When i received media messages my samsung strive sais unsupported format. How can i fix it?

My cousin tries to send me short video clips of my godson that he takes on his phone and everyone can get them but me. Sais unsupported format. Is it me or does the Samsung strive from att suck?|||Different cell phones use different formats. The easiest tool I found is to record on mailVU.com and send it to email addresses. It seems to always play, even on cell phones.