As you have a post count of 1 and so are presumably new I'll expand on the previous answer just a little.

Thge technique youwant is indeed chromakeying. Sometimes referred to as blue or green screening.

Simply film your actors in front of a blue screen, say. After you capture the footage you simple place it on the second layer of video in your editing application and apply a chromakey effect to the footage. This has the effect of making the blue in the shot disappear, showing the film layer below it. SO as long as video layer one is your sparkly background then you are done.

Easy.

However, if what you really want to know is how to create a suitable sparkly background then that's a different matter entirely.

Hope this helps.

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