I was so pleased to find Video DownladHelper — after trying a half-dozen others that were unreliable, didn't work on sites/content I needed to save, or worse.

If the browser can play video and audio content, it seems simple enough to save it locally. The reality of streaming web content is anything but simple, neither is building an extension to capture and store it. The developers and volunteers who maintain Video DownloadHelper put in an incredible and ongoing effort to keep it working on nearly every site where there is video and audio content.

And for most uses, you will pay nothing.