I can open .mov files. The only thing I changed in your script was the hevc_nvenc option in ffmpeg because it uses the nvidia encoder when creating the hardsub video. In the first line I changed hevc_nvenc to libx264.
Thank you for your hardsubs and the script, I ended up modifying it because I don't have a nvidia gpu
ffmpeg -loop 1 -i "FILENAME.jpg" -i "FILENAME.mp3" -c:v libx264 -vf
"scale=1920:1080:force_original_aspect_ratio=decrease,pad=1920:1080:-1:-...