Transcoding Anamorphic 2.8K ProRes

Hello,

Today I’m going to show you a proven method to transcode 2.8K Anamorphic ProRes shot on the Alexa Mini or ARRI Amira. This particular format throws you some curveballs in the transcoding process which requires some in-depth troubleshooting. I figured out a reliable workflow to deal with this and I’ll be presenting it here in a set ready format to solve your problems when you are under the pump on location.

***If you just want the solution to the problem, please scroll down to the ‘STEPS TO TRANSCODE’ Section.***

FOOTAGE DETAILS

ACQUISITION FORMAT
File: Quicktime .mov Container
Codec: ProRes 4444 XQ
Resolution: 2880 x 2160
Project Frame Rate: 25fps
Embedded Timecode, ARRI Filenaming Convention

TRANSCODE FORMAT
File: Quicktime .mov Container
Codec: ProRes 422 Proxy
Resolution: 1920 x 1080
Project Frame Rate: 25fps
Timecode and Filename Passthrough

SOFTWARE

In this example we’ll be using DaVinci Resolve 12.5.3 for our transcode. This software can be obtain free of charge from Blackmagic Design or directly from the App Store.

LENS SQUEEZE FACTOR

In the Amira/Mini there is an option in ‘Project Settings’ called ‘Lens Squeeze Factor’, this setting is designed to provide metadata that tells your computer if the footage should be desqueezed or not. The ‘Lens Squeeze Factor’ Options are ‘1.0x’, ‘1.3x’ and ‘2.0x’. For Spherical Lenses you should leave this setting at it’s default of ‘1.0x’, in the past I have found that by setting the option to ‘2.0x’ it’ll automatically desqueeze anamorphic footage when played back in Quick Look or Quicktime. Recently I have found this is not the case, despite being set correctly on camera the metadata passthrough and implementation does not work. This should always be used as your first line of defence for dealing with Anamorphic Footage, if it doesn’t work then we deal with it in the transcode.

HOW THE FOOTAGE SHOULD LOOK

AS SHOT ON CAMERA:
This is a photo of the Alexa Mini EVF, it shows the image area within the white framelines and our recording area is everything that we see, including the shaded section. The camera sensor when in 2.8K Anamorphic Mode shoots a default aspect ratio of 2.66:1, we were framing for 2.40:1 and that is why our framelines crop the recording area on the left and right, so for post production finishing we essentially have horizontal racking room should we decide to use it.

FOOTAGE DIRECTLY AFTER OFFLOAD:
After you have wrangled the footage from the Camera CFast Card to your Hard Drives this is how the footage will appear. As you can see it’s squeezed due to shooting on Anamorphic Lenses and it is quite flat as we were recording to LogC as opposed to REC709.

INCORRECT TRANSCODE:
If you follow standard transcode procedures your footage will end up looking like this. It’s basically your desqueezed image inside of a 1920 x 1080 frame, except due to some ARRI Image Processing that occurs your footage has a black border around it. If you deliver a transcode to Post like this I can guarantee that they won’t be happy.

CORRECT TRANSCODE:
If you follow my transcode method your footage will appear as follows. It delivers full gate of your shooting format, so basically the entire 2.66:1 Image that we saw above. Most Post Houses and Editors would prefer their transcoded images that way as they have all the information and will know if there is any room to rack should a boom come into frame or if they need to use information outside of the DP’s Frame (image area) for VFX Tracking, etc.

STEPS TO TRANSCODE:

STEP 01:
Open DaVinci Resolve and Load Project. I have a default project setup specifically for on-set data/transcoding. Important Settings for Transcoding are as follows:

• Master Project Settings -> Timeline Format -> Timeline Resolution: 1920 x 1080 HD
• Master Project Settings -> Timeline Format -> Pixel Aspect Ratio: Square
• Master Project Settings -> Conform Options -> Use Timecode ‘Embedded in the Source Clip’
• Image Scaling -> Image Scaling Preset -> Mismatched Resolution Files ‘Scale Entire Image to Fit’
• Image Scaling -> Output Scaling Preset: Match Timeline Settings
• Image Scaling ->Output Scaling Preset -> Mismatched Resolution Files ‘Scale Entire Image to Fit’

STEP 02:
Make sure you are in the ‘Media Workspace’. Use the window in the top left to navigate to your camera media, select the folder containing your card, right click and ‘Add Folder and SubFolders Into Media Pool’. You should see all camera clips appear in the bottom half of the screen in your ‘Media Pool’.

STEP 03:
Select the clips that you will be transcoding from the ‘Media Pool’. You can use the Keyboard Shortcut ‘Apple + A’ to Select All. In this instance it’s just one clip so I can simply click it. Once all clips are selected, right click and select ‘Clip Attributes’.

In the ‘Clip Attributes’ Window click on the drop down next to ‘Pixel Aspect Ratio’ and select ‘Cinemascope’. In all of the DaVinci Resolve Documentation it never specifically states exactly what ‘Cinemascope’ is, but I can tell you from experience that it is a 2.0x Desqueeze which is required in this instance for our Anamorphic Footage.

Once selected, hit OK and you’ll be returned to the ‘Media Workspace’ where you can now see your footage desqueezed in the Preview Window. Please take note of the Resolution Value that we can see next to our clip in the Media Pool, it says 2944 x 2160, this will be important for solving or black border issue.

STEP 04:
Use the tabs at the bottom of the screen to change to the ‘Edit Workspace’. Here you will select all of your clips from the ‘Media Pool’ and drag them down into the ‘Timeline’. When you have dragged them in a new timeline will automatically be created called ‘Timeline 1’ which also appears in your ‘Media Pool’.

STEP 05:
In this step we are going to apply a LogC to REC709 Look Up Table so that the transcode appears as photographed on-set rather then low contrast and desaturated. Use the tabs at the bottom of the screen to change to the ‘Color Workspace’. Here you will see the clips from your ‘Timeline’ in the middle of the screen. Make sure they are all selected and right click, select ‘3D LUT -> ARRI -> ARRI Alexa LogC to Rec709’ and click. You will see your image preview increase in contrast and saturation, thus you know that it has been applied correctly.

STEP 06:
In this step we are going to amend out black border issue. For the maths behind the figures see below, here we are just going to detail how to get results.

In the lower left quadrent of the ‘Color Workspace’ you have a smaller window with many tabs such as ‘Camera Raw’, ‘Color Wheels’, ‘Window’, etc. Select your clip and then click on the ‘Sizing’ Tab.

In this tab you will have various sizing adjustments that will alter the image. The two that we are concerned with are ‘Width’ and ‘Height’. The default setting for these parameters is ‘1.000’ which means that manual resizing is not applied and the image is at it’s default proportions. As we essentially need to scale up or zoom in on the image to get rid of the black border, this is where our work will be done. Change the value of ‘1.000’ to ‘1.059’ for both ‘Width’ and ‘Height’. You will see your preview image alter and reflect a full frame 2.66:1 Image as we intended.

UPDATE:
It appears that something has changed slightly in either the way ARRI processes it’s images in the Quicktime Container or in the way that Resolve handles them, but it has been brought to my attention by a reader and also noticed by me in more recent transcodes that the 1.059 Scale on the X and Y Axis actually crops the images slightly.

Based on some new calculations and a bit of trial and error I have discovered that the new value to scale in on both X and Y should be ‘1.023’. Please follow this guide exactly as specified but rather then using the original ‘1.059’ Value, use ‘1.023’ instead.

Unfortunately when you are dealing with multiple clips in your ‘Timeline’ you won’t be able to select all and then apply the ‘Width’ and ‘Height’ adjustments as detailed above, you’ll have to do each clip individually. This is massively time consuming but fortunately there is a solution. Once you have input the appropriate values for one clip into ‘Width’ and ‘Height’ you can press the ‘Create’ Button in the top right of the ‘Sizing’ Tab. This will create a ‘Format Preset’ where we can see all of our applied sizing values. Name it something that makes sense to you and hit the ‘Save’ Button.

When dealing with multiple clips in the ‘Color Workspace’ you can select all of the clips that you need to apply the sizing transform to, then right click and select ‘Change Input Sizing Preset -> Format Preset We Created’, in my case it is called ‘2.8K_ProRes_Ana’. This will apply the preset ‘Width’ and ‘Height’ transformation to all selected clips.

STEP 07:
We are all done now with Desqueezing, LUTs and Fixing the Black Border so it’s time to actually transcode. Use the tabs at the bottom of the screen to change to the ‘Deliver Workspace’. In the top left corner is where you setup your ‘Render Settings’, thankfully Resolve makes it quite straight forward. Setup your ‘Render Settings’ as required for your specific project.

‘Render Settings’ are broken down into 3 Categories, ‘Video’, ‘Audio’ and ‘File’. I will detail my render settings below as per my transcode format at the very top of this page.

MAIN:

• Location: Desktop
• Render as ‘Individual Clips’

VIDEO:

• Video -> Export Video
• Format: Quicktime
• Codec: Apple ProRes 422 Proxy
• Leave Field Rendering Unchecked
• Resolution: 1920 x 1080 HD
• Advanced Settings: Always Check But Usually Leave at Defaults

AUDIO:

• Audio -> Export Audio
• Codec: Linear PCM
• Channels/Bit Depth: Default (2 Channels/Bit Depth 16)

FILE:

• Filename Uses ‘Source Name’
• Everything Else as Default

Once you are 100% Happy with your ‘Render Settings’, press ‘Add to Render Queue’ which will add your timeline to the ‘Render Queue’ which can be seen on the right of the screen while in the ‘Deliver Workspace’. Once it’s in there, press the ‘Start Render’ Button and away you go.

STEP 08:
Once your transcode is complete I always conduct tests to ensure all has gone as expected. I will playback the clip in Quicktime and check that it looks as expected, also listening that the sound has passed through. I will then open my original clip and my transcoded clip in Resolve and play them back from the ‘Media Workspace’, here you can check if the timecode is matching between the clips, this is displayed in the top right corner of the image preview window. I also check that the filenames match which can also be done in the image review window as seen below. Once the check and test phase is done you are good to go and the transcode is complete.

THE MATHS

In Step 03 above we briefly touched on the cause of the Black Border Issue and in Step 06 I executed a 1.059 Scale of the image to solve the issue. Now it’s time to geek out a little and explain how I obtained the magic number ‘1.059’.

THE PROBLEM:

The recording resolution of the camera is: 2880 x 2160
The resolution of the ProRes Clips straight out of camera are: 2944 x 2160

The camera resolution can be referenced by looking at the Home Screen of the Alexa Mini/Amira Menu, you can see it below where is says 2.8K ‘(2880×2160)’.

The resolution of the ProRes Clips can be checked in Resolve as we touched on before, or by simply using the ‘Get Info’ Function in macOS. Select the clip and either ‘Right Click -> Get Info’ or press ‘Apple + I’. As you can see below in the ‘More Info’ Section the Resolution or ‘Dimensions’ are referenced at ‘2944 x 2160’.

Weird right? This is basically an extra 64 Pixels on our horizontal image plane. Why you ask? ARRI details it perfectly in the Alexa Mini SUP 4.2 Release Notes:

Key words here being ‘padded with black pixels’, ‘flagged in metadata’ and ‘not all tools may respect that information’. So this basically means that the Alexa Mini/Amira adds extra black pixels around the active image area to make the ProRes Codec work with the camera, they take note of the issue via metadata but not all programs are going to use that metadata. Resolve is one of those programs and thus why we have a black border around our image.

THE MATHS:

As we discussed before, we use an image scale to solve this problem, basically blowing up the image to make the ‘recording area’ full frame and remove the ARRI induced black border. It is figured out by knowing the aspect ratios that you are dealing with and the resolutions that are being recorded, both of which we know. This was my process:

Recording Area Aspect Ratio: 2.66:1 (2.6666666667)

Resolution From Camera: 2880 x 2160
When we desqueeze this footage, which is to scale it 2.0x horizontally, it makes the resolution from camera ‘5760 x 2160’, further referenced as ‘desqueezed resolution’. The equation here is ‘(2880 x 2) x 2160 = 5760 x 2160’.

Resolution on ProRes File: 2944 x 2160
When we apply the same calculation as above to obtain the ‘desqueezed resolution’ the equation is ‘(2944 x 2) x 2160 = 5888 x 2160’.

Typically to calculate aspect ratio of an image you divide the horizontal resolution by the vertical resolution, for Full HD that would be ‘1920 ÷ 1080 = 1.7777777778’. When you round this to simplified form you get 1.78, which is referencing our common 1.78:1 Aspect Ratio, commonly known as 16:9.

We apply a similar calculation to our ‘desqueezed resolutions’ above.
Desqueezed Camera Resolution: 5760 ÷ 2160 = 2.6666666667
Desqueezed ProRes File Resolution: 5888 ÷ 2160 = 2.7259259259

This indicates that our ‘Desqueezed Camera Resolution’ has a 2.66:1 Aspect Ratio which is as intended, but our ‘Desqueezed ProRes File Resolution’ has a 2.73:1 Aspect Ratio which is not what we were shooting.

So basically my next step was to find out the difference between the two aspect ratios which was done by subtracting the ‘Camera Aspect Ratio’ from the ‘ProRes File Aspect Ratio’ which is as follows: ‘2.7259259259 – 2.6666666667 = 0.0592592592’.

This tells us that the difference between the ‘actual resolution’ and the ‘intended resolution’ is ‘0.0592592592’. Meaning that we need to scale our image by that value to remove the black border. As you can remember, Resolve sees our default image scale as 1.000, so in order to apply that scale we add our value above to 1.000: ‘1.000 + 0.0592592592 = 1.0592592592’.

As Resolve works to 3 Decimal Places for ‘Sizing Input’ we need to round that number to work with Resolve which would turn ‘1.0592592592’ to ‘1.059’. You then input that ‘1.059’ Value into our ‘Width’ and ‘Height’ fields and viola, we have our solution as well as our process in figuring out that magic number.

UPDATE:
While maths is all good and well in solving many of the problems that we face in life, sometimes it just doesn’t work. While initially when I first tackled this transcoding problem a scale of ‘1.059’ on the X and Y worked perfectly to correct the black border, now it doesn’t. So please in future iterations of completing this transcode task please use the value of ‘1.023’ on the X and Y Scale to ensure you have a full frame anamorphic image with no cropping.

CONCLUSION

I hope you have found this transcoding and problem solving tutorial helpful. My best intention is that it gets you out of a tricky and time consuming mathematical exercise on-set when the DP wants to shoot 2.8K Anamorphic ProRes and the PM asks you to provide transcodes for Post Production with very little notice as has happened to me in the past. If you’ve got any question or queries, feel free to hit me up in the comments below.

 

Thanks!

 

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