Annotate video with frame numbers:

  ffmpeg -i input.mp4 -vf "drawtext=fontfile=font.ttf: text=%{n}: x=48: y=48: fontcolor=white: box=1: boxcolor=0x00000099: fontsize=72" -y output.mp4

Remove audio track from video:

  ffmpeg -i input.mp4 -c copy -an output.mp4