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Final Cut X Rendering with artefacts no matter what codec

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Andrei Popa
Final Cut X Rendering with artefacts no matter what codec
on Sep 7, 2014 at 5:36:15 pm

Hi everyone,

I have 2 problems while rendering out of Final Cut X.

Artefacts & Controlling the H264 bitrate:


Artefacts:

What I'm rendering has a moving/shaping color background, which gets rendered with wave like artefacts, which can be seen especially in the lower center part if the screen, here is the example (you'll have to watch in on the youtube page to see the artefacts):









It doesn't matter if I use H264, ProRes HQ or even if I export uncompressed, always get the artefacts...

This backround image is an included with Final Cut X Apple Generator, so it should be flawless...

Could this be a bug or poor implementation from Apple?

Bitrate:

How can I control the H264 bitrate, there is a setting that you can set for a max bitrate, but you can't set a minimum or a constant bitrate


So my questions are:

1. How do I render without artefacts?

2. How do I control the bitrate?

3. Does the bitrate matters for digital projection in a cinema, as long as the image looks fine on your computer screen?

Thanks


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Robin S. Kurz
Re: Final Cut X Rendering with artefacts no matter what codec
on Sep 7, 2014 at 7:04:01 pm

[Andrei Popa] "(you'll have to watch in on the youtube page to see the artefacts)"

Hmmm... what does that fact tell you?

Exactly. It's an error on the part of the YOUTUBE encoder. It has nothing to do with FCP. I for one saw no artefacts of any kind.


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Andrei Popa
Re: Final Cut X Rendering with artefacts no matter what codec
on Sep 7, 2014 at 7:43:12 pm

The youtube is just an example, so people can see the artefacts.

The error is in the original file I rendered on my computer as well, it comes out like that when FCPX renders it.


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Robin S. Kurz
Re: Final Cut X Rendering with artefacts no matter what codec
on Sep 7, 2014 at 7:50:20 pm

I don't see how, if the master file doesn't show the artefacts, it could be an FCP issue.


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Charlie Austin
Re: Final Cut X Rendering with artefacts no matter what codec
on Sep 7, 2014 at 7:56:59 pm

[Andrei Popa] " which gets rendered with wave like artefacts"

I've seen this on stuff rendered out of many apps, after effects, FCP, Pr etc. I forget exactly what causes it, but try dropping a gaussian blur on the BG and play with the strength (to shouldn't need too much) and see if that helps.

-------------------------------------------------------------

~ My FCPX Babbling blog ~
~"It is a poor craftsman who blames his tools."~
~"The function you just attempted is not yet implemented"~


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Bret Williams
Re: Final Cut X Rendering with artefacts no matter what codec
on Sep 7, 2014 at 9:24:30 pm

Did you look at the video? Nice smooth grads. I didn't see any problems either.


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Robin S. Kurz
Re: Final Cut X Rendering with artefacts no matter what codec
on Sep 7, 2014 at 9:33:19 pm

[Bret Williams] "Did you look at the video? Nice smooth grads. I didn't see any problems either."

I can only assume he means in the lower res/quality versions directly on YouTube. In which case, as I said, that's not an FCP issue.


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Bret Williams
Re: Final Cut X Rendering with artefacts no matter what codec
on Sep 7, 2014 at 9:34:57 pm

Which is precisely why I asked Charlie the question.


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Robin S. Kurz
Re: Final Cut X Rendering with artefacts no matter what codec
on Sep 7, 2014 at 9:37:58 pm
Last Edited By Robin S. Kurz on Sep 7, 2014 at 9:39:50 pm

Which is precisely why he wrote "(you'll have to watch in on the youtube page to see the artefacts)" because you (and he) can't see the artefacts in that (full res) version.


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Bret Williams
Re: Final Cut X Rendering with artefacts no matter what codec
on Sep 7, 2014 at 9:45:59 pm

Charlie never said that. He said "I've seen this on stuff rendered out of many apps, after effects, FCP, Pr etc. I forget exactly what causes it, but try dropping a gaussian blur on the BG and play with the strength (to shouldn't need too much) and see if that helps."

And SO, I asked him if he had actually watched the youtube video which looks completely fine. So there is no need to do what Charlie suggests, unless his view of the video was different or he was just going by the OP description and the horrible looking freeze frame youtube is showing.

It looked crystal clear in 720p here.


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Robin S. Kurz
Re: Final Cut X Rendering with artefacts no matter what codec
on Sep 7, 2014 at 9:59:19 pm

[Bret Williams] "Charlie never said that. "

Since you did not use any sort of QUOTE, which is always useful for avoiding misunderstandings, I could only assume you were addressing the OP.


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Charlie Austin
Re: Final Cut X Rendering with artefacts no matter what codec
on Sep 7, 2014 at 9:52:09 pm
Last Edited By Charlie Austin on Sep 7, 2014 at 9:54:43 pm

[Bret Williams] "Did you look at the video? Nice smooth grads. I didn't see any problems either."

I did, the blob edge gradient looks fine at 720 on YT, but I think I see what he's talking about if you look at the non-colored area. (kind of moving graininess?) That's why I suggested a slight blur. Honestly I don't know where in the chain it's coming from, it may well look like that in the generator source and just not show up in the X UI.

-------------------------------------------------------------

~ My FCPX Babbling blog ~
~"It is a poor craftsman who blames his tools."~
~"The function you just attempted is not yet implemented"~


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Andrei Popa
Re: Final Cut X Rendering with artefacts no matter what codec
on Sep 7, 2014 at 11:36:43 pm

Hi guys,

Thanks for the replies.



Robin

I think you did not read properly my initial post nor my reply. I said that the master file shows the artefacts.

Bret

If you look at it carefully there are artefacts, Charlie described it best as "kind of moving graininess" it's more like lines / waves or waves of lines as opposed to the traditional square artefact.

These artefacts appear in the center about midway between the writing and the bottom of the screen.

It's not so bad, but it shouldn't be there, and if projected on a big screen it may look worse...

Charlie

That background is a generator that comes with Final Cut X. It does not have any blur function/control on it.

I find it very odd, because there shouldn't be any problem at all, especially since it's a built in generator, it's not third party plug-in or a video file.

So my only explanation is FCPX is messing up...

Of course I'd prefer to fix it but I'm not sure it's possible...

P.S. I watched it carefully inside FCPX after I wrote the above, and the artefacts are there as well, I don't have any other effects plugins on this generator, so I guess it's a FCPX mess-up...

Last but not least:

1. Is there any way to specify a fixed bitrate in FCPX or Compressor (fixed bitrate, not maximum bitrate limit)

2. This clip is about 7mbps at 720P

Is 12mbps at 720P make any difference on a big screen?

Theoretically it should, but if it's crisp at 7mbps on your computer screen isn't it going to be the same in the cinema?

The cinema screen will be way bigger, but the projector will still be putting out 720P...


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Bret Williams
Re: Final Cut X Rendering with artefacts no matter what codec
on Sep 7, 2014 at 11:53:31 pm

In compressor just use one pass CBR. 5000kb/sec should be fine for 720. But if the artifacts are there in the generator, then they're going to be there on output. I'm really not seeing anything worth worrying about. But why not follow Charlie's advice and add blur. You just add a blur filter to the generator. Gradients are the hardest thing for compressors to do. And it could look perfect in your file, but still break up with banding on another screen because it's only an 8bit panel vs a 10bit panel. An off example, my iMac can't tell the difference between 100% white and 110% white. It displays both as the same. But on my Flanders video monitor, they are significantly different shades. I'd say if anything, the projection of your project would be slightly less sharp than your computer screen .


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Andrei Popa
Re: Final Cut X Rendering with artefacts no matter what codec
on Sep 8, 2014 at 12:05:55 am

It seems I haven't read Charlie's post correctly, he said I should add a blur and I understood I should remove it...

I tried it, and it doesn't seem to do much, but it is a good idea...

Where can I find the one pass CBR setting in Compressor? I know it exists inside Adobe Media Encoder, but can't find it in Compressor for .mov containers...

"the projection of your project would be slightly less sharp than your computer screen"

I guess a higher bitrate will make it sharper on the big screen...


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Walter Soyka
Re: Final Cut X Rendering with artefacts no matter what codec
on Sep 8, 2014 at 12:42:54 am

The problem you are seeing is called banding.

Here's a detailed explanation I wrote up for a related post some time ago in the Ae forum:

http://forums.creativecow.net/thread/2/1023784#1023815

Basically, as Bret was saying, the problem is that the tone difference is too subtle for your display to show. If you have have only 256 possible gray values (8-bit color), and you're covering only a very small range of those 256 possible grays over a large area, you'll get hard edges as the codec or display "clicks" over from a gray of say 200 into the next neighboring gray of 201.

You cannot blur your way out of banding; the line from 200 to 201 doesn't go away, because your color depth is limited somewhere. Quite the opposite: you have to add a little bit of noise to dither or perceptually break up the hard edge. Decreasing the subtlety of the tone may also help if your design allows.

Walter Soyka
Designer & Mad Scientist at Keen Live [link]
Motion Graphics, Widescreen Events, Presentation Design, and Consulting
@keenlive [twitter]   |   RenderBreak [blog]   |   Profile [LinkedIn]


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Andrei Popa
Re: Final Cut X Rendering with artefacts no matter what codec
on Sep 8, 2014 at 12:48:58 am

Hey Walter,

Noise seems to work...

Thanks!

I love these things (technical quirks that you would never think about and are the exact opposite of what you'd expect)


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