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Old 1st February 2016, 16:51   #1  |  Link
ron spencer
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MeGUI Colour Space Warning

Hey all,

I have been learning with fun how to make bluray compatible output with MeGUI. Not so hard.

But I have an issue. I am starting with DNxHD files that are YUV output. MeGUI gives me a warning before I encode to change the color space to YV12. My output files are YUV. So why is MeGUI wanting to convert to YV12? Not sure if this alters the final quality or not, but if it does I'd like to fix it. The only AVISynth command used is a crop. So not sure why this warning pops up as the end output is YUV, the same as the source.

thanks
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Old 1st February 2016, 17:00   #2  |  Link
poisondeathray
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Different chroma subsampling for YUV ; DNxHD is usually 10bit 4:2:2 (but there are other variants), Blu-ray only supports 8bit 4:2:0
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Old 1st February 2016, 19:21   #3  |  Link
ron spencer
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by dnxhd is 8 bit...and you are right, it is 4:2:2 for chroma sub-sampling. But is it a waste to change colour space from YUV to YV12 and then back to YUV? I guess I need to to get to 4:2:0. Will this introduce any quality issues? I don't see any I think.
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Old 1st February 2016, 19:33   #4  |  Link
poisondeathray
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Quote:
Originally Posted by ron spencer View Post
by dnxhd is 8 bit...and you are right, it is 4:2:2 for chroma sub-sampling. But is it a waste to change colour space from YUV to YV12 and then back to YUV? I guess I need to to get to 4:2:0. Will this introduce any quality issues? I don't see any I think.
YV12 is YUV. Think of "YUV" as the broader family. YV12 is a subset of YUV, specifically 4:2:0 planar. YV12 is required for BD

http://www.fourcc.org/yuv.php

The only things to remember in avisynth are if your content is interlaced, you must use the interlaced=true switch, and the correct matrix (usually Rec709 for HD and 601 for SD) if coming from a non YUV source
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Old 1st February 2016, 22:10   #5  |  Link
ron spencer
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ok thanks.

So if my source is 4:2:2 and 8 bit, YV12 converts it to 4:2:0 for bluray.

So my last question

Media info reports my encoded file (with right tags for Rec709 via MeGUI) as YUV. Is it right that is reports this as opposed to YV12 as you said YV12 is required for Bluray? Or is it just stating YUV as the broader family?

thanks for your input!
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Old 1st February 2016, 23:32   #6  |  Link
poisondeathray
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Quote:
Originally Posted by ron spencer View Post
ok thanks.

So if my source is 4:2:2 and 8 bit, YV12 converts it to 4:2:0 for bluray.

So my last question

Media info reports my encoded file (with right tags for Rec709 via MeGUI) as YUV. Is it right that is reports this as opposed to YV12 as you said YV12 is required for Bluray? Or is it just stating YUV as the broader family?

thanks for your input!

I think it' s just reporting the broader family (and it can make mistakes, I wouldn't rely on it to heavily)
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Old 2nd February 2016, 22:36   #7  |  Link
ron spencer
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Quote:
Originally Posted by poisondeathray View Post
I think it' s just reporting the broader family (and it can make mistakes, I wouldn't rely on it to heavily)
Ok...still have one final question.

I am using 1080i files...MeGUI is telling me I need to append converttoyv12() to the end of my avisynth script, which is good. But it does not add in interlaced=true, even though I have specified it as TFF in my initial MeGUI setup for this job.

So, do I need to edit the script before running the encode to say:

Quote:
ConvertToYV12(interlaced=true, matrix="Rec709")
If so, any reason why MeGUI does not append the interlaced=true, matrix="Rec709"...is it because my source is already YUV?

I still find it odd that I would go from YUV 4:2:2 --> yv12 4:2:0 --> YUV 4:2:0


I am using the Rec709 option in my x264 encodes.

thanks

Last edited by ron spencer; 2nd February 2016 at 22:40.
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Old 2nd February 2016, 23:27   #8  |  Link
poisondeathray
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Quote:
Originally Posted by ron spencer View Post

I am using 1080i files...MeGUI is telling me I need to append converttoyv12() to the end of my avisynth script, which is good. But it does not add in interlaced=true, even though I have specified it as TFF in my initial MeGUI setup for this job.
--tff is an x264 encoding setting which occurs after the script . It also has no accurate way of determining if something is interlaced or not (it can make mistakes). User must determine that. I haven't used megui for a long time, but if it's something you think should be improved you can add a feature request

Quote:
So, do I need to edit the script before running the encode to say:
ConvertToYV12(interlaced=true, matrix="Rec709")
You don't need the matrix, coming from a YUV source. The matrix is only for RGB<=>YUV conversions, but you do need interlaced=true because the chroma planes are resized . But it doesn't "hurt" to leave the matrix argument in; it's just a no-op


Quote:
I still find it odd that I would go from YUV 4:2:2 --> yv12 4:2:0 --> YUV 4:2:0
In this case, it's just YUV 4:2:2 to YV12

YV12 4:2:0 is YUV 4:2:0 . But YUV 4:2:0 is the broader term. YV12 specifies a specific arrangement and byte order. For example NV12 is also YUV 4:2:0 . So YUV 4:2:0 is the broader category, and YUV is the broadest (it includes other subsampling 4:2:2, and no subsampling 4:4:4, plus all their derivatives and plane arrangements)

Last edited by poisondeathray; 2nd February 2016 at 23:31.
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Old 2nd February 2016, 23:48   #9  |  Link
ron spencer
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OK I get it...thanks for teaching me something useful. I can just add the interlaced=true. Maybe request feature of megui that if in the initial avs setup I specify interlaced, it should add in the interlaced=true part.

Cheers and thanks again!!!
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