Single source
ffmpeg.exe -i "input with spaces.mkv" -map 0:0 -map 0:1 \
-c:a eac3 -ab 128k -ac 2 \
-c:v libx264 -preset:v veryfast -tune:v animation -profile:v high -level:v 4.1 -b:v 3000k -strict -2 \
-x264-params ref=4:subme=8:me_range=16:trellis=1:threads=18:lookahead_threads=3:bframes=3:keyint=240:keyint_min=24:rc_lookahead=50:ratetol=1.0:cplxblur=20.0:qblur=0.5 \
-vf "subtitles='input with spaces.mkv':si=0:force_style='Outline=1,Shadow=0'" output.mp4