As far as I know, Avid systems (or at least their operators) expect all
values to be within 709-legal range (16-235). Thus, our default workflow
involves a slight range compression for output passes that are being
delivered to editorial, and these are then encoded using Nuke on OSX using
the 709 "levels".
Now, as far as ffmpeg goes, unless something has changed recently, it uses
the 601 primaries to do its RGB -> YUV conversion when encoding, while the
Avid codec decodes using the 709 primaries. Ideally, you would compensate
for this beforehand using a matrix or similar (I had one laying around at
one point...), but you can get ffmpeg to do it for you by adding this to
your conversion options:
-vf colormatrix=bt601:bt709
However, I've heard whisperings that this can cause its own set of problems
based on when it occurs during the conversion process (after the input is
sampled into macroblocks).
Anyway, this is a little bit of a brain-dump, but hopefully some of it is
useful.
-Nathan
-----Original Message-----
From: aaron barclay
Sent: Saturday, March 29, 2014 5:13 PM
To: Nuke user discussion
Subject: [Nuke-users] DNxHD from ffmpeg
Hi,
a bit off topic as I am not wanting to write DNxHD straight from nuke,
however the encoding problems I am having are most likely to have been
encountered in a nuke -> editorial pipeline.
Is anyone encoding DNxHD via ffmpeg and if so how are you dealing with
the different "levels", 709 or RGB.
Seems like a common problem for vfx delivery but I don't find a lot of
recent info about it. Any help greatly approciated!
aaron.
ps - also in my defense for off topic - I am totally calling the
ffmpeg in a subprocess from nuke after the images are prepped!
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