[HELP] ProRes with PCM Won't Create Output File

[Selur]

picture was a very thin letterbox - i.e. the aspect ratio was wrong.

Without a sample to reproduce it, I doubt that.
With
width: 720
height: 576
a par of 59:54
DAR is 1.36574074
like Hybrid calculated.
Only thing that might be 'wrong' is the assumed input par type (which can be change through 'Crop/Resize->Bas->Pixel Aspect Ratio (PAR)->Force input PAR type' and changes how the input PAR is interpreted).

Cu Selur