Creating video containing animated text using FFMPEG alone

Question

I doubt this is possible, but am trying to find some way to

1. dynamically render text, and then
2. optionally animate it (simple left to right movement) and then
3. composite the result on top of another video.

I know FFMPEG is powerful, but is it possible to generate content dynamically like this using FFMPEG alone? The video would be input, but the text would have to be generated entirely using FFMPEG.

Answer 1

You can use the drawtext filter.

Dynamic text

The text can be changed during encoding if you use textfile and reload options:

• textfile A text file containing text to be drawn. The text must be a sequence of UTF-8 encoded characters.

• reload If set to 1, the textfile will be reloaded before each frame. Be sure to update it atomically, or it may be read partially, or even fail.

Animate

The text can move around using expressions within the x and y drawtext options. See the drawtext documentation for a list of constants and functions.

Timeline editing

Some filters, such as drawtext, support the enable option meaning you can turn the filter off and on. You can see what filters support timeline with:

ffmpeg -filters

Example

If you have an input video that you want to overlay with text:

ffmpeg -i input -vf "drawtext=enable='gte(t,3)':fontfile=Vera.ttf:textfile=text.txt:reload=1:y=h-line_h-10:x=(W/tw)*n" output

• This will enable the drawtext filter after 3 seconds
• Every time text.txt is updated the text will change
• The words will move on the screen from the left to the right (I suck at these expressions but you'll get the idea)

If you have no input video and would just like to generate the text on black background:

ffmpeg -f lavfi -i "color=color=black, drawtext=enable='gte(t,3)':fontfile=Vera.ttf:fontcolor=white:textfile=text.txt:reload=1:y=h-line_h-10:x=(W/tw)*n" -t 5 output

Here, -t 5 specifies the overall length of the output. (If not specified, the encoding would run forever.) The font color is set to white so the text becomes visible.