Convert AAC to MP3

How to Convert to MP3

1. 1

   Add your AAC files

   .aac, .adts, .adif and AAC inside .m4a, up to 200 MB each, twenty at a time.

2. 2

   Choose a bitrate

   192 kbps matches most AAC sources. Turn on repair if the file came from a stream capture or a failed download.

3. 3

   Click Convert and download

   The result is a standard MP3 that plays anywhere.

Raw AAC and AAC in a container are different things

A file ending in .aac is usually a bare ADTS stream: a sequence of frames, each with its own small header, and no container around them. AAC inside an .m4a is the same audio wrapped in an MP4 box that adds a duration, an index and space for tags. Both convert here. The distinction matters because a bare stream has no index, so nothing in the file says how long it is or where to seek, which is why players often show the wrong duration for a .aac and why a truncated one still opens and plays until it runs out.

The repair mode, and what it can and cannot do

Bare AAC turns up most often as a capture from a stream, and captures get truncated, dropped and corrupted in ways that a properly muxed file does not. When a frame header is damaged, a strict decoder stops at that point and reports failure, leaving you with nothing, even though the ninety per cent of the file before the damage was perfectly fine. Turning on repair tells the decoder to skip frames it cannot parse and regenerate the timestamps instead of giving up. What comes out is the readable audio with a gap where the damage was. What it cannot do is invent the missing part, and a file damaged in its first frames may still yield nothing. It is off by default because on a healthy file it does nothing and only slows the decode.

Two lossy formats in a row

AAC is generally better than MP3 at the same bitrate, which is why streaming services and Apple chose it. Converting to MP3 means decoding what AAC kept and then discarding a slightly different set of information, because the two encoders disagree about what is inaudible, so a second, smaller loss is unavoidable. Setting the bitrate at or a little above the source keeps that loss below what you will notice. There is no benefit to 320 kbps from a 128 kbps AAC: the detail is already gone and the larger file stores the same sound.

Why anyone still converts to MP3

Compatibility, and nothing else. AAC is the better format on paper, but a fifteen-year-old car stereo, a cheap hardware player, an old DAW or a piece of broadcast software may read MP3 and refuse everything else. If the destination handles AAC, the best conversion is not converting.

Frequently asked questions