How to batch convert AAC files to MP3

If you have a handful of AAC files from Voice Memos or a podcast app, converting them one by one is fine. But when you are dealing with an iTunes library, a folder of audiobook chapters, or a batch export from a DAW, doing files individually is tedious. Batch mode lets you drop the whole set, walk away, and come back to a folder of finished MP3s.

Most online converters cap free batches at 2–5 files, throttle speed, or force you to upload every file to their server. Because the AAC to MP3 converter runs client-side in a Web Worker, there is no upload step, no server queue, and no artificial throttle. The limiting factor is your device's CPU — and on any machine from the last five years, a 4-minute song encodes in about 2–3 seconds.

Songs purchased from the iTunes Store are DRM-free 256 kbps AAC files with an .m4a extension. If you want MP3 copies — for a car stereo, an older MP3 player, or a DJ controller that only reads MP3 — batch conversion is the fastest path.

1. On macOS, find your music in Music > Settings > Files > Media Folder Location (usually ~/Music/Music/Media). On Windows, check iTunes > Edit > Preferences > Advanced > iTunes Media folder.
2. Open the converter in your browser and drag up to 20 .m4a files onto the drop zone.
3. Set the bitrate to 256 kbps to match the source quality. Going higher than 256 adds file size without adding detail, because the source is already lossy at 256. The quality guide explains why.
4. Click Download all MP3s when the batch finishes, then drag the next 20 files in.

Apple Music streaming tracks are DRM-protected and cannot be converted by any tool. If a file fails to decode, it is most likely a streaming cache rather than a purchased track.

When you batch-convert 20 files on a server-based converter, you are uploading up to 2 GB of audio to someone else's infrastructure. That might include unreleased music, client recordings, legal depositions, or private voice notes.

The browser-based converter never sees a network request for your audio. The browser's built-in AAC decoder reads the file from disk, a JavaScript LAME encoder produces the MP3, and the result is saved back to your downloads folder. You can verify this by opening DevTools (F12) and watching the Network tab — zero audio bytes leave your machine.

In batch mode every file gets the same bitrate, so pick the setting that fits the majority of your files:

If a batch contains mixed content and you are unsure, 192 kbps is a safe middle ground — transparent for speech, good enough for casual music listening, and about 1.5 MB per minute.

The browser converter handles batches of up to 20 files, which covers most one-off conversions. For a full music library with hundreds or thousands of tracks, a command-line tool is faster. ffmpeg is free, open-source, and available on macOS, Windows, and Linux:

# Convert every .m4a in the current folder to 256 kbps MP3
for f in *.m4a; do
  ffmpeg -i "$f" -codec:a libmp3lame -b:a 256k "${f%.m4a}.mp3"
done

On Windows (PowerShell):

Get-ChildItem *.m4a | ForEach-Object {
  ffmpeg -i $_.FullName -codec:a libmp3lame -b:a 256k ($_.BaseName + ".mp3")
}

For smaller batches or when you do not want to install anything, the browser converter is simpler — drag, convert, download, repeat.

The converter works on mobile browsers too. On iPhone and iPad, tap Choose AAC files and multi-select from the Files app. On Android, Chrome lets you select multiple files in the system file picker.

Mobile conversion is slower than desktop — an iPhone 15 takes roughly 4–5 seconds per song versus 2–3 seconds on a laptop — but it works without any app install and the audio never leaves your phone. For batches under 10 files it is perfectly practical.