Credentials can be set explicitly on an S3 storage. However, when running within an EC2 or ECS environment we recommend assigning an IAM role to the server. This way, server credentials can be used when accessing S3 storages and other AWS services.
We recommend that you separate source and destination storages. A source storage is where you would keep the original files while a destination storage should hold everything that is generated by Accurate Video.
Make sure that the bucket you setup as a source storage is read-only.
The buckets can be connected to Accurate Video as storages using either the UI or through the REST API. Having the bucket policies in place, there is no need to apply any explicit credentials. In the UI, just select "Use server credentials".
Configure storage access and tags according to this example.