MP4 to MP3 Converter
Take the soundtrack out of an MP4 and save it as an MP3, without the file ever leaving your machine. If whatever you are feeding will accept AAC, the tool can also copy the original track out untouched instead.
What is actually inside an MP4
| What the audio usually is | AAC, at 128 to 256 kbps. MP4 is a container, not a codec — it holds an AAC stream the way a folder holds a file, and that stream is not an MP3 and never was. |
|---|---|
| What converting costs | One extra generation of loss. The AAC is decoded back to audio and compressed again as MP3, so the result is a copy of a copy. It is usually inaudible at 192 kbps and up, but it is not free. |
| The lossless alternative | If whatever you are feeding accepts AAC, copy the stream into an .m4a instead. That is instant, bit-identical, and typically a smaller file than the MP3 would have been. |
| Speed | Audio-only work is fast even in WebAssembly — there is no picture to decode. A few minutes of video converts in seconds, not the minutes a video re-encode would take. |
The naming is genuinely confusing and it is not your fault: MP3 is MPEG-1 Audio Layer III, a codec from 1993. MP4 is MPEG-4 Part 14, a container from 2001. One holds audio; the other holds streams of any kind. They share a lineage and almost nothing else.
Size of the result
An MP3's size comes from its bitrate and its length — nothing else. The MP4 it came from could be twenty times larger and it changes none of these numbers, because the picture is thrown away.
| Bitrate | Per minute | Per hour |
|---|---|---|
| 128 kbps | 937.5 KB | 54.9 MB |
| 192 kbps | 1.4 MB | 82.4 MB |
| 320 kbps | 2.3 MB | 137.3 MB |
Converting a different container? The MOV converter covers QuickTime and camera files, and the general video converter takes MKV, WebM and AVI as well.
Frequently asked questions
Is an MP4 just an MP3 with video attached?
No, and the similar name is a coincidence of numbering rather than a family relationship. MP4 is a container; the audio inside it is almost always AAC, a different and newer codec than MP3. Getting an MP3 out of an MP4 means re-encoding, not renaming.
Can I get the audio out of an MP4 without re-encoding?
Yes, if you can accept AAC. Leaving the format on Original copies the AAC stream into an .m4a file byte for byte — instant, lossless, and usually smaller than the MP3 would be. Only convert to MP3 when the destination will not take AAC.
Why does my MP4 have several audio tracks?
Films and TV rips carry one track per language or per mix — stereo, 5.1, commentary. The tool lists every audio stream it finds with its codec, sample rate and language tag, so you can convert them one at a time instead of getting whichever happens to be first.
How big will the MP3 be?
It depends only on bitrate and length, not on the size of the MP4. At 192 kbps an hour of audio is about 82 MB whether it came from a 200 MB phone clip or a 4 GB film — the picture, which is nearly all of an MP4's size, is discarded.
Is there a file size limit?
Files up to 200.0 MB are accepted. The ceiling is memory: the browser holds the input while ffmpeg works on it, so a very large file can exhaust the tab before a phone or an older laptop finishes.