Cloudwatch Event ECS payload?

I see that I can run ECS tasks in response to Cloudwatch Events, such as a PutObject event in an S3 bucket. Like this:
https://docs.aws.amazon.com/AmazonCloudWatch/latest/events/CloudWatch-Events-tutorial-ECS.html

My use case is that I'd like to run an ECS task in response to S3 PutObject events, so that a container can do some work on an object whenever that objects gets uploaded to S3.

Does Cloudwatch Events send the event payload to ECS, the same way it sends event payloads to Lambda? If so, how is the event payload exposed to an ECS task? If possible I'd like my ECS task to be able to parse the event payload, inside the container of the ECS task, to determine the S3 object key which triggered the event which started the task.