I have a question. I am not a app developer, I want to send a s3 signed URL to my app developer so that he can upload video from app directly to s3 but the problem is that we also need to generate a thumbnail for the video being uploaded so that we can display it on app later on, is it possible to do it on the phone itself or app would upload it to a server where backend would generate the thumbnail and then we upload it to s3?