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Small bug: REC709 vs REC601 in FFMPEG ProRes/DNxHD recordings
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DWAM  
#1 Posted : Wednesday, January 4, 2017 2:41:25 PM(UTC)
DWAM

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Hi Martin!

I noticed lately that recording HD and FullHD video in prores and dnxhd through FFMPEG/vMix does not conform to the specs. I know it is an FFMPEG issue that can be fixed.

When you record 720 or 1080 videos with vMix, you get REC601 or ITU-R BT.601 which is supposed to be SD video, thus incorrect. We should be in BT.709 color space.

I have faced this issue when simply converting videos, I think you should add parameters to your commandline depending on resolutions :

ex:
ffmpg in -color_primaries bt709 -color_trc bt709 -colorspace bt709 out

For VC3 I remember (not checked if it is still the case) it was necessary to use the -vf colormatrix=bt601:bt709 -pix_fmt yuv422p switches to encode/transcode correctly...

Here's a forum's thread I used to fix this issue years ago :
http://community.avid.co...t/60895.aspx?PageIndex=2

Hope this helps. I think this problem should be solved for obvious quality reasons. Where's the point in recording 4:2:2 if the color space is wrong ?

Thanks for everything. I love vMix !

Best wishes to all of you for 2017

Guillaume
DWAM Bordeaux France
http://www.captnstream.com/
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Squier on 1/4/2017(UTC)

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admin  
#2 Posted : Wednesday, January 4, 2017 10:09:33 PM(UTC)
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Hi,

vMix most definitely does export Rec709 correctly for all recording formats including FFMPEG.
See attached screenshot.

This shows colour bars side by side with a ProRes MOV recording of those colour bars recorded in vMix.
Showing them side by side confirms it is Rec709.

If you are not seeing this, please do the same test then go to Settings -> About and Send Support Report
then email us at info@vmix.com.au and we can advise what setting might be misconfigured.

Thanks,

Martin
vMix

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DWAM  
#3 Posted : Thursday, January 5, 2017 9:25:29 AM(UTC)
DWAM

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Sorry Martin, I was not clear enough.

I'm not saying vMix does it wrong, I'm saying that FFMPEG does not write the correct color space information in the recorded files.
You can check this easily on ProRes and VC3 files by using Mediainfo for instance.

I understood this is a known issue with FFMPEG...

Let me know if you want more details

Thanks for your concern
Guillaume
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