Using Untrunc to repair video files - can't quite understand the format for running the command

I am using https://github.com/synctree/docker-untrunc to try to repair videos. I get to the stage of running the command:

docker run -v /some/directory:/volume/in/container -it synctree/untrunc /volume/in/container/good-file.mp4 /volume/in/container/bad-file.mp4

but it seems I don't understand the format of this command clearly enough as I am getting back 'Could not open file: /Downloads/recup_dir.1/GH011183.MP4' errors when running the following command:

docker run -v /Users/marcwatts/Downloads/recup_dir.1  -it synctree/untrunc /Downloads/recup_dir.1/GH011183.MP4  /Downloads/recup_dir.1/f270416128.mp4 

Can someone who understands Docker/COmmand Line commands better than me help with what parts of this command I am inputting wrong?

The files are both in the same folder inside Downloads, 'recup_dir.1'.