How to apply a watermark without quality loss?

Question

Video

How to apply a watermark through FFmpeg without quality loss?
MP4 format, convecting back and forth is not an option.

Answer 1

Short answer: no way.
To put a watermark on the original image, you need to decode it, place the watermark, then encode it again. At the last stage, you will receive your quality loss. Moreover, if you use encoding parameters equivalent to the original ones, then the quality will drop even more: if the original picture was used for the first encoding, then for the second one it is already distorted.
Scared? This is the truth of life. But in practice, you need to play with the encoding parameters and select a satisfying ratio of quality and size of the output bitstream.