Adjusting Draw Text Scrolling Length in FFmpeg Text File
When creating videos using the FFmpeg tool, you may need to add text to the video. The drawtext filter in FFmpeg allows you to add text to your video, and you can make the text scroll vertically by using the y option. However, you may want to adjust the scrolling length of the text based on the length of the text in the input text file.
The drawtext Filter
The drawtext filter in FFmpeg is used to add text to a video. The basic syntax for using the filter is as follows:
ffmpeg -i input.mp4 -vf "drawtext=fontfile=/path/to/font.ttf: \
text='%{filename}': fontcolor=white: fontsize=24: box=1: [email protected]: \
boxborderw=5: x=(w-text_w)/2: y=h-(2*lh)" output.mp4In this example, the drawtext filter is used to add the filename of the input video to the video as text. The text is centered horizontally (x=(w-text_w)/2) and positioned near the bottom of the video (y=h-(2*lh)).
Scrolling Text
To make the text scroll vertically, you can use the y option in the drawtext filter. For example, the following command will make the text scroll vertically from the bottom of the video to the top:
ffmpeg -i input.mp4 -vf "drawtext=fontfile=/path/to/font.ttf: \
text='%{filename}': fontcolor=white: fontsize=24: box=1: [email protected]: \
boxborderw=5: x=(w-text_w)/2: y=h-2*lh-t*n: fontfile=/path/to/font.ttf" \
-c:v libx264 -crf 23 -t 10 output.mp4In this example, the y option is set to y=h-2*lh-t*n, where t is the duration of each frame (in seconds) and n is the frame number. This will make the text scroll vertically from the bottom of the video to the top at a rate of one character per frame.
Adjusting Scrolling Length
To adjust the scrolling length of the text based on the length of the text in the input text file, you can use the read_file filter to read the contents of the text file and pass it to the drawtext filter. For example, the following command will read the contents of the text.txt file and make the text scroll vertically from the bottom of the video to the top:
ffmpeg -i input.mp4 -vf "read_file='text.txt':fps=1, \
drawtext=fontfile=/path/to/font.ttf: text='%{filename}': fontcolor=white: \
fontsize=24: box=1: [email protected]: boxborderw=5: x=(w-text_w)/2: \
y=h-2*lh-t\*n: fontfile=/path/to/font.ttf" \
-c:v libx264 -crf 23 -t 10 output.mp4In this example, the read_file filter is used to read the contents of the text.txt file at a frame rate of 1 frame per second. The output of the read_file filter is then passed to the drawtext filter, which makes the text scroll vertically from the bottom of the video to the top.
In this article, we have covered the basics of using the drawtext filter in FFmpeg to add text to a video and make the text scroll vertically. We have also shown how to adjust the scrolling length of the text based on the length of the text in the input text file using the read_file filter.