Wow I sent this one yesterday and it shows up now. I've notice my last reply to this thread from today hasn't popped up either but others have from today and now this one shows up from yesterday. Funky town on the internet.
---In avid-l2@yahoogroups.com, <bigfish@...> wrote :
I've asked several forms of this question in the past but today I have a specific request from the truck engineers for a live show we are prepping playback elements for. For starters we've shot primarily with Alexa, I know that horrible camera that isn't even Netflix 4K worthy, but we are doing HD 23.976 transcoding to DNX 175X for offline and online given our quick turn around. We are baking in the LogC to Rec 709 LUT and all looks fine. We always work Rec 709 in Avid as it's the broadcast standard for all our deliveries.
Now the truck person wants us to deliver 59.94i files in DNX-145 8 bit RGB files. Well for starters DNX-145 is only 8 bit so that is a no brainer. 59.94i is also understandable as this will be a live broadcast in the US. It's the RGB that is confusing me. I have done the mixdown in the 23.976 project to DNX 115, which I assume it the DNX-145 equivalent just like DNX-175X is the DNX-220X equivalent, and then opened a 59.94i with all the motion adapters and modification to the mixdown sequence. I then export a QT movie with custom set to DNX-145 Upper field and click RGB to comply with the requests. Now the resulting file is 59.94i but when I ama link to it the levels of color bars come back in perfectly. Given it is an Avid codec I have no ability to change the source settings from 709 to RGB to see if there is a difference. Given I've always understood the ama link to bypass the QT engine and therefore display the true video essence of a file I would expect if I had truly exported to RGB levelsI would be seeing color bars going way below 0 millivolts and way over 700 mV just like I do when an RGB level file is imported as if it is 709 and not scaled into legal range. Doesn't this mean the real video essence in the supposedly RGB exported file is still 709 levels.
I also used Adobe Media Encoder sending a QT ref file from the 23.976 project and setting it's levels to RGB and also a 2nd QT ref set to 709. Once baked out of AME with the pulldown added the QT Ref exported at RGB level comes back ama linked in Avid at perfect levels while the QT Ref exported with 709 level checked comes back ama linked low in level. This behavior is common for me when using AME so I always check RGB when exporting QT ref to AME. Bottom line is once again the RGB exported QT ref once processed in AME yield the correct levels when ama linked back into Avid. So to me that means the actual video essence is still 709.
I'm waiting to hear back if the AME file will be acceptable. I'm beginning to think that the behavior I see in AME with regards to checking RGB vs 709 level is indicative of how other types of software read files and maybe the gear on the truck needs the metadata flag set to RGB to properly handle a file which is really 709 in video essence. I'll report back when I find out but apparently the truck person is being very uncooperative about questions as to why they want a "RGB" file and not the ubiquitous 709 standard that is what the network that is airing the live show wants when we give them files. What kind of truck playback system doesn't work with 709 video levels? I also get suspicious of tech specs that request DNX-145 8 bit given 145 is only 8 bit. What's next a tip penetration spec on the file?
On a related topic. I never work in RGB projects as all my work is broadcast but if I were to work in an RGB project how do I properly monitor that in my Tek wfm-7020 and Rec 709 program monitor. I see when I'm running Ver 8.5.2 when I change the project color space things change drastically with 2020 shifting hue on the vector scope, which is the way the math works as far as I know. When I switch to and RGB project the levels jump well below 0 and over 700 so what is one to do when scoping and RGB show. I will have to look but I don't recall and RGB mode on my scope, something akin to choosing 100 percent bars over 75 percent in the vector scope setting. And what would be a compelling reason to work in RGB space. I think that is common in 444 projects but I don't have in practical experience or need to work those projects yet.
John Moore Barking Trout Productions Studio City, CA bigfish@...
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Posted by: bigfish@pacbell.net
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this is the Avid-L2
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