Can't play movies or video on android phone?

If youre having an HD android phone. There are times that you can't play movies. That's because not all video formats are supported by your android built in video player. They usually support only mp4, AVI, MPEG, But not all mp4, avi or mpeg are supported because it depends on what the codecs is used during encoding.

To address this issue, just install a VLC media player for your android device. You can get it at Google Play Store for free.VLC is a free and open source cross-platform multimedia player and framework that plays most multimedia files as well as DVDs, Audio CDs, VCDs, and various streaming protocols.It plays most codecs with no codec packs needed:
MPEG-2, DivX, H.264, MKV, WebM, WMV, MP3 etc...

exFat for Android

Are you wondering why you can't copy more than 4gb of a single file on a micro sdcard?Its because your're sdcard is formatted to a Fat32 file system which  is the default file system for micro sdcard. A Fat32 limit only up to 4gb of a single file to be stored in an sdcard.  So if you're copying an HD movies that are morethan 4gb of file, it will not be copied. Unless you format you're sdcard through a computer to an exFat file system..  An exFat file system is a Microsoft file system optimized for flashdrives that can be used where the NTFS file system is not a feasible solution due to the file size limit of a standard fat32 file system.

So if you are planning to copy a large file of data in the future that is morethan 4gb, specially HD movies, I suggest to format you're micro sdcard to an exFat file system to avoid incompatibility or error that may occur in the future.