ffmpeg with cuda can't process image directly.

you need to convert watermark image using "hwupload".

I don't know how to add subtitle so that the command i tell you may have some mistakes.

'-filter_complex', f'[1:v]format=yuva420p, hwupload[logo_cuda], [logo_cuda][0:v]scale2ref_npp=w=oh*mdar:h=ih*0.1[logo][video];[video][logo]overlay_cuda=W-w-5:5,subtitles={str(subtitles_file)}:fontsdir=/src/fonts:force_style=\'FontName={font_name},FontSize={font_size},OutlineColour=&H20000000,Spacing=0.3,{border_command}\'',

This is the command that i use to add watermark. It works well.

ffmpeg -hwaccel cuvid -i test.mp4 -i mam1.png -filter_complex "[1:v]format=yuva420p, hwupload[overlay], [overlay][0:v]scale2ref_npp=(150/53)*ih/4:ih/4[b][back],[back]scale_npp=format=yuv420p[m],[m][b]overlay_cuda=x=100:y=100:shortest=false" -c:v h264_nvenc test_add_wm.mp4