I have discovered that if I export a 10 bit DPX at legal level from my standard Avid Rec 709 4K 4096_2160 project that DPX will be misinterpreted in Resolve 15 with the Clip Attribute set to "Auto" Data Level. Manually setting the Clip Attribute to video and everything looks fine, of course this makes sense because the DPX was exported as legal from Avid. What I don't understand is why in Auto Resolve doesn't register that the DPX is legal. I would assume there is some sort of metadata flag that lets programs know what the video essence level is legal vs. full range. Does Avid not create a standard metadata flag for this or is Resolve not understanding Avid's version of the flag, if there is one?
In the process of testing this I learned the Black Magic Express will play DPX straight out my DNxIO, I had only used it for .movs before and even then it only works with certain codecs. Interestingly even though Resolve with Auto Data mode plays back the legal DPX wrong, in essence adding a Full Range to legal scale to the DPX which is already legal resulting in a black level of 64 on the Resolve scope and a black level of 50 mV on an external scope, when the legal level DPX is played through Black Magic Express the level is correct on the scope. As far as I know BM Express does no scaling so playing a file through it should be a clear representation of the video essence of the DPX file as far as I know. To me this proves that the DPX is in fact legal video essence.
Testing further I then exported the same sequence checking scale to Full Range in the DPX export window in Avid. The resulting DPX plays correctly in Resolve with Clip Attribute set to "Auto" or "Full" and looks scaled down when set to video. This all makes sense. But when I play the Full Range DPX in BM Express the levels still look correct for Rec 709. If BM Express plays un-scaled video essence I would expect the Full Range DPX to have black well below 0mV and over 700 mV if the video essence is truly Full Range in the Full Range DPX export from Avid. Similarly AMA linking to both Full Range and Legal DPX exports back into Avid show virtually the same levels correct for Rec 709, there is a slight shift in color bar 100% boxes in the smpte 219 color bars but not the kind of overall level shifts I would expect from a Full range vs. legal level comparison.
Does this mean that when I check Full Range in the Avid DPX export box that the video essence still remains legal but a flag is put in some sort of DPX header/metadata that informs programs to scale the legal video essence to full range. If the Full Range DPX export is really creating Full Range video essence in the DPX then why is Black Magic Express playing it at proper Rec 709? As I already mentioned I've been told over the years BM Express is a direct representation of the a files video essence level. Also I've always been told that if I ama link in Avid and make sure there is nothing in source settings in the way of a lut or scaler then Avid shows the true video essence of that file. If these two things are true then I assume a Full Range DPX export from Avid isn't really scaling the actual video essence.
It's hard to sort through what's really going on under the hood. Anybody got any suggestions? I'm sending this question to Avid directly too.
John Moore Barking Trout Productions Studio City, CA bigfish@pacbell.net
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Posted by: John Moore <bigfish@pacbell.net>
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