Convert MP4 to M4A
Pull the audio out of an MP4 as an M4A without re-encoding it. An MP4 almost always holds AAC already, and an M4A is an MP4 container holding an AAC track — so the audio can simply be lifted from one to the other. What you get is bit-for-bit identical to what was recorded, and it takes about as long as copying the file.
Use this without the search next time. Prathom Workbench puts Prathom's tools in your toolbar.
Add to Chrome — freeDrop your MP4 file here, or click to browse
Up to 50 MB. Deleted automatically after 30 minutes.
What it does
- The AAC track is copied, not re-encoded
- Bit-for-bit identical to the source audio
- Finishes in about a second
- No watermark and no sign-up
How to use MP4 to M4A
- 1
Add the MP4
Drop the file in or choose it from your computer, up to 50 MB, no account needed.
- 2
Convert
The video is discarded and the AAC audio track is copied into an M4A container. Nothing is decoded and nothing is encoded.
- 3
Use it
The M4A plays on every Apple device, in podcast software, and anywhere else that reads AAC.
The extraction that costs nothing
Most audio extraction is a re-encode: the sound is decoded out of the video and compressed again, which takes time and loses a little. This one is not.
An M4A is an MP4 container holding an AAC track. An MP4 is an MP4 container holding an AAC track and a video track. So extracting the audio means taking one track out and leaving the other behind — a copy, not a conversion. The bytes that come out are the bytes that were recorded.
How it works
The video stream is discarded and the audio stream is copied into a new
container with -c:a copy. Nothing decodes. Nothing encodes. The operation is
bounded by how fast the file can be read.
The source is probed first, because the copy is only valid if what is inside really is AAC. If it is something else, the audio is re-encoded to AAC instead and you get a valid M4A one generation removed. That fallback is automatic and rare.
Why this site kept recommending it before it existed
Several pages here already told readers to do this. mov-to-mp3 says that copying
the AAC track out into an .m4a is instant and lossless and is the better route
where the destination accepts it. mp4-to-wav says the same.
Both were true of ffmpeg and, until this page, false of this converter — the M4A target re-encoded. Advice that the tool behind it does not follow is worse than no advice, so the converter was changed rather than the sentences.
When MP3 is still the right answer
Reach for MP3 when you do not control what plays the file: a car stereo of unknown age, a colleague's laptop, a transcription service with a fixed list of formats. MP3 is worse and is refused by nothing.
Reach for M4A when you do know — an iPhone, a Mac, podcast software, a recent car. You get the original audio rather than a copy of it, at a smaller size for the same quality, and the conversion is instant.
What "lossless" is worth, and when it is not
For speech it is worth very little in audible terms. A voice re-encoded once more at a sensible bitrate is not something anyone identifies in a blind comparison, and if the destination needs MP3 there is nothing to agonise over.
Where it matters is anything that will be edited, mastered, or converted again later. Every generation of lossy encoding is permanent and they accumulate: an MP3 made from an M4A that was re-encoded from an MP4 has been through three encoders, each discarding what it judged inaudible on top of what the last one left.
Extracting without re-encoding stops that chain at one. It costs nothing and takes less time than the alternative, which is the unusual case where the better option is also the cheaper one.
Examples
A recorded talk for a podcast editor
Podcast software works natively in AAC. Handing it an untouched track means the edit starts from the recording rather than from a copy of it.
An interview for archiving
A fraction of the video's size, with the audio unchanged. The right thing to keep when the pictures were never the point.
Frequently asked questions
Is this really lossless?
Yes, when the MP4 holds AAC — which nearly all of them do. The track is copied from one container into another without being decoded, so the bytes are identical. This was verified rather than assumed: extracting from a pink-noise test file produced an audio stream whose MD5 matches the source's exactly.
What if the MP4 does not hold AAC?
Then the audio is re-encoded to AAC instead, because a container cannot hold a codec it has no way to describe. That is rare for an MP4 and it happens automatically — there is nothing to choose. The result is still a valid M4A, just one generation removed rather than zero.
Should I use this or MP3?
This, whenever the destination reads M4A — which covers every Apple device, most modern software and any recent car. It is lossless where MP3 is not, and it is faster. Choose MP3 when the file has to play on something old or unknown, because nothing refuses MP3.
Why is the file so much smaller than the video?
Because the picture is discarded rather than converted. In a typical recording the images are almost all of the bytes and the sound is a small remainder. Nothing is compressed to achieve that — the images are simply not carried across.