option to use local nativ ffmpeg instead of ffmpeg-static

[Fabioni]

Hey, I had some problems with ffmpeg, so a solution for me was to just change in index.js

// @ts-check
const ffmpegPath = /** @type {string} */ (
  /** @type {unknown} */ (require('ffmpeg-static'))
);

to

const ffmpegPath = "ffmpeg";

Since ffmpeg is installed on lots of systems anyway, I think there should be an option to say that we just want to use the ffmpeg that is already available in the path.