uploaded media file got very slow buffered streaming

Hi AWS-User-6219742,

A extremely common reason that could cause slowdown when streaming a video from a S3 bucket is the size of the video in the bucket. Most original videos tend to be larger in size than necessary, so optimizing the video may help. Also using Amazon Cloudfront in conjunction with a S3 bucket is known to improve video streaming. 
 
Here are some resources that could help:
https://aws.amazon.com/blogs/networking-and-content-delivery/amazon-s3-amazon-cloudfront-a-match-made-in-the-cloud/
https://css-tricks.com/streaming-optimized-videos-from-aws-s3-in-minutes/