As per my post on the MAC forum where a user seems to have bumped into this problem (post copied below):
The project is a 1080 50i PAL project that, to date, has vision from our P2 cameras in it. Enter our new DVX 200 4K. We have this set up for UHD 50p on internal cards (so 4:2:0 or 4:0:2, cant remember). Bringing in the vision:
AMA link to folder
Transcode to 1080 50i - no need to hog RAID space when it isn't needed. See below:
mmmmm, nice... NOT!
Then tried setting the project to UHD 25p and transcoding to DNxHR 25p (no 50p option - the project is 50i so 50p is greyed out)
YUK! These stills show both fileds - looks even worse when paused but understandable. So we played with various frame flex options and the results were the same.
Next - don't use transcode, use "import":
same result as the "transcode" to DNxHR HQ 25p - better than the "transcode" to DNxHD 50i but still not good.
Finally, use "import" to bring it in. Project is set to 1080 50i during this step:
Yay, we have a winner, nice smooth lines. Incidentally, using Adobe Prelude/Media Encoder to transcode the 4K to DNxHD 50i also produces this nice clean result.
So I think the "transcode" engine is broken and not doing a good job. Naturally I want to use "AMA Link/Transcode" as it is twice as fast bringing the vision in using the "Import" option. A 30" clip takes under a minute using this method compared to 2 mins for import... (btw the Dual Xeon is on this years shopping list..)
We have fiddled with the settings available on the Transcode dialogue, trying different DNxHD settings, 10bit, 185 etc and the results are always the same. I am keen to hear any thoughts others have had with this. Moving forward, some of our projects will be native 4K 50p but lots wont be and we'd rather collect vision at 4K for future projects than set the camera to its 1080 settings.
Here is the earlier email:
Hi all - I've just run headlong into the 4K 50p > 1080 50i aliasing issue with vision shot on a DVX200. Jaggy lines when the vision is transcoded down to 1080i.
#1
Project is 1080 50i (historic project with P2 HD in it)
AMA link to 4K 50p external HDD
horizontal fine lines are jaggy at this AMA linked stage
Transcode to DNxHD 120 50i internal RAID
Jaggy lines
#2
As above but tick Frameflex button so the vision reports as 1080 after transcode - no change, jaggy lines still
#3
Create a 1080 25p project
AMA link and transcode - jaggies are gone
Swap to 1080 50i and bring in P2 vision then
All fine too
#4
Use Adobe Media Encoder to take the 4K 50p and turn it into 1080 50i - perfect
But this adds a transcode step outside of Avid and why does Adobe's transcode engine get this right and Avid's appears broken?
Can anyone else confirm? It is a real pain.
PS monitoring on matrox/TV combo, confirmed on output DNxHD mov file export so it is not monitoring as far as I can tell - especially as it can look fine if 25p is selected at the 1080 stage..