How to add a fade in within overlay with FFMPEG ?

Question

I'm wondering how to add the option "fade in" in the -filter_complex 'overlay'.

The basic overlay

ffmpeg -i movie.mp4 -i image.jpg -c:v libx264 -filter_complex 'overlay=x=main_w-overlay_w-100:y=main_h-overlay_h-100' output.mp4

Does the image.jpg fade=in should be in filter_complex like this ?

ffmpeg -i movie.mp4 -i image.jpg -c:v libx264 -filter_complex 'fade=in:st=0:d=5:alpha=1, overlay=x=main_w-overlay_w-100:y=main_h-overlay_h-100' output.mp4

Thanks a lot for your help on the construction of the -filter_complex parameter !

Answer 1

Use

ffmpeg -i movie.mp4 -loop 1 -i image.jpg -filter_complex
      "[1]format=yuva420p,fade=in:st=0:d=5:alpha=1[i];
       [0][i]overlay=W-w-100:H-h-100:shortest=1"
-c:v libx264 output.mp4

Your fade filter is set to operate on the alpha channel, but JPEGs don't have alpha, so the image needs to be converted to a pixel format that does. Also, FFmpeg is a time-based processor of streams and a single image is treated as one frame at 25 fps, thus lasting 0.04 s, so I added a loop to generate a video stream out of it, which is needed for the fade to take effect.

The overlay filter takes in two inputs, so I assigned all the pads for explicit routing. Since the image is looped indefinitely, the shortest is added to stop the overlay when the main video ends.