The problem has been resolved. The solution is to extend the pre-built container
by following the procedure at Extend a Pre-built Container - Amazon SageMaker
The “extension” is just to add RUN pip install decord.
Also ensure the IAM role attached to your Sagemaker notebook has this permission,
AmazonEC2ContainerRegistryFullAccess
If not, proceed to add it.
Once I did these, I was able to predict successfully.