Definition of MP4 noun from the Oxford Advanced Learner's Dictionary

 

MP4

 noun
noun
BrE BrE//ˌem piː ˈfɔː(r)//
 
; NAmE NAmE//ˌem piː ˈfɔːr//
 
[uncountable, countable]
 
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a method of reducing the size of a computer file containing sound and images; a file that is reduced in size in this way You can convert video to MP4.
See the Oxford Advanced American Dictionary entry: MP4