A free app for Android, by The AppGuru.

This handy tool lets you convert VOB files to MP4 in a few taps. Vob To Mp4 Video Converter features a built-in file scanner and search function for easy file finding. All VOB files — which are arranged in alphabetical order — can be viewed on the app. 

Pertinent file information such as location and file size are also included. When you convert a VOB file, the app shows a progress bar as well as the remaining conversion time. There’s even an option to choose your preferred video resolution. You can play, share, or delete the video once you’ve converted a VOB file. Vob To Mp4 Video Converter is free on the Play Store.