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Compressor output losing quality? QTX Deinterlacing?

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Zak Ray
Compressor output losing quality? QTX Deinterlacing?
on Jul 24, 2010 at 12:33:19 pm

I'm transcoding from a 720x480 Anamorphic DV video to a square-pixel ProRes version, and it appears to have lowered the quality-- more than I would think ProRes would. At first I thought it was a QTX display quirk, because it seemed to be applying some sort of blending deinterlace in addition to the quality loss.

Before:


After:


Then I took a look at it in QT7, and the deinterlace seems to be gone, but the quality is still noticeably lower.

Before:


After:


Thoughts?


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walter biscardi
Re: Compressor output losing quality? QTX Deinterlacing?
on Jul 24, 2010 at 12:48:08 pm

Well you're starting out with a very low quality DV original to begin with and then recompressing that to another codec. DV is 5:1 compressed footage and I believe it's 4:1:1 color space so you're missing a lot of information in the picture.

When you convert that footage to another format, it will degrade just as a result of the recompression. When we want to convert formats here, we do this through AJA Kona 3 hardware because it's much cleaner than using software to perform the conversions.

That being said, this is software out there that will do a better job with much more control over the final image than Compressor. Telestream Episode is one, Innobits makes some nice products and Sorenson Squeeze is also a top converter.

Walter Biscardi, Jr.
Editor, Colorist, Director, Writer, Consultant, Author, Chef.
HD Post and Production
Biscardi Creative Media

"Foul Water, Fiery Serpent" featuring Sigourney Weaver coming soon.

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Zak Ray
Re: Compressor output losing quality? QTX Deinterlacing?
on Jul 24, 2010 at 12:56:03 pm

Thanks, Walter. I think there's something else at work though, because when I JUST do a ProRes conversion, there's no degradation. It only happens when I also convert to square pixels. Maybe I'll try working in the Frame Controls?...


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Zak Ray
Re: Compressor output losing quality? QTX Deinterlacing?
on Jul 24, 2010 at 1:09:43 pm

Hm, well boosting the Frame Controls quality seems to have helped the degradation issue. The before and after now both look pretty much the same in QT7.

So I guess the one thing I want to be sure of is, what's happening in QTX? Is it deinterlacing and blending the before? If so, why not the after?


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walter biscardi
Re: Compressor output losing quality? QTX Deinterlacing?
on Jul 24, 2010 at 1:11:04 pm

[Zak Ray] "It only happens when I also convert to square pixels. Maybe I'll try working in the Frame Controls?..."

Well ProRes is not square pixels in SD I don't believe. Been so long since I used ProRes in SD I honestly can't remember and I'm not near an FCP system today.

Set up a ProRes anamorphic SD timeline. What does it say there with the pixels? That's what your setting should be in Compressor.

Walter Biscardi, Jr.
Editor, Colorist, Director, Writer, Consultant, Author, Chef.
HD Post and Production
Biscardi Creative Media

"Foul Water, Fiery Serpent" featuring Sigourney Weaver coming soon.

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Zak Ray
Re: Compressor output losing quality? QTX Deinterlacing?
on Jul 24, 2010 at 1:18:19 pm

Normally you'd be right, ProRes maintains the PAR of it's source which in my case would be DV Anamorphic PAR, but I'm doing this conversion to make a square-pixel version, so I set the resolution to 853x480 and the PAR to 1.0.


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walter biscardi
Re: Compressor output losing quality? QTX Deinterlacing?
on Jul 24, 2010 at 1:51:30 pm

[Zak Ray] "so I set the resolution to 853x480"

That doesn't sound like a resolution that would call for square pixels. Again, not near an FCP system, but 640 x 480 is a square pixel format. 853 would not be a square pixel format so you would want to avoid square pixels I believe.

Walter Biscardi, Jr.
Editor, Colorist, Director, Writer, Consultant, Author, Chef.
HD Post and Production
Biscardi Creative Media

"Foul Water, Fiery Serpent" featuring Sigourney Weaver coming soon.

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Zak Ray
Re: Compressor output losing quality? QTX Deinterlacing?
on Jul 24, 2010 at 1:56:36 pm

Pretty sure 853 is the anamorphic equivalent of 640.


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Michael Sacci
Re: Multiclip
on Jul 25, 2010 at 3:33:03 am

That is the square conversion from 720x480 anamorphic but normally you go down instead of you 720x405 (not 270 as I had it before the edit) might give you better results. But the question that has to be asked is why are you going to a square version of a codec that is meant for broadcast or editing?


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Zak Ray
Re: Multiclip
on Jul 25, 2010 at 11:13:30 am

Wouldn't lowering the vertical resolution mess up the interlacing?

I'm converting them because their only application is to the web, and it's easier for me to work with square pixels for what I'm doing.


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Zak Ray
Re: Multiclip
on Jul 26, 2010 at 11:53:54 am

Is this a bad idea? I mean, they're never going to broadcast and they're never going to be re-cut, I just think it makes more sense to make them square pixels in an increasingly-square-pixel world.


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Zak Ray
Square PAR?
on Jul 28, 2010 at 11:53:28 am

Anyone have any thoughts on this? Is there any reason not to convert my material to square-pixels if it's never going out to broadcast, and likely just the web>


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Michael Gissing
Re: Square PAR?
on Jul 28, 2010 at 12:31:29 pm

Square pixels for the web? yes. Deinterlace for the web? yes

I work in Pal so I make H264 files as 1024 x 576. If I need a smaller pixel size, I work in multiples of that ratio (usually exactly 1/2 so 512 x 288)

Will making a highly compressed resized version affect resolution? yes.


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Zak Ray
Re: Square PAR?
on Jul 28, 2010 at 12:39:33 pm

I'm talking about the master here. Assuming I have a digital master that will never be broadcast, is there any reason not to convert the master to square pixels?

That's all I'm doing-- I'm not touching the interlacing or anything, since that would hobble the quality if I ever wanted to do something with it again. But square pixels seems like a reasonable thing to do to ensure uniformity and prevent misinterpretation by other apps. And I can always change it back, because it's just stretching the PAR.


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Keith Pratt
Re: Square PAR?
on Jul 30, 2010 at 11:40:47 pm

I'd keep it ProRes 720x480 anamorphic 16:9 through the edit and mastering, and only change it to 853x480 when making an H.264 for the web. 720x480 really is the standard for SD, and it's what apps will by default expect. But for the web, you're right, square pixels is the way to go.

Two things:
1: what is your source (DV camcorder, 16mm film scan, etc.) and frame rate?
2: check that Compressor has correctly identified the field dominance in the A/V Attributes tab.


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Zak Ray
Re: Square PAR?
on Jul 30, 2010 at 11:56:02 pm

Good point.

Nearly all of it was acquired from NTSC DV, so I've been just telling Compressor to do lower field rather than even giving it a chance to interpret.


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Michael Gissing
Re: Square PAR?
on Jul 31, 2010 at 12:20:36 am

The master should remain anamorphic as this is a standard that all editing systems work best with and is the broadcast delivery format. Do the anamorphic to square pixel conversion when transcoding and deinterlacing for the web.


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