Use AWS lambda to upload video into S3 with download URL
You could certainly write an AWS Lambda function that would:

Download the file from the URL and store it in /tmp
Upload to Amazon S3 using the AWS S3 SDK

It would be easiest to download the complete file rather than attempting to stream it in 'bits'. However, please note that there is a limit of 500MB of disk space available for storing data. If your download is larger than 500MB, you'll need to do some creative programming to download portions of it and then upload it as a multi-part upload.
As for how to download it, use whatever library you prefer for download a web file.
I want to upload video into S3 using AWS lambda function. This video is not available in my local computer. I have 'download URL'. I don't want to download it into my local computer and upload it into S3. I am looking for a solution to directly put this video file into S3 using lambda function. If I use buffer or streaming, I will consume lots of memory. Is there a better efficient solution for this?
I really appreciate your help.