SanDisk iXpand User Manual page 30

Videos
Supported file formats
MP4, MOV
For additional support, you may choose to download the SanDisk TopReel
application.
TopReel transforms your video experience by providing a beautiful way to
watch almost any common video format (MKV, WMV, HEVC, etc) on your
iPhone & iPad using the SanDisk iXpand Drive. It is optimized for iOS 11 and has
an elegant interface to complement super smooth playback.
TopReel supported file formats can be found here:
https://kb.sandisk.com/app/answers/detail/a_id/20671/~/sandisk-topreel-
supported-codecs