MP4 to M4A Converter

Most MP4 videos already carry their sound as AAC, the same audio format that M4A files use. So turning an MP4 into an M4A does not need any re-encoding: the AAC stream is copied into an audio-only MPEG-4 file, bit for bit, in a few seconds — the quality is exactly the original's. Use it for lectures, podcasts, concert videos or voice memos you want in a music app or on an iPhone. Videos with other sound formats are encoded to AAC. It runs in your browser; nothing is uploaded.

How to use this tool

1. Choose one or more MP4 (or MOV, M4V) videos.
2. Keep "Keep the original AAC sound", or pick a bitrate to re-encode to a smaller file.
3. Optionally enter a start and end time, or another audio track.
4. Download the M4A files.

Formula

Copy: M4A size ≈ original audio bitrate × length ÷ 8 · Re-encode: size ≈ chosen bitrate × length ÷ 8

An M4A is an MPEG-4 file with only an audio track; iTunes, iPhones, Android and most players read it. Copying keeps the sample rate, channels and quality unchanged, and cutting while copying starts on the nearest AAC frame (within about 1/40 of a second). Re-encoding uses the AAC encoder of the ffmpeg engine; surround sound is kept and encoded at 384 kbps.

Example

A 50-minute lecture video with 128 kbps AAC sound becomes an M4A of 128,000 × 3,000 ÷ 8 = 48,000,000 bytes, about 46 MB, copied in seconds. Re-encoded at 64 kbps it would be about 23 MB.