بسم الله الرحمن الرحيم
If you ejected semen merely by watching the video and you did not masturbate to eject it then your fast did not break in the above mentioned case. So you are not required to make its qaza. (Shami: 3/367)
But it is noteworthy that in no way it is lawful to watch videos with pictures of women. You committed a big sin by watching video in the state of fast. You should do taubah from it wholeheartedly and avoid watching videos in future altogether. In case you want to know anything about religion then you should ask it any reliable scholar directly or by phone etc. Internet contains each types of information and until it is not confirmed by any reliable and authentic scholar one should not believe it.
Allah knows Best!
Darul Uloom Deoband
This answer was collected from the official ifta website of Darul Uloom Deoband in India.