Changing video content type (mime type) in CDN
Found the Answer : 

1)  "A MIME-TYPE is a server side setting. You can ask your hosting provider to add the MP4 MIME-TYPE for you.

Or, you can add a .htaccess file to the directory where you uploads are stored".

A sample .htaccess file that adds the MP4 MIME-TYPE is:

&lt;IfModule mod_rewrite.c&gt;
  AddType video/mp4 .mp4
&lt;/IfModule&gt;"


Source : Need to Change Video Content Type to video/mp4 so it plays in IE

But this did not work for me for some reason 

2) I did the change in my core class file which i was using in drupal module for CDN upload 
I had made a change in my class.s3.php file -> in mime_type[] array and also, cross checked with putObject() function.

**


  Setting of mime type is always done in coding side and not in AWS S3
  bucket, We need to use AWS PHP Class file or sdk to do the
  manipulation in mime type or make the necessary changes in core class
  file (eg. class.s3.php )


**
 For details check here find-mime-type-of-file-or-url-using-php-for-all-file-format

Second Answer has worked for me :)