[FFmpeg-user] How add expression in drawtext's text

[qw]

Hi,


I can use the following command to add frame number on video:


/usr/local/bin/ffmpeg -t 180 -i input.mp4 -acodec libfdk_aac -ac 2 -b:a 48k -vcodec libx264 -b:v 500k -g 25 \
-vf "fps=fps=25, scale=w=320:h=240, drawtext='box=1:fontcolor=red:fontsize=20:fontfile=OpenSans-Regular.ttf:text=%{frame_num}'" \
-f mp4 out.mp4


But the width of the text box will increase as frame number increases. I want to make the width of the text box unchanged. If the largest frame number is 99999, I want to make the width of the text is of 5 numbers. How to do it?




Another question:


I want to make the following logic for text:


if frame number < 10
    text=0000%{frame_num}
else if frame number < 100
    text=000%{frame_num}
else if frame number < 1000
    text=00%{frame_num}
else if frame number < 10000
    text=0%{frame_num}
else
    text=%{frame_num}


How to do it? How can I add expression in text? Is there any command example?


Thanks

regards

andrew