A free app for Windows, by 7thShare.

The Free 4K Blu-ray Player is a tool for playing Blu-ray and DVD files, including popular formats such as MKV, AVI, MP4, MOV, FLV, WMV, 3GP, AAC, AC3, etc. It is an all-inclusive media player software that can play any type of Blu-ray/DVD/3D disc, including common videos/audio, as well as 4K Ultra HD videos.
Fully support DTS5.1
It can play Blu-ray and DVD movies and videos with the best quality and sound. It also supports DTS5.1 and provides a super high quality of stereo output without loss. Moreover, you don’t have to worry about anything because this is designed for free.

Play Bru-ray movies/DVD/Folder/ISO image files and also 4K UHD/common videos.

Free 4K Blu-ray Player for Windows is officially authorized Blu-ray player software for Windows operating systems around the world. It can play all commercial and non-commercial Blu-ray discs, folders and ISO files in different regions on Windows computers. Besides playing Blu-ray movies, it also supports DVD and other video and audio formats, including 4K UHD videos, 1080p HD videos, MOV, AVI, MOV, FLV, WMV, MP4, MPEG, RMVB, MP3, WMA, AAC, AC3 and more.
With a simple and clear design, the versatile Free Blu-ray Player offers different screen modes like full, half, normal, double for you to choose. Besides, this Blu-ray Player enables you to choose your needed audio track and subtitle track as you like.