How to start a newly created ffmpeg container correctly

Hey guys, I’m pretty new to Docker and hopefully I’m not posting this question at a wrong place.

I’m aware that we can run a container from the jrottenberg/ffmpeg image with the docker run command, as per documented on the image’s page on docker hub:

 docker run jrottenberg/ffmpeg \
            -i http://url/to/media.mp4 \
            -stats \
            $ffmpeg_options  - > out.mp4

But I’m having problem doing the same thing with the docker start command.

They way I understand, I should first pull the image and create a new container from it:

docker pull jrottenberg/ffmpeg
docker create --name my_ffmpeg jrottenberg/ffmpeg

But what’s the next step? I’ve tried the -a -i flags on the docker start command but still cannot get it to work. The error message is “you cannot start and attach multiple containers at once”.

This article seems suggesting that the command input is specified when creating the container? But I cannot figure out how that can be done.

Thanks for your time in advance!