Black fontcolor being transparent in drawtext in ffmpeg
The method in my old answer was a workaround due to a limitation in drawtext filter at the time of writing. It's easier now.
You're getting transparent text because the textcolor is used to set both the color as well as its opacity intensity, and since black represents 0, the text disappears.
Anyway, it's simpler after ffmpeg 3.1
ffmpeg -i input.mp4 -filter_complex &quot;color=black@0:100x100,format=yuva420p[c];[c][0]scale2ref[ct][mv];[ct]setsar=1,drawtext=fontfile='font.ttf':text='Test Text':fontsize=36:line_spacing=3:box=1:boxcolor=red@1:fontcolor=black,rotate=45:ow=rotw(45):oh=roth(45):c=black@0[txta];[mv][txta]overlay=x='min(0,-H*sin(45))+100':y='min(0,W*sin(45))+50':shortest=1&quot; output_video.mp4