MediaConvert Error : AssumeRole failed

I understand your frustration with the MediaConvert error you're experiencing. The error message suggests that there's an issue with the IAM role permissions needed to access the S3 bucket containing your input file. This is likely due to incorrect or insufficient permissions set up for the IAM role used by MediaConvert.

To resolve this issue, you should check and update the following:

1. Ensure that the IAM role assigned to MediaConvert has the necessary permissions to access the S3 bucket where your input file is stored. The role should have, at minimum, read access to the input S3 bucket.

2. Verify that the IAM role has the correct trust relationship established. MediaConvert needs to be able to assume this role to perform its operations.

3. Double-check that the S3 bucket policy allows access from the IAM role used by MediaConvert.

4. Make sure that the IAM role has the required permissions to perform the iam:PassRole action. This allows MediaConvert to pass the role to other AWS services as needed.

5. If you're using server-side encryption on your S3 objects, ensure that the IAM role has permissions to use the encryption key (KMS permissions if applicable).

To troubleshoot, you can:

1. Review the IAM role's permissions in the IAM console.
2. Check the S3 bucket policy to ensure it's not restricting access.
3. Verify that the MediaConvert job settings are correctly specifying the IAM role.

If you continue to face issues after checking these points, you may want to temporarily grant broader permissions (such as S3 full access) to the IAM role for testing purposes. Remember to restrict the permissions again once you've identified the specific permissions needed.

Lastly, keep in mind that when replicating your setup in a new account, you need to recreate all the necessary permissions and trust relationships. The IAM roles and policies from your previous account won't automatically carry over to the new one.

If you're still unable to resolve the issue, consider reaching out to AWS Support for further assistance.
Sources
Error codes - MediaConvert
Troubleshooting AWS Elemental MediaConvert identity and access - MediaConvert