ffmpeg subtitles alignment and position

Turns out the trick for doing this is to add Alignment=0. Then you can use MarginV and MarginL freely:

ffmpeg -i "imput.mp4" -lavfi "subtitles=subtitles.srt:force_style='Alignment=0,OutlineColour=&H100000000,BorderStyle=3,Outline=1,Shadow=0,Fontsize=18,MarginL=5,MarginV=25'" -crf 1 -c:a copy "output.mp4"