MP4 to M4A Converter

How it works

1. Choose an MP4 above. The file card shows the sound codec.
2. If it says AAC, the page confirms the sound will be copied as it is. Press the button.
3. Download the M4A. A long file finishes in seconds because nothing is decoded.

Copying versus converting

Most converters decode audio and encode it again even when they don't need to, which costs time and a little quality. When the source and destination use the same codec, the better move is a stream copy: the compressed audio frames are moved into a new container untouched. That is what happens here for AAC sound, which covers nearly all MP4s from phones, cameras, editors and screen recorders.

If an MP4 holds a different sound codec, such as MP3 or AC-3, the tool encodes it to AAC instead and tells you so on the result card.

Why M4A

• It is the native audio format for Apple Music, iTunes, GarageBand and Voice Memos.
• It is smaller than MP3 at the same quality, because AAC is the more efficient codec.
• It supports chapters and cover art, which is why audiobooks often use it.
• The file is exactly as good as the video's soundtrack, with nothing added or removed.

If a device or app you use can't play M4A, use MP4 to MP3 instead; MP3 is the one format everything plays.

Speed and size

Our test copy of a 20-second clip took a tenth of a second, and long files scale the same way: the work is reading and writing bytes, not processing sound. The M4A is roughly the size of the MP4's audio portion, typically a small fraction of the whole video.

Using the M4A with mydubly

M4A is one of the formats mydubly transcribes directly; see M4A to text. Uploading an M4A instead of the full video means far less to send.

How the free converter works

The converter is ffmpeg, the open-source media toolkit, compiled to WebAssembly so it runs inside your browser tab. Your file is read straight from your disk by that engine; it is never uploaded to mydubly or anywhere else, and no account is needed.

• The engine is about 30 MB and downloads the first time you convert something. After that your browser normally keeps it.
• Large inputs are fine because the file is read in place, but the result is built in memory, so outputs are capped at about 1.5 GB.
• Speed depends on your device. Copying streams takes seconds; re-encoding video is the slow case.
• Keep the tab open until the download button appears. Closing it stops the conversion.