AC3 or Dolby AC-3 is a data format file where six audio channels are compressed by the AC3 codec, also known as Audio Codec 3. The AC3 format is used for the following audio formats - DVD, Blu-ray, cinemas and game consoles. To play the full surround sound of the AC3 file signal, you need a device that supports Dolby Digital technology.
Mp3 is the most popular and widespread audio format. It was created by MPEG team in the 90s of the last century. MP3 format provides the quality of sound reproduction, similar to the original sound. The MP3 format is based on a lossless compression algorithm made to reduce the data size. In other words, music streams are compressed and deleted in the format that are somehow similar for listening on devices of common use.