The file extension AC3 identifies audio files in the so-called Adaptive Transform Coder 3 format. It is a lossy coding process from Dolby Laboratories for digital multichannel audio streams.
The AC3 sound format is mainly used for digital sound transmission in the TV area as well as DVDs and BluRays. It supports up to 6 channels (Dolby Digital EX up to 8), with 3 front, 2 rear channels and one for the subwoofer. Therefore, the usual 5.1 is often indicated with 3 / 2.1.
On DVDs and BluRays AC3 files are hard to find, as the audio streams are contained in the respective container (vob or M2ts). Ac3 files are mainly used in the production of video files, DVDs and BluRays for integration into other containers.
Only for music files AC3 is often used directly, as many media boxes as well as DVD and BluRay players can play AC3 files directly.
It should be noted that some programs can not load AC3 files directly, but need a plugin, such as Quicktime or Windows Media Player (ac3filter).
Most often resolving problems with opening AC3 files is very simple. Just install an appropriate program that supports such files. All of the listed programs support AC3 files, but may vary in offered function and purpose. Some programs may be capable only of viewing contents of AC3 files or offer file conversion options, but may not be capable of editing such files.
It is possible that although a compatible program has been installed on user’s system, it is not used by the system to open it. This may happen because no default application was associated with this type of files. To associate AC3 files with given application, select "Open with" from drop-down menu (accessed by right-clicking on the file). Then select from the list the program or application you want to be used to open this type of file. If the QuickTime Player applications is not on the list, select "Browse" option in order to manually locate the directory where QuickTime Player has been installed.
Sometimes problems with opening AC3 files may not lie with the application itself, but can arise due to other causes, such as: