The idea of having a box with text is to use the FFmpeg filter i.e
-vf "drawtext=fontfile=Arial.ttf: text='%{frame_num}': start_number=1: x=(w-tw)/2: y=h-(2*lh): fontcolor=black: fontsize=20: box=1: boxcolor=white: boxborderw=5"
drawtext
- fontfile: The font file to be used for drawing text. The path must be included. This parameter is mandatory if the fontconfig support is disabled.
- text: The text string to be drawn. The text must be a sequence of UTF-8 encoded characters. This parameter is mandatory if no file is specified with the parameter textfile.
- x,y: The expressions which specify the offsets where text will be drawn within the video frame. They are relative to the top/left border of the output image. The default value of x and y is "0".
- fontcolor: The color to be used for drawing fonts. For the syntax of this option, check the (ffmpeg-utils)"Color" section in the ffmpeg-utils manual. The default value of fontcolor is "black".
- fontsize: The font size to be used for drawing text. The default value of fontsize is 16.
- box: Used to draw a box around text using the background color. The value must be either 1 (enable) or 0 (disable). The default value of box is 0.
- boxcolor: The color to be used for drawing box around text. For the syntax of this option, check the (ffmpeg-utils)"Color" section in the ffmpeg-utils manual. The default value of boxcolor is "white".
- boxborderw: Set the width of the border to be drawn around the text using bordercolor. The default value of borderw is 0