I'm going to reply to this old thread because I came across it on Google, trying to search how to attach vids to MMS on Android. I figure I'll post my solution so others can benefit. I ended up finding an app called VidTrim which will shrink your videos and make them small enough to send through MMS. I had a 5 second, 1080P video which came in at 6MB. VidTrim shrunk it to 240p size, and it came out to 133KB, with sound! The app was easy to use, and converted the video in 10 seconds. Easily sent through Google Hangouts MMS.