How to convert video to 2.35:1 aspect for movie theater looking video

Ingo created a youtube video on how he converted a 16:9 Cinelerra video to 2.35:1.  For those non-artists who like me had no idea what 2.35:1 is, here is a quote from the internet -- "Cinemascope or Anamorphic Format: 1.0 to 2.35 or 2.35:1 - The Widescreen Cinemascope format (commonly called the 2.35:1 aspect ratio) has become the established medium for movie theater or “Big Screen Cinema” presentations that may vary from 2.35 to 2.40 and even wider formats.  The youtube video has a couple of minutes showing the media format, but a few seconds before 4 minutes in shows how he calculated getting to 2.35.

https://www.youtube.com/watch?v=ZG7yCj3uLjE