iOS Recorded Video Playback on Android

I am trying to record video from iPhone device using UIImagePickerController and able to store it in MP4 format. The same video is uploaded on the Amazon S3 cloud.

When I try to play the same video on Android devices, it fails to play with an error, cannot play.

I searched forums/google and found that ffmpeg should be used to compress the video before uploading. I want to do the compression on the phone itself rather than on the server. Which is the best way to achieve this?

Regards,

Nirav