As someone who has been in the field for over seven years, I've accumulated an extensive skill set with a strong emphasis on the technologies you're seeking, which include Docker, Node.js, and AWS ECR. I have prior experience working with Amazon's ECR and have successfully built and managed Docker containers that incorporate Node.js and ffmpeg like you need with Editly package.
Moreover, I fully understand the importance of saving constant variables such as bucket name, region, aws access key to Lambda environment variables. Having worked extensively with AWS Web Services, I am well-versed in saving such variables and can ensure seamless integration. Similarly, my solid grasp of Python would provide easy maintenance of the Docker container code.
Finally, as a freelancer, my dedication is always to meet and exceed client expectations. I'll not only deliver but also include comprehensive instructions to alter Docker container code if you'd require changes in the future. With me on board, you can rest assured your project will be handled professionally, efficiently and on time. Thank you for considering my bid.