Cant convert ISO file

I was given a movie (ISO file) by a friend. When I double click it, it mounts and I am able to watch the movie by simply opening the dvd player app. I want to be able to convert the file to an mp4 or m4v so I can watch it using apple tv, ipad, etc. I have tried simply using Handbrake, but when I try to find the source it says "no valid source." Also, if I navigate to the video_ts file itself, the file shows as empty, but clearly there is something there because I can watch the movie on the computer.

Does anyone know how I can covert the file or what program I might be able to use to do this?

I am using a newer macbook air and 10.8.5

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