Overlay timelapse video on solid background colour using ffmpeg

You can use the color filter as a background:

ffmpeg -f lavfi -i color=c=white:s=1920x1080:r=24 -framerate 24 -i input_%04d.png -filter_complex "[0:v][1:v]overlay=shortest=1,format=yuv420p[out]" -map "[out]" output.mp4

Also see:

• image demuxer documentation
• overlay filter documentation
• How to position overlay with ffmpeg?