So...looks like we can by default have these formats:
.MP4, .M4V (MPEG-4)
.MOV (QuickTime)
.WMV (Windows Media Video)
.AVI
.MPG
.OGV (Ogg)
.3GP (3GPP)
.3G2 (3GPP2)
More info here:
https://premium.wpmudev.org/blog/video-wordpress/
I also looked up the phone formats for Android, Samsung, iPhone and found generally they're mp4, .mov files so we should be okay for compatible formats.
Video file formats that should be included in extensions, keeping in mind that users will be recording videos from their mobile phones / tablets.