I saw a video
Today I saw a video about the effects of several ways on losing weight. It analyzed the effects from two aspects of eating different foods and exercising on it.
I "watched" a video. Watching means you make an effort to see it. If you "see" something, usually it means it was not on purpose.
1) Today, I watched a video that talked about several ways to lose weight.
Today, I watched a video that discussed different ways of losing weight.
You wouldn't use the word "effects" because this is related to the result.
We are talking about how to lose weight, not what happens after you lose weight.
2) It analyzed this process two different ways: Eating food and exercising.
The video analyzed the results of two different ways to lose weight: through diet and through exercise
Hope this helps!