MP3 to M4A audio converter

Worked example

Convert MP3 to M4A (AAC) by choosing M4A as the export format and a bitrate no higher than the MP3's own; 192 kbps is the default.

MP3 to M4A decodes the MP3 and encodes the result again as AAC, so the new file carries the old MP3 artefacts plus a second round of compression. AAC at 128 kbps is efficient, but it cannot invent detail the MP3 encoder already threw away, which is why a 320 kbps output from a 128 kbps source only makes the file bigger.

Size math for a 4-minute track: a 128 kbps MP3 is about 3.84 MB (16,000 bytes per second × 240). Re-encoded at the default 192 kbps AAC it grows to about 5.76 MB, and at 256 kbps to about 7.68 MB, so every step above the source bitrate costs space without adding quality.

Typical case: a music teacher has a folder of 128 kbps MP3 practice tracks and the school app asks for M4A. Choose 128 kbps, leave Sample rate and Channels on Keep source, and avoid a resampling pass such as 44.1 to 48 kHz unless the destination demands it. The bitrate list offers 96, 128, 192, 256 and 320 kbps.

Common mistake: raising the bitrate to 320 kbps to "improve" the file. Fix: look up the MP3's bitrate in your player's file info first, match it, and keep the MP3 original. Check by playing the first and last ten seconds of both files, confirming the durations agree to about a second, and listening for swishy cymbals, a typical sign of stacked lossy coding.

sample.mp3

sample.m4a

Titles and cover art may not carry over, so check them in the app that will play the M4A.