AAC to MP3 Converter

How to convert AAC to MP3

The converter reads each file's header first, so you see its length and the MP3 size before you convert.

1. 1

   Add your AAC files

   Drag .aac files onto the converter or click to browse. AAC inside .m4a, .m4b or .mp4 works too. Up to 10 files go in the list, each up to 100 MB and 30 minutes.

2. 2

   Pick the bitrate

   128 kbps is the default and suits speech and most music. Go higher if the AAC was high quality and you want to keep as much of it as you can; pick Mono for a voice recording if you like.

3. 3

   Convert and download each MP3

   Convert runs through the list one file at a time. Each MP3 gets its own preview and Download button and keeps the original name with a .mp3 ending. Change the bitrate and convert a file again at any time.

When an AAC file needs to be an MP3

AAC is a good format: MDN calls it the standard audio format for Blu-ray discs and HDTV and the format of songs bought on iTunes. The trouble is the device or site on the other end.

• Car stereos and older players

  Some car head units, USB sticks and older MP3 players read MP3 but not AAC. A folder of MP3s plays where a folder of .aac files may show up empty or skip.

• Podcast hosts and upload forms

  Some hosting platforms, course sites and client portals list MP3 as the upload format. Converting gives them the file type they ask for without re-recording.

• Editors and older software

  Some audio editors, DJ tools and older Windows programs open MP3 but not a .aac file. MP3 is the format they are most likely to take.

• One format for a mixed folder

  Recordings from a phone, a recorder and a video's audio track end up as .aac, .m4a and .mp4. Converting them all to MP3 at one bitrate gives you one kind of file to share and play.

Two kinds of AAC file

The extension does not always say what is inside, so the converter reads the first bytes of each file and shows the kind next to its name.

1. 1

   AAC (ADTS): the .aac file

   A bare stream of AAC frames, each with a small header. MDN describes ADTS as an almost bare stream of AAC audio meant for streaming, such as internet radio. There is no index, so the converter estimates the length from the first frames.

2. 2

   AAC in M4A or MP4

   The same audio inside an MP4 container, with the length and format stored in the header. An .m4a can also hold Apple Lossless instead of AAC; MDN lists Safari as the only browser that decodes it.

3. 3

   Not sure? Add it anyway

   A file that is neither is refused by the browser's decoder with a clear message, and nothing else in the list stops. Voice Memos from an iPhone have their own page, the Voice Memo to MP3 Converter.

How big the MP3 will be

An MP3 at a set bitrate grows by the same amount every second: bitrate × seconds ÷ 8 bytes. The converter shows the size for each of your files before you convert. MDN notes that AAC was designed to give more compression with higher fidelity than MP3, so an MP3 may need a higher bitrate than the AAC had to sound as good; pick one step higher when quality matters.

Which browsers convert AAC