I added this 25 mb size video to show what I couldn't explain with words ,I know this just community forum page can you send this to a support team thanks Albert
You can find many tutorials using Green Screeen effects on Youtube - the principal is the same whichever software is being used.
. . . how do I take lets say a green screen blood effect and add it into a river video to only effect the body of the river to stay within the trame of the water . . . .
Do you have an example of what you are trying to achieve - is it a river flowing with blood or do you want the water flowing like blood?