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  dBpoweramp Codec Central: m4a, mp4, m4b & aac

 m4a. mp4, m4b & aac  




mp4 Codec



Successor to mp3, m4a (and mp4) made popular by iTunes and iPods. mp4 is a container that can store many sub-formats:

  • Advanced Audio Compression (AAC), of which are different types: LC (low complexity), HE (high efficiency) to name a few. To encode your audio to be compatible with most audio players, use the LC compression type (used as default by this encoder). High Efficiency (HE AAC) uses SBR technology (not too different as mp3PRO) if the player knows about HE the extra frequency information can be decoded, otherwise half the audio quality will be missing on playback. A newer standard again for ultra low bitrates is AAC+ or AAC HE v2, this uses parametric stereo for even lower bitrates, dBpoweramp is able to decode every AAC type (excluding iTunes m4p protected). 
  • Apples Lossless format (ALAC) this format is like Zip for audio and looses no audio quality (audio tracks purchased from Apples iMS store are lossy aac).

File Extensions:

  • .m4a are audio content only,
  • .mp4 can contain both audio and video,
  • .m4b these are identical to .m4a except the iPod knows to use them as audio books and allow book marking,
  • .m4v are video files.
  • .m4p protected audio format (tracks purchased from iTunes Music Store are protected), whilst dBpoweramp cannot decode these see Forum for details on fair use.

Adding ID tags to mp4 has standardized on the Apple iTunes format, although a competing Nero tagging format has emerged.

Decodes   .m4a, .mp4, .m4p, .aac      Encodes   .m4a (Apple Lossless, AAC: LC, HE & HE v2)