MP4 to MP3

Convert MP4 video to MP3 for free — pick the range and create it in your browser, no upload.

Open the MP4, choose the section, and Nerulio decodes its audio track (usually AAC) and encodes an MP3 at 128–320 kbit/s, or a WAV. The MP4's video is not decoded, so an HEVC or AV1 MP4 works as long as the browser decodes the audio. AAC is already lossy, so pick an MP3 bitrate at or a little above the AAC bitrate: going higher only makes the file bigger, going much lower adds a second, audible loss.

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No upload · processed on this device

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AAC in, MP3 out

An MP4 usually carries AAC audio; MDN lists AAC, MP3, Opus and FLAC as audio codecs an MP4 can hold. AAC is in the WebCodecs codec registry, so Nerulio decodes it with the browser's audio decoder and hands the samples to LAME 3.100 for the MP3.

AAC to MP3 is lossy-to-lossy: the MP3 encoder has to describe sound the AAC encoder already simplified, and it adds artefacts of its own. A higher MP3 bitrate than the source restores nothing, while one well below it adds audible loss. Read the source bitrate with ffprobe before choosing.

Even when an MP4 already contains MP3 audio, it is decoded and re-encoded; Nerulio has no copy-out for audio. An MP4 with several audio tracks (languages, commentary) gives the primary one only.

AAC: Advanced Audio Coding, the usual MP4 audio codec.
Lossy-to-lossy: Re-encoding audio that was already compressed with loss; quality can only stay or drop.
Primary track: The audio track the reader selects first; other audio tracks are ignored.

Example: check the source before choosing a bitrate

A 45-minute recorded talk:

$ ffprobe -v error -select_streams a:0 -show_entries stream=codec_name,sample_rate,channels,bit_rate -of default=nw=1 talk.mp4
codec_name=aac
sample_rate=48000
channels=2
bit_rate=128000   → AAC, 128 kbit/s, 48 kHz stereo
MP3 192 kbit/s (≥ source): 192,000 × 2,700 s ÷ 8 = 64,800,000 bytes ≈ 61.8 MB in the result box

The sample rate stays 48 kHz unless you choose 44.1 kHz under Advanced. At 128 kbit/s the same talk would be 41.2 MB with a second lossy step at the same bitrate as the source.

From the MP4 to the MP3

In the MP4	In Nerulio	In the MP3
AAC (or MP3, Opus) audio track	Decoded in the browser	LAME 3.100, constant 128–320 kbit/s
H.264, HEVC or AV1 video	Discarded without decoding	—
48 or 44.1 kHz sample rate	Kept unless you pick another	Same rate
Several audio tracks	Primary track only	One track
Title, artist, chapters	Not copied	No tags

Check the result

The result should be as long as the section; listen to the first second to check the start is not clipped.
Compare the size with bitrate × seconds ÷ 8.
Listen to cymbals, sibilants and quiet reverb tails, where lossy-to-lossy artefacts show first.

Troubleshooting

Symptom	Likely cause	How to check	Fix
"This file has no audio track"	The MP4 was exported without sound, or the sound is in a separate file	ffprobe with `-select_streams a` prints nothing	There is nothing to extract from this file
A decoder error on the audio	The MP4 holds an audio codec this browser cannot decode, for example a surround codec	ffprobe shows codec_name	Use FFmpeg for this file
Voices sound swirly	Two lossy steps at a low bitrate add artefacts	Compare with the MP4 at the same moment	Use 192 kbit/s or more, or WAV
The MP3 is larger than the MP4's whole audio track	A higher MP3 bitrate than the AAC source	ffprobe bit_rate of the source	Pick the source bitrate or the next step up

Other ways to do it

Option	When it is the better choice
Keep the AAC as an .m4a	Players that accept AAC keep the original quality with no second encode; FFmpeg copies it with `-vn -c:a copy out.m4a`.
FFmpeg with `-vn -c:a libmp3lame -b:a 192k`	Batch jobs, or audio codecs the browser does not decode.

What this page does not cover

Audio is always re-encoded, even when the MP4 already holds MP3.
Only the primary audio track is used, and no tags or chapters are written.

Versions and sources

Checked in tests/media-browser.mjs in Chromium 153 and Firefox 155 with a 1920 × 1080 H.264/AAC MP4: a 4-second section at 192 kbit/s came out within 0.12 s of the requested length. MP4 audio codecs follow MDN; the codec list follows the W3C WebCodecs registry.

Official documentation used

MP4 to MP3

MP4 is the video format used by most phones, cameras and editors.

The audio track is decoded and encoded to MP3; the browser must support the audio codec inside the file.

Your file is never uploaded — it is processed inside this browser.

Video to MP3

Extract a selected audio range from supported videos to MP3 or WAV. Choose a bitrate and download the result, with processing in your browser.

How it works

Open a supported video or audio file
Choose the time range, MP3 or WAV, and audio settings
Export and listen to the beginning and end of the result

Supported formats

MP4 / WebM / MOV / MP3 / WAV / OGG / M4A → MP3 / WAV — Input decoding and output encoding depend on browser support.

What this tool does

Extract audio incrementally with selectable 96–320 kbit/s MP3 or PCM WAV.

Implementation and verified quality

advanced · ranged demux / WebCodecs / LAME WASM. Quality qualification is in progress. Pro/Flagship quality has not been established.

Before you export

Fast cut shrinks to inner keyframes. Precise mode re-encodes; codec availability varies. Temporary outputs use local browser storage when available. Compatibility recording retains its short-clip limits.

Frequently asked questions

What determines the supported size?

Actual device memory, storage and codec support. Tested examples are evidence, not a guarantee for every file.

Are my files uploaded?

This tool processes the files you open on your device without uploading them. Images you explicitly attach to community posts are uploaded separately. Optional engines and models are downloaded from third parties; those requests expose connection information such as your IP address.

Will my work be saved automatically?

No. Images and editing state stay in this tab; media output can use local temporary storage. Changing language preserves your work; reloading, closing the tab, or following a link to another page can clear it.