Firefox Video Preloading
ffmpeg -i original.mp4 -s 1280x720 -t 5 -an -c:v libx264 -b:v 2000k -pass 1 -f null NUL && ffmpeg -i original.mp4 -s 1280x720 -t 5 -an -c:v libx264 -b:v 2000k -pass 2 h264.mp4
ffmpeg -i original.mp4 -s 1280x720 -t 5 -an -c:v libx264 -b:v 2000k -pass 1 -f null NUL && ffmpeg -i original.mp4 -s 1280x720 -t 5 -an -c:v libx264 -b:v 2000k -pass 2 h264.mp4