Sleep Mode when Watching Video on Browser

[oscarb]

elementary OS 0.4.1 Loki
Built on "Ubuntu 16.04.3 LTS"
Linux 4.4.0-101-generic
GTK+ 3.18.9

When watching video on my browser (e.g on youtube, browser with Firefox 57.0.1 (64-bit) ), I see the warning on the right top corner, stating the computer will go in sleep because it was inactive for a while(15 mins currently in my case). Since I am watching the video, I do not use my mouse or keyboard.

Also, to deactivate "sleep when inactive for" setting is not an option I would choose, because I find it useful.

It would be great, if the os knows that I am watching video and does not take it as the user is inactive.

I searched bugs, but I could not find this one. Hope it is not a duplicate.