To be honest, it is more like 'apples vs oranges', but since it is about pipelines, I think I can bring some light to it. I do have a background with CircleCI, Jenkins, and GitHub Actions (yes, you can use that one too to do your transcoding and so on).

I had no prior experience with ConcourseCI until I read your post, but because I m very familiar with what you are trying to do (years as API Support Lead for vzaar.com) it was pretty simple for me to figure out the flow for ConcourseCI. Setting it in a docker is literally a few mins deal, just documentation is not exactly user-friendly.

So yes, you can use ConcourseCI, you can also add MinIO (https://min.io/) to set up S3 storage, - if you want to run it as a cluster, you need at least 4 computing instances or VPSs.