A VOB file (Video Object) is a container format in DVD-Video media. VOB can contain video, audio, subtitle, menu and navigation contents multiplexed together into a stream form. VOB is based on the MPEG program stream format, but with additional limitations and specifications in the private streams.The MPEG program stream has provisions for non-standard data (as used in VOB files) in the form of so-called private streams. VOB files are a very strict subset of the MPEG program stream standard. While all VOB files are MPEG program streams, not all MPEG program streams comply with the definition for a VOB file.
VOB is a popular file format for commercial DVDs. However, many commercial DVDs contain security information and encryption to protect the contents of a DVD. If you try to rip a VOB file from a protected DVD, you're likely to encounter errors and be unable to manipulate the file. Keep in mind that video piracy is illegal, and you're better off not trying to rip protected VOB files.
Apple's DVD Player application can play VOB files in DVD VIDEO_TS folder. And VLC media player and MPlayer can also play VOB files. But when you attempt to import VOB files into iMovie for editing, you'll find it unrecognized by iMovie. In such case, you'll need to convert VOB to iMovie MOV or other well-supported format for iMovie.
iOrgsoft Video Converter for Mac allows Mac users to convert VOB files to other popular video file formats like MOV, MP4, H.264, etc for playback on different video player, for further editing on common editing software like iMovie, FCP, FCE, etc, for transfer to portable devices like iPad Air, iPad Mini, iPhone 5S, iPhone 5C, iPhone 4S, iPod Touch, Kindle Fire, Google Nexus, Samsung, etc.