rawshooter

ffmpeg is multiplatform and only uses its own, included codec library (here is a complete list of all encoders). Performance is practically the same on Windows, Linux and MacOS, although the program is chiefly developed under Linux.
Hardware acceleration indeed degrades the export quality to h.264 or h.265 if you use the (very fast) on-chip encoders of Nvidia and AMD GPUs. The CPU-only x264 and x265 codecs of ffmpeg yield much better image quality, especially if you use the "slow" or "very slow" encoding preset and the "film" tuning parameter. (They are also available in the Handbrake GUI.) You pay with much longer encoding time. Optionally/alternatively, ffmpeg can also use the Nvidia on-chip encoder (nvenc, which you can select in Handbrake as well).
For me, as a commandline person, it's easier to just type "ffmpeg -i myvideo.mxf -vcodec libx264 -b:v 18000k -tune film -preset veryslow -b:a 192k myvideo.mp4" than clicking through Handbrake's menus, but your mileage may vary... 

In the end, all the free/Open Source conversion programs - including Handbrake and Staxrip - are just graphical user interfaces for ffmpeg, and will thus yield the same results and performance. So one can simply stick with the tool whose user interface one prefers - or use ffmpeg directly on the command line. (Which provides more advanced functions such as ProRes and DNxHR encoding...)

In the end, all the free/Open Source conversion programs - including Handbrake and Staxrip - are just graphical user interfaces for ffmpeg, and will thus yield the same results and performance. So one can simply stick with the tool whose user interface one prefers - or use ffmpeg directly on the command line. (Which provides more advanced functions such as ProRes and DNxHR encoding...)

@Andrew Reid, maybe what has been noted in this collaborative Google sheet should be included in your bug report to Sigma:
https://docs.google.com/spreadsheets/d/1FUt1bfhWYftUhlABkO91goSNEYuPZzlrxmOVGDJnQ7E/edit?usp=sharing
 
general (both stills & video)
Touch screen to move zoom centre Touch for QS video specific
audio level adjustment is deeply buried in a submenu audio levels cannot be set to a low level RAW clipping indicators 12bit linear RAW at 25p 12bit as 10bit + curve 24fps not supported DCI aspect ratios not supported Black level changes during recording at certain ISOs on firmware 1.01 support USB Audio DAC video recording unresponsive after using UVC still photo specific
exposure compensation not easily available in M mode no DOF preview. lens always preview and focus at wide open. Manual focus exposure preview is not correct Magnifier location select with touch 2 - Feature requests
Operation
allow af-on button when in manual focus mode allow 2 second timer for movies. To disable shake at the beginning of the shot when on tripod allow manual focus override when in autofocus mode allow change of focus direction linear mode for focussing Ability to assign functions to left and right side of function wheel. Allow the record button to be used for custom functions Display
magnify during movie recording magnify time after touching lens 0.5 seconds zebra and focus peaking at the same time Proper RAW histogram option, like RED cameras have Ability to vertically flip the screen, for use with a mirror to shoot twin-lens reflex camera-style. Color
LUT support / bake LUT in-camera Recording formats:
10 bit non linear raw internal 10 bit non linear raw external 12 bit raw at 25 frames per second lossless compressed raw 10 bit MOV recording, HEVC True 24 frames per sesond option

With 44 x 33 mm sensor size, Fuji's GFX "medium format" is, in reality, more a plus-size full frame 35mm (36x24mm) format than what is known as medium format in film photography  (60x90mm, 60x70mm, 60x45mm - i.e. twice to four times the sensor size of GFX).

So arguably, they already have full frame, but only smartly market it as medium format. 

With 44 x 33 mm sensor size, Fuji's GFX "medium format" is, in reality, more a plus-size full frame 35mm (36x24mm) format than what is known as medium format in film photography  (60x90mm, 60x70mm, 60x45mm - i.e. twice to four times the sensor size of GFX).

So arguably, they already have full frame, but only smartly market it as medium format. 

"camera: EOS-M with MagicLantern, lens: Angenieux 8-64mm Super 8 zoom, recording format: MagicLantern 14bit raw" :
 

"camera: EOS-M with MagicLantern, lens: Angenieux 8-64mm Super 8 zoom, recording format: MagicLantern 14bit raw" :
 

I can also warmly recommend the Tokina 28-70mm/2.8 which is a bought-up and continued Angenieux design:
https://cameragx.com/2018/04/11/the-truth-about-the-angenieux-28-70-af-zoom/

I can also warmly recommend the Tokina 28-70mm/2.8 which is a bought-up and continued Angenieux design:
https://cameragx.com/2018/04/11/the-truth-about-the-angenieux-28-70-af-zoom/

I can also warmly recommend the Tokina 28-70mm/2.8 which is a bought-up and continued Angenieux design:
https://cameragx.com/2018/04/11/the-truth-about-the-angenieux-28-70-af-zoom/

Actually not... ? When the Sigma fp records CinemaDNG, it doesn't debayer the image, since a raw image is undebayered. But at the same time, I doesn't record the actual raw sensor image, but downscales the 6K undebayered sensor data to a 4K undebayered image - whose pixels no longer correspond to the sensor pixels and are a fake sensor pattern. 
Or, in less abstract language: the camera downscales the 6K raw sensor data into simulated raw sensor data of a virtual, software-made 4K sensor. Which creates all kinds of weird artifacts, as demonstrated above in the visual comparisons of the camera's 6K stills with the camera's 4K video.

The Super 16 crop mode on the Pocket 4K is IMHO superior to the original Pocket, because it is in 2.7K which yields very clean downsampled 2K/1080p, as opposed to the moiré-plagued and IR pollution-prone image of the original Pocket, and because of the camera's dual gain sensor and dramatically better low light performance.
Plus better codec (IMHO), much better battery life and much better display.

So I just did that - but I had no resolution chart at hand, but used a fine-pattern silver synthetic fabric to provoke moiré in the camera. 
With the Sigma 45mm/2.8, I did two shots, both at f8 and 11 degree shutter:
- one UltraHD CinemaDNG shot;
- one 24MP still DNG shot.
I processed both in RawTherapee (but without False Color suppression filter):

6K (24MP) still DNG

4K (12MP) CinemaDNG

The difference becomes already visible here, but for 1:1 comparison, I opened the 24MP still in The Gimp, scaled it to 3840 horizontal pixel (using cubic scale) and cropped it from 3:2 to 16:9 aspect ratio:

still DNG, scaled & cropped to 4K 3840x2160

Now let's compare the 4K still DNG and the 4K CinemaDNG in a 1:1 center crop:

CinemaDNG

still DNG, downsampled to 4K
 
While there's visible moiré also on the still DNG, the result in 4K CinemaDNG is much worse, very obviously because of a problematic scaling method. (Scaling an undebayered 6K/24MP Bayer matrix into an undebayerd 4K/12MP Bayer matrix, and probably not using the best algorithm for that.) 
The result is both an excessive pronunciation of moiré and (compared to the downscaled 6K) a blurry image - much like in the good' old Canon video DSLR times... 
 
 
One more test:

center crop from the still DNG, this time downscaled in the Gimp from 6K to 4K without any pixel downsampling, but with line skipping ("Interpolation off") -


still DNG, line-skipped from 6K to 4K
 
Moiré is more pronounced than in the downsampled still, but still not as bad as in the CinemaDNG. So I really suspect the culprit in the transformation of the undebayered 6K to undebayered 4K, probably through crude line skipping/heuristics.
 

Just to make the matter less abstract, the problem of scaling a 6K Bayer pattern into a 4K Bayer pattern is that this...

...needs to be turned into this:

Which is only possible with weird interpolations.
Or, on a larger scale, if you have 3x3 of the above four pixel groups....

....how to scale them into 2x2:

However you do it, it will result in weirdness, since you're not actually interpolating adjacent color values (as you would do in an undebayered image).
 
 

I processed the first frame with Resolve and with Rawtherapee (which includes very fine-grained, expert debayering controls). When tuning the debayering in Rawtherapee, choosing AMaZE as the demosaicing algorithm with 'border' set to 4 and 'False color suppression steps' set to 5, the result is visibly better than from Resolve, but still far from perfect - see the attached frame grabs:
 

Rawtherapee
 

Resolve

The A7iii is a good allround video camera and really excellent stills camera (I do own it), but no cinema camera because of its weak codecs and 8bit limitation, no matter how you rig it up.

The German video site Slashcam just ran a new test for using run-of-the-mill SATA SSDs in USB 3.1 enclosures as recording media with the fp:
https://www.slashcam.de/artikel/Kurztest/slashCHECK---Nachgereicht---Guenstige-SATA-SSDs-an-der-Sigma-fp-Teil-2.html

A test they had conducted earlier did fail, but it turns out that you need an enclosure that supports  USB-C 3.1 Gen 2 with, most importantly, the USAP protocol (USB Attached SCSI Protocol). The enclosure they tested, and which meets these standards, is the UGREEN 2.5" USB-C 3.1 Gen 2:

Turns out that an older Sandisk SanDisk Ultra II 960GB, while performing slightly worse in that housing than the Samsung T5, recorded 4K RAW with the Sigma fp without any trouble or disruption.  
So this might be a budget tip for the camera.
 
 

In practice, you can switch forth and back between full frame 4K raw and APS-C 4K raw video recording without great image quality penalty. (The difference in noise and resolution is IMHO invisible if you master in 1080p). And you can put the full frame vs. APS-C crop switch on the camera's quick access menu.
That effectively turns any prime lens into a dual-focal length lens - or virtual dual lens turret. Often, this makes a zoom lens unnecessary in the field.
It's a neat (and often overlooked) little feature of the camera.

In practice, you can switch forth and back between full frame 4K raw and APS-C 4K raw video recording without great image quality penalty. (The difference in noise and resolution is IMHO invisible if you master in 1080p). And you can put the full frame vs. APS-C crop switch on the camera's quick access menu.
That effectively turns any prime lens into a dual-focal length lens - or virtual dual lens turret. Often, this makes a zoom lens unnecessary in the field.
It's a neat (and often overlooked) little feature of the camera.

If your target is h264/h265, Handbrake is not only free and Open Source, but also achieves better image quality than Adobe Media Encoder. 

In practice, you can switch forth and back between full frame 4K raw and APS-C 4K raw video recording without great image quality penalty. (The difference in noise and resolution is IMHO invisible if you master in 1080p). And you can put the full frame vs. APS-C crop switch on the camera's quick access menu.
That effectively turns any prime lens into a dual-focal length lens - or virtual dual lens turret. Often, this makes a zoom lens unnecessary in the field.
It's a neat (and often overlooked) little feature of the camera.

If you consider using the lens on a Blackmagic Camera or another MFT camera that shoots raw video, go for the Voigtlander, because it's an optically corrected wide-angle lens while the PanaLeica 12mm has strong native fisheye distortion that gets electronically corrected (=photoshopped in firmware) in Panasonic and Olympus MFT cameras.
This is how the uncorrected image of the PanaLeica 12mm looks:

After in-camera software correction (only on Panasonic and Olympus bodies, not on Blackmagic):

Source: 
https://www.lenstip.com/505.6-Lens_review-Panasonic_Leica_DG_Summilux_12_mm_f_1.4_ASPH_Distortion.html
 
 

If you consider using the lens on a Blackmagic Camera or another MFT camera that shoots raw video, go for the Voigtlander, because it's an optically corrected wide-angle lens while the PanaLeica 12mm has strong native fisheye distortion that gets electronically corrected (=photoshopped in firmware) in Panasonic and Olympus MFT cameras.
This is how the uncorrected image of the PanaLeica 12mm looks:

After in-camera software correction (only on Panasonic and Olympus bodies, not on Blackmagic):

Source: 
https://www.lenstip.com/505.6-Lens_review-Panasonic_Leica_DG_Summilux_12_mm_f_1.4_ASPH_Distortion.html
 
 

If you consider using the lens on a Blackmagic Camera or another MFT camera that shoots raw video, go for the Voigtlander, because it's an optically corrected wide-angle lens while the PanaLeica 12mm has strong native fisheye distortion that gets electronically corrected (=photoshopped in firmware) in Panasonic and Olympus MFT cameras.
This is how the uncorrected image of the PanaLeica 12mm looks:

After in-camera software correction (only on Panasonic and Olympus bodies, not on Blackmagic):

Source: 
https://www.lenstip.com/505.6-Lens_review-Panasonic_Leica_DG_Summilux_12_mm_f_1.4_ASPH_Distortion.html