OSDb is a protocol first introduced on the ​OpenSubtitles web site. Its main purpose is to eliminate the painful process of searching for subtitles on the web and make finding subtitles to your videos as fast and simple as possible.
EXACT MATCHES - instead of having a lot of subtitles matched to a single movie title (or lately IMDb ID), they are assigned directly to a specific video file (using a specific fast hash function). So when searching for subtitles to a specific video file you'll only get those that (according to other users) match your video file 100%.
SPEED - instead of searching for subtitles on the web site, you can use applications built to support this protocol that offer a user-friendly UI to allow easy and fast search and download of subtitles.
Please keep in mind that this is a new concept (as opposed to other subtitle web sites that are here for quite some time) so the number of available subtitles is lower than can be found on the web. Nevertheless the more people use this system, the more subtitles will be available over time.
So don't give up on us, we believe this is a concept worth looking into and contributing.
OSDb is based on ​Gabest's ISDb design which is an online distributed subtitle database that first introduced this concept along with a 'distributed database' approach.
You can of course select what subtitle languages you are interested in to avoid having too many matches in languages you don't even speak.