Its a popular video format, we should recognize its type.
This will also prevent people from uploading mp4's to commons.
Wikipedia claims m4a sometimes used for video content.
RFC 4337 says audio/mp4 is mime type for mp4 with no
video (which is usually what an m4a extension means).
Bug: 52990
Change-Id: I5c24c3e318651241cced5b36d107d3603a289427
audio/mpeg audio/mp3 audio/mpeg3 [AUDIO]
+audio/mp4 [AUDIO]
audio/wav audio/x-wav audio/wave [AUDIO]
audio/midi audio/mid [AUDIO]
audio/basic [AUDIO]
video/x-flv [VIDEO]
video/webm [VIDEO]
video/x-matroska [VIDEO]
+video/mp4 [VIDEO]
application/ogg application/x-ogg audio/ogg audio/x-ogg video/ogg video/x-ogg [MULTIMEDIA]
text/x-setext etx
text/x-sawfish jl
video/mpeg mpeg mpg mpe
+video/mp4 mp4 m4a m4p m4b m4r m4v
+audio/mp4 m4a
video/ogg ogv ogm ogg
video/quicktime qt mov
video/vnd.mpegurl mxu