Log file can be found in the voukoder tray icon now.

You have to open the voukoder settings window, then the icon should appear.

Your card does not support encoding HEVC:

Source

Vouk's right about height divisible by 8 requirement (and width divisible by 16). It has to do with macroblocks & compression.

You might get away with resolution that doesn't adhere to these requirements, but it's a bit of a lottery.

Depending on the codec, format and how Youtube's ffmpeg-based encoder processes it, it might end up with a green line too.

I've bumped into this issue myself a couple years back with Cineform codec, which requires width/16 & height/8 rule otherwise it gets that bottom line when played back in anything but Adobe.

3840x1600 is a good choice, it's 2.40:1 which is pretty much the same as 2.39:1 cinemascope (which is just a legacy of analog film/projection era)

21:9 is just a marketing number used for monitors and phones. The existing ultra wide resolutions in things like consumer monitors aren't exactly 21:9 and they still adhere to the rule, like 2560x1080 (2.37:1), 3440x1440 (~2.39:1) and 3840x1600 (2.40:1)

In cinema mastering / intermediate , they don't have to care about conforming to standard resolutions because it's exported as separate frames.

But when delivering, they adjust it to meet requirements.