问题
The test command I have is as follows:
ffmpeg -i in.mov -vf "drawtext=fontfile=/usr/share/fonts/ttf-bitstream-vera/Vera.ttf: x=(w-tw)/2: y=h-(2*lh)-n: fontcolor=white: fontsize=40: box=1: boxcolor=0x00000000@1: text=" -an -y out.mov
I want to display the frame number on each frame. However, setting the "text" variable to "n" does not help (it displays n) and %n seems to be the new line symbol. The thing that confuses me most is that this part
y=h-(2*lh)-n
works well, meaning it gets the right value of the current frame and moves the text up accordingly.
回答1:
Ok, this feature was not there in ffmpeg, but now it is. And this is how you do it:
...drawtext=text=%{n}:expansion=normal:fontfile=/usr/share/fonts/ttf-bitstream-vera/Vera.ttf:other_options...
Note that expansion should be set to normal, which is not the default now, but should be default in the future (according to the ffmpeg documentation).
来源：https://stackoverflow.com/questions/13494902/how-to-display-a-frame-number-on-each-frame-of-a-video-using-ffmpeg