Virtually every cinema in the world is now digital.
While some cinemas have the option to play from BluRay, or other consumer formats, there is only one file format which is guaranteed to work: the Digital Cinema Package, or DCP.
If you want your film, trailer or advert to play with the least effort and with the best quality, you need to make a DCP.
It's just a collection of files, with a very specific format, in a folder. Some of the files contain video (picture) data, some audio (sound), some subtitles (if you have any), and some describe the DCP (its metadata, such as title, frame rate, and so on).
You give this folder to the cinema, and they can play it back, provided it is exactly right.
DCP-o-matic can take your files (MOV, MP4, WAV, AIFF and many other formats) and turn them into a DCP.
Sometimes it really is that easy: we are just talking about a conversion from one format of file to another. However, there are some things you should think about.
Encoding video to the DCP format with DCP-o-matic is slow; sometimes much slower than real-time. The files that are generated can be 100GiB (or more) in size.
In the beginning, DCPs could only be run at 24 frames per second (fps). This is changing, and many systems now support 25, 30 and in some cases higher rates like 48, 50 and 60. There is never any support for non-integer rates like 23.976.
DCP-o-matic can help you get around this problem, in some cases; it can (almost) seamlessly take 23.976fps content and make 24fps. However, if your content is not at 23.976fps or 24fps you will need to consider the cinemas that you want to play back in. Learn more about video frame rates...
If you are mixing and/or mastering your audio yourself, and especially if you are doing it using two speakers, there are some things to think about. Learn more about audio...
Since DCPs are so large, transferring them to the cinema for playback is not always easy. Many DCPs are transferred on USB external hard drives. However, the precise way that you format and write the files to the hard drive is very important, and can be difficult to get right (especially if you are using macOS). Learn more about DCP transfer...