Removing black is easy: it is basically the luma equivalent of a chroma key.

A much more interesting technique, that might be useful for you some day, is the ability to remove any background that doesn't move. If your camera is locked down, and if the background doesn't move (e.g., a stage backdrop), and if you have at least one frame that contains just the static background (or if you can create the static background by merging several frames with the actors covering different parts of the background), then you can use a "difference matte" to, in essence, do a green screen.

Here is a link to something I've shown before. A decade ago, when "American Idol" was brand new and "trending," a friend of mine was planning a surprise party in Las Vegas for his wife, and wanted to have the centerpiece of the party be him singing "Happy Birthday" to her, but do it as a contestant on American Idol. He recorded his schtick at his house, by stepping in front of the camera and performing. He did not use a green screen. He sent the tape to me along with his "American Idol" DVD which contained highlights from the first two seasons. I found appropriate clips on that DVD, including one that had a long shot of the set, and mixed them together, using the "difference matte" to composite him into the AI set. This was the result:

American Idol Happy Birthday

Right click, Save As, and play.