Working with Alexa Mini 4K UHD clips

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Esteban Wiaggio

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  • Joined: Thu Mar 28, 2013 5:47 pm
  • Location: Spain

Working with Alexa Mini 4K UHD clips

PostSun Feb 09, 2020 1:30 pm

Hi
For the first time in ages, I had to shoot in ProRes 4444 4K UHD with a Mini.
No way to convince the client that the camera upscales the output from the sensor.
I Ingested the clips in Resolve 16.1.2
I created a timeline with HD format.
When I play back a clip, the viewer zooms in so I can see just a portion of the clip.
So I checked if the monitoring settings were set to 'center crop' or something similar.
They're set to 'match timeline settings' and to 'scale entire image to fit'.
The input scaling has that same value.
Everything looks as it should.
I tested one of the clips in another computer with the same Resolve version and the behaviour is the same. It zooms in when playing back.
I then ingested one of this clips into another project shot with Alexa LF Open Gate, where I can play back the clips with even larger frame, with no zoom in.
I created an empty timeline in HD size, added an LF Open Gate clip and a Mini 4K UHD clip.
The LF clip plays back fine and the alexa Mini 4K UHD one zooms in.
So I guess there's something in the 4K UHD metadata that's causing Resolve to 'think' that it should play back applying a zoom in, overriding what's specified in the image scaling parameters.
In the edit page, if I use an edit tool, the viewer shows the right sized frame when cutting or extending the clip.
The only way i've found is to to play back the actual frame by keeping pressed the right arrow key.
If I scrub the playhead i get a mixture of real frame + zoomed frame.
I made a comparison between the actual frame and the zoomed playback, and it's exactly zoomed in 2x.

Exporting the clips using individual names / source clip name, and using HD as the output format works as expected.
Exporitng the timeline in HD format works as expected as well.
It seems to be only a preview issue during playback, with footage shot in that format.

A few frame grabs and a demo clip are available if needed.
Cheers
Last edited by Esteban Wiaggio on Sun Feb 09, 2020 2:01 pm, edited 1 time in total.
Esteban Wiaggio
Digital Image Technician / Onset Colorist / Onset Editor
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John Paines

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Re: Working with Alexa Mini 4K UHD clips

PostSun Feb 09, 2020 1:59 pm

It's a known bug, with Alexa prores. This workaround was offered:

"Top Menu 'DaVinci Resolve' -> Preferences -> 'User' tab -> Playback Settings -> Set 'Performance Mode' to manual -> un-check 'Optimized Decode Quality'
You don't need to restart Resolve for this to take effect."
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Esteban Wiaggio

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  • Location: Spain

Re: Working with Alexa Mini 4K UHD clips

PostSun Feb 09, 2020 2:03 pm

It works.
Thanks very much !

Cheers
Esteban Wiaggio
Digital Image Technician / Onset Colorist / Onset Editor
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MarcusTimpson

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Re: Working with Alexa Mini 4K UHD clips

PostWed Feb 12, 2020 9:10 pm

Nice that there is at least a work around, but does anyone know if this will be addressed?
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hartogcolor

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  • Location: Oakland
  • Real Name: Lucas Hartog

Re: Working with Alexa Mini 4K UHD clips

PostTue Feb 25, 2020 12:28 am

Thanks for figuring this out ! This has been major source of irritation lately . I hope an update fixes this realtively new issue.

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