advise on what 'is best' "

What is best is really neither blending nor repeated frames - converting frame rates through a dedicated hardware converter will do all sorts of clever things to ensure that the results are seamless, whereas doing it using software is always a compromise.
If a software conversion is your only option then (depending on the content) I'd be inclined to say blending. In my experience though, neither looks particularly good.


Another way you could approach this, again content-dependant, would be to use Cinema Tools to conform your material to the desired frame rate. Cinema Tools doesn't convert the files at all, it just tells QuickTime to play them back at a different speed. This can work really well if you haven't got anything that specifically must be shown at exactly the correct speed (someone speaking, for example). For GV/B-roll type stuff, the slight speed change is usually completely imperceptible.


Ideally the frame rate conversions should have been done prior to editing, as you'll now have a fairly labour intensive job to re-connect everything at the different frame rates. Of course, it's not always possible due to time or budget restraints to do this, but it's worth bearing in mind for future reference.


So, in order of personal preference:
Hardware conversion (google 'video standards conversion' or 'Teranex conversion')
Cinema Tools conform (if appropriate)
Frame blending
Frame repeating

Good luck with it.

Alex Elkins
Twitter: @postbluetv
http://www.postblue.tv
Post Blue showreel
Latest work: Greyhounds in Motion at 500fps
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Rosie Walunas
Re: Blended frames or repeated frames - which is worse ?
on Jan 2, 2013 at 6:26:16 pm

Thanks for your response.

So blending / ghosting is 'okay' for color correction? Let's say someone is waving their hand and the frames are blended with ghosting - this is acceptable?

I'd say that the speed factor is important as a lot of the footage is of people talking.

You write, "Ideally the frame rate conversions should have been done prior to editing, as you'll now have a fairly labour intensive job to re-connect everything at the different frame rates. Of course, it's not always possible due to time or budget restraints to do this, but it's worth bearing in mind for future reference."

Does this mean you do agree that the frame rate should be converted to the project's frame rate before editing. This is what has been done, but I have seen on other posts, people suggesting not to convert frame rates and to drop it into FCP and actually edit with multiple frame rates (this as you point out doesn't make sense to me).

Let me know if you have further thoughts.

Thanks.


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Alex Elkins
Re: Blended frames or repeated frames - which is worse ?
on Jan 2, 2013 at 6:53:41 pm

[Rosie Walunas] "So blending / ghosting is 'okay' for color correction?"

Well like I said, in my experience it's not a particularly nice effect. However, from a purely technical point of view there's nothing to say you shouldn't. It isn't going to affect the colours, you'll just have the occasional frame with a rather unappealing frame blend going on. As an editor and colourist myself I'd like to think I'd notice it straight away, but most people viewing it probably won't (or if they do, they won't care), so depending on your audience it may be absolutely fine.


[Rosie Walunas] "Does this mean you do agree that the frame rate should be converted to the project's frame rate before editing."

Yes. I agree with you, particularly as FCP/QuickTime does such a woeful job of the frame rate conversion. Just because you can doesn't mean you should! I've heard (though not tested) that Avid does a much better job.


Out of interest, what frame rates are you converting from and to? If it's just 23.98 to 25 you may still get away with the Cinema Tools method when people are talking. 23.98 or 25 to 29.97 might be too obvious. Do some testing - perhaps you could use Cinema Tools for some of the material and do the frame blending for everything else.

Incidentally, you mentioned that you used MPEG Streamclip for the conversion. You might also want to try running it through Compressor with 'Frame Controls' turned on. It should give you slightly better results. Check out this article for some further information on it if you're unfamiliar: http://www.digitalrebellion.com/blog/posts/using_frame_controls_in_compress...

None of these methods will be better than a hardware conversion, which will be completely imperceptible. All post houses that offer the service will charge per second/minute of footage. If you have the budget you might want to consider converting just the talking head material with them (or the whole lot - go wild!). It's not particularly expensive in my experience - I'm in London and have used a company called Soho Transfer in the past.

Alex Elkins
Twitter: @postbluetv
http://www.postblue.tv
Post Blue showreel
Latest work: Greyhounds in Motion at 500fps
My Vimeo Pro page


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Rafael Amador
Re: Blended frames or repeated frames - which is worse ?
on Jan 3, 2013 at 11:44:23 am

Beside "Next Frame" (repeating frames/linear) and "Frame Blending" for speed/time-base changes, Compressor has two more options based in Vector Interpolation (Optical Flow), but the truth is that this two options most of the time the only they get is to degrade the picture because they process every single frame. "Next Frame" (repeating frames/linear) is the faster and simplest, and quite often is the one that works better.
Repeating frames is not that bad. We do not see how frames are repeated when we see a Hollywood movie (24P) on a normal NTSC TV (29,98).

You can try using directly the p23,97 stuff on a 29,98 sequence, BUT, to avoid frame blending, select the clips on the time-line and left click to access the "Speed Window". Uncheck frame Blending.

About MPGStreamclip, in theory it shouldn't blend frames, unless the you have the "Blend Frames" window checked.

[Rosie Walunas] "So blending / ghosting is 'okay' for color correction? Let's say someone is waving their hand and the frames are blended with ghosting - this is acceptable? "

Yes, "Frame Blending" is a a problem for Color Correction. If you are, for example, using masks to correct some Secondary, the masks will be spoiled in the blended frames.
rafael

http://www.nagavideo.com


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Alex Elkins
Re: Blended frames or repeated frames - which is worse ?
on Jan 3, 2013 at 12:36:54 pm

Rafael's reply goes to show that all of this is a matter of opinion. The bottom line is that very few people would agree that a software conversion is perfect. Often it's good enough though.


[Rafael Amador] "Yes, "Frame Blending" is a a problem for Color Correction. If you are, for example, using masks to correct some Secondary, the masks will be spoiled in the blended frames. "

I disagree with this. You'd have to have an incredibly specific mask for it to be ruined by a bit of frame blending within the shot. It's not ideal, but in my experience it's never, ever been a cause for concern. Certainly if you had someone doing VFX on the shot there'd be plenty of good reasons to avoid blending frames, but for colour correction it would virtually never be a hinderance, in my opinion.

Alex Elkins
Twitter: @postbluetv
http://www.postblue.tv
Post Blue showreel
Latest work: Greyhounds in Motion at 500fps
My Vimeo Pro page


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Rafael Amador
Re: Blended frames or repeated frames - which is worse ?
on Jan 3, 2013 at 2:15:54 pm

As you say, Alex, in one side is a matter of taste, in the other also depends of the kind of footage we are dealing with.
What we agree on, is about that the best results comes from hardware conversion, and with the drop of the prices of the Teranex, that shouldn't be prohibitive option anymore.
rafael.

http://www.nagavideo.com


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Alex Elkins
Re: Blended frames or repeated frames - which is worse ?
on Jan 3, 2013 at 2:24:24 pm

[Rafael Amador] "the best results comes from hardware conversion, and with the drop of the prices of the Teranex, that shouldn't be prohibitive option anymore.
"


Absolutely right. It's incredible how cheap the Teranex is now. The problem I've found seems to be finding a facility with the newer, cheaper Teranex. At the moment most of the places in London are still on the older technology, so are still charging the old prices.

Alex Elkins
Twitter: @postbluetv
http://www.postblue.tv
Post Blue showreel
Latest work: Greyhounds in Motion at 500fps
My Vimeo Pro page


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