MP4 to MP3 Converter
Extract the audio track from an MP4 video and save it as MP3 — without uploading the video anywhere. Useful for music videos, podcast video recordings, lecture captures, voice memos shared as video, and anything where you want just the sound. Runs entirely in your browser using your device's built-in audio decoder.
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Stays on your device
Your audio is decoded into your browser's memory by the Web Audio API, re-encoded by a JavaScript library running in the same tab, and the result goes straight to your downloads. No upload, no log, no third party. Sensitive recordings, voice memos, copyrighted tracks — none of it leaves your machine.
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MP4 → MP3 done right
Your browser pulls the AAC audio track out of the MP4 container, decodes it to raw PCM samples, and encodes them to MP3 using lamejs. The video frames are never decoded — only the audio. That's why a 200MB video can become an 8MB MP3 in seconds rather than minutes: we never touch the expensive part.
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Quality control
Pick the MP3 bitrate that matches your use case — 128 kbps for podcasts and voice (smaller files), 192 kbps for music (our default, near-CD quality), or 320 kbps for archival (best fidelity, largest files).
Frequently asked questions
Does my audio ever leave my device?
No. The conversion runs entirely in your browser. We decode your file using the Web Audio API and re-encode it using a JavaScript encoder library, all in your browser tab. Open DevTools while you convert — you'll see zero traffic carrying your audio.
Is there a file size limit?
No fixed limit from us. The real ceiling is your device's memory: decoded audio sits in RAM as raw PCM, which is roughly 10 MB per minute of stereo audio at 44.1 kHz. A typical 5-minute song needs about 50 MB of working memory — fine on any modern phone or laptop. Hour-long podcasts may struggle on older devices.
Will the conversion change the audio quality?
MP3 is a lossy format, so encoding to MP3 always involves some quality loss compared to the source. At 192 kbps (our default), the difference is inaudible to most listeners on most playback hardware. WAV is lossless — if you're converting TO WAV, the output is bit-identical to what your source decoded into. If you're converting FROM a lossy source (MP3, M4A), the WAV won't be higher quality than the source — it'll just be uncompressed.
How long does conversion take?
Decoding is near-instant. Encoding speed depends on output format: WAV is essentially instant (just writing bytes). MP3 takes about 1 second of compute per 10 seconds of audio on a modern laptop — so a 5-minute song encodes in roughly 30 seconds. Phones are slower; expect 2-3x longer. Progress is shown live as the encoder works.
Does this work on mobile?
Yes. Tap the drop zone to open the file picker, choose your audio file, hit Convert. The result downloads to your device's standard download location. iOS users: the file lands in the Files app under Downloads.
What about ID3 tags (artist, album, song title)?
Original ID3 tags are not preserved in v1 — the encoded file gets no metadata. The audio itself is preserved exactly. If you need to keep artist/album/title info, you'll want to re-tag the output with a tool like MP3Tag (Windows) or Kid3 (cross-platform) after converting.
Will any MP4 work?
Any MP4 that the browser can play through an <audio> or <video> tag will work here — that's effectively every MP4 you'll encounter. The audio inside is almost always AAC, which is universally supported. The only files that fail are damaged downloads, DRM-protected videos (iTunes Store rentals, Apple TV downloads), or MP4 files using a rare audio codec like Dolby AC-3 on browsers that don't support it natively. If the file plays in a normal video player, it'll convert here.
Is the quality the same as the original?
Close. The conversion takes the AAC audio out of the MP4, decodes it to uncompressed PCM, then re-encodes to MP3 at your chosen bitrate (default 192 kbps — close to transparent for most listeners). At 320 kbps the output is indistinguishable from the source on most equipment. Going from AAC → PCM → MP3 is technically two lossy steps, but the perceptual difference is small. If you want lossless, convert to WAV instead.
What about the video — is it just thrown away?
Yes. The video frames are never decoded; we ask the browser for just the audio track. This is why large MP4s convert quickly — we skip the expensive part. A 200MB 1080p video typically becomes a 5–10MB MP3 in well under a minute on a normal laptop.
Are there file size limits?
Soft limit around 500MB on a modern laptop, 200MB on a phone. Above that the browser may run out of memory reading the file. If you hit a limit, compress or trim the video first (we'll add a trimmer in a future update). Conversion time scales roughly with audio length, not video resolution — a 4K video and a 480p video of the same length take roughly the same time to extract audio from.
Why does this work entirely in the browser?
Modern browsers include native AAC decoders (used for <video> playback), so we don't ship a 30MB ffmpeg WebAssembly binary. We hand the MP4 to the browser's Web Audio API, get raw audio samples back, then encode to MP3 using a small JavaScript library (lamejs, ~50KB). Total payload is tiny. Other online tools that ship full ffmpeg.wasm work too, but the initial download is huge and the conversion is no faster.
What about MOV files (Apple QuickTime)?
MOV is structurally very similar to MP4 — Apple's container format that became the basis for MP4. Most browsers will decode MOV audio the same way. If you have a .mov file, rename it to .mp4 and try it here, or drop it directly and we'll attempt the conversion. We'll likely add a dedicated MOV → MP3 page after watching how this one performs.
Can I use this for YouTube videos?
Not directly — YouTube doesn't let you download the MP4 file. You'd need a video downloader first (we have tools for some platforms under /video/). Once you have the MP4 saved locally, drop it here.