I have been beating on this a bit for the last few days.  Mainly on the SD to HD side of the problem.
Here is what I have learned.

First - read Chapter 10 of the latest Resolve 17 manual.  All of it.  Then read it again. 

Now - when Avid sees a clip whose raster size does not match the raster size of your sequence it immediately adds a FrameFlex adapter and scales the non raster matching clip to the sequence raster via either Fit or Fill depending on how you set up FrameFlex in the Source settings.  It then normalizes the scale number to 100.  This is important to keep in mind.  (And the root of the problem.)

One note. Thanks to oklaroma we now know that you need to add a key frame to the actual FrameFlex clip effect to “set” the numbers so that they will transfer to Resolve via AAF.  This seems to be a good idea even if you just want to leave it at the default scale.

Now for my experiments (SD to HD) I had the Resolve project default input sizing set to Center Crop No Resize.  This means that SD clips will show up as postage stamps in Resolve.  This is because of Avid normalize step.  Avid does not seem to be publishing the initial scale that Resolve is doing in any manner.  Resolve sees a scale of 100 and says ok.  Done.  

Now you need to add the missing first step that Avid did (and hid). After this the scaling and positioning info you put into the FrameFlex clip effects should then take effect  I did this by going to the Inspector of such a clip in the Edit page and going to Input Scaling near the bottom and changing that from Project Default to either Fit or Fill depending on whether I had set 4x3 or 16x9 as my Image size in FrameFlex.  This is in essence the first thing Avid does but hides from the AAF.

According to the Resolve manual that you read earlier, Resolve seems to be concantenating the two sizing maths into only one scaling action.  Great.  It seems you can select multiple clips using various tools in Resolve and make the modifications to a group of clips at one time (Hello Avid).

Exactly how this is applied to UHD too HD I have not tried yet.  But I believe it will be related.  Hope this makes sense and helps someone. 

jef:

Now for my experiments (SD to HD) I had the Resolve project default input sizing set to Center Crop No Resize.

Thanks for the detailed information Jef - there's one positive adantage of working in this way and having resolve ignore Avid's upscaling resize, and that is the upscaling in Resolve is so much better than Avid. Particularly SD to HD. I have one such project that I am remastering to HD and this is my workflow. Of course if all the pips have to be converted to 3D warp though.

N Ryan:

I did some tests sending Avid AAFs to Resolve (the first half of roundtripping) just to get my head around the difference for Resolve of receiving sizing information from FrameFlex versus a filter (3DWarp etc.)

I got a UHD clip and cut it into a HD Sequence (common formatting for me) multiple times. There was no Frameflex action in the source clp.

I then applied different resizing methods to obtain the same effect. Static, no moves.

Here's what went across, successfully:

clip 1: Frameflex with one keyframe

clip 2: Frameflex with no keyframes

clip 3: 3DWarp

clip 4: Resize

clip 5: which was a HD clip with a Resize

What doesn't go across of course, is combinations - they become like Nested Effects, which are not supported. So using Frameflex + 3DWarp or Frameflex + Resize does not combine the sizing attributes into one for Resolve. In both these cases, the Frameflex numbers went through and the 3DWarp or Resize was excluded.

So, just to reiterate, RESIZE works for me.

MC 2021.9      DaVinci Resolve 17.2.1

 

Many thanks for this. 

Adding keyframes to clips in Avid with Frameflex applied also worked for me.

WORKFLOW: UHD camera footage brought into Resolve; made UHD proxies for editing in Avid; edited in 1080 timeline in Avid using UHD proxies with Frameflex applied to all shots for various crops, etc. Added a keyframe as per suggestion, to the first frame of each shot (took too long - please fix this Blackmagic), then created AAF link that was imported into Resolve. All shots display with correct sizing now in Resolve.

Before using this keyframe technique, shots with Frameflex applied showed up as only Cropped in Resolve with black borders. Shots were not actually resized at all, just cropped. 

Although the keyframe method took time, it was far faster than resizing each shot manually in resolve. Thank you for this workaround! 

pcr:

Although the keyframe method took time, it was far faster than resizing each shot manually in resolve. Thank you for this workaround! 

What happens if your timeline frameflex clip uses two keyframes ? Does a frameflex Pan & Zoom effect translate?

I believe it respects the Keyframed movement but I will give it a test and report back.