How to find the key signature from video of a person playing.

[YammyFan]

Maybe, by looking at where the  KB player is putting his fingers it is possible to get a fair idea of the key he /she is playing in. But, I tried this and it is NOT all that accurate because sometimes accidentals are used when playing in the Key of C.. I know that some people have perfect pitch and that they would have no trouble recognizing the key signature of the song being played; but I wonder if mere mortals like me , are able to come up with the information.One way, to further interest in this topic ,would be to invite a member to post a video of themselves playing a song  showing their hands on their keyboard , and asking other members to guess what key signature. they are using.

[mikf]

You use your ears. You don't need perfect pitch. Play a few notes of the song on your keyboard. Then compare your playing to the  sound on the video. Doesn't even need to be a video, just a recording. Keep trying different keys till, they coincide. Shouldnt take more than two or three tries to get it right. If it is a video, you can also look at the lh chords on the video to help.
Mike

[ckobu]

Try using a chord tracker.
https://youtu.be/92aYTdA7tp8?si=OUIF-Mb7i8tFyOzo

[Robert van Weersch]

I don't have perfect pitch but just by trying, I'm always able to find the key signature within a few seconds.
Just try.

[mikf]

Agree Robert, you don't need perfect pitch just a feel for intervals, you play a couple of notes, move up or down a bit and get it by trial and error, as you say in a few seconds. You learn by just doing it, it's not hard.
Mike

[Toril S]

I can't always hear it right away just by listening, but by playing along with the song I find the key, no problem.