Update day-1.md

Author: hwulet

day-1.md

@@ -5,3 +5,8 @@
 - [ ] Convert my first blog post into an actual webpage.
 
 ## Review
+Convert an image or video from dark mode to light mode using [ffmpeg](https://www.ffmpeg.org)
+
+```bash
+ffmpeg -i input.mp4 -vf "negate,hue=h=180,eq=contrast=1.2:saturation=1.1" output.mp4
+```