I have found out how ffmpeg can add image watermark at the bottom left of a video
ffmpeg -i "C:\test.mp4" -i "C:\test\watermark.png" -filter_complex "overlay=10:main_h-overlay_h-10" "C:\test-watermark.mp4"
but I am looking for a way to add text (white, 12px text, with black shadow to make the text readable) instead of an image. Can somebody help me?