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ToolPika

Audio Converter

Choose audio or video files, pick MP3 or WAV and press Convert. Everything happens on your device, so your files are never uploaded.

Convert to

192 kbps is hard to tell from the original for most music. 128 is enough for speech; 320 is the highest MP3 quality.

Runs in your browser. Nothing you enter is sent to a server.

How it works

Your browser reads the file and decodes its audio track to raw samples. Those samples are then written again as MP3 or WAV by an encoder that runs in a background thread on your device, so the page stays responsive and you see the progress of each file. Files are converted one after another to keep memory use low.

The output is always 44.1 kHz, the sampling rate of an audio CD, at 16 bits. Audio recorded at another rate, such as the 48 kHz used by most video, is resampled. Surround sound is mixed down to stereo.

MP3 or WAV?

MP3 WAV
Compression Lossy: removes detail that is hard to hear None: every sample is stored
Size of one minute in stereo 1.4 MB at 192 kbps 10.6 MB
Plays on Practically everything Practically everything
Use it for Listening, sharing, phones, podcasts Editing, music production, devices that require it

How large will the file be?

An MP3’s size depends only on its length and bitrate, not on what it contains:

size in MB ≈ minutes × kbps × 0.0075

Bitrate One minute A 4-minute song A 1-hour recording
128 kbps 0.96 MB 3.8 MB 57.6 MB
192 kbps 1.44 MB 5.8 MB 86.4 MB
256 kbps 1.92 MB 7.7 MB 115.2 MB
320 kbps 2.40 MB 9.6 MB 144.0 MB

A stereo WAV file takes 10.6 MB per minute, so the same 4-minute song is about 42 MB. Choosing mono halves a WAV file; for MP3 the size stays the same, but all of the bitrate goes to one channel, so speech sounds cleaner at 128 kbps.

Getting the best quality

  • Convert from the original. Each conversion to MP3 loses a little. Going from WAV or FLAC to MP3 once is fine; going MP3 → MP3 at a lower bitrate adds the losses together.
  • Do not raise the bitrate of an MP3. Converting a 128 kbps file to 320 kbps makes it larger, not better.
  • Use mono for voice. A lecture or interview recorded on one microphone carries no stereo information worth keeping.

The MP3 encoder is lamejs, a JavaScript port of LAME, used under the LGPL licence.

Frequently asked questions

How do I convert an MP4 video to MP3?

Choose the MP4 file, leave MP3 selected and press Convert. Only the audio track is read; the picture is ignored. The same works for MOV and WebM videos.

Are my files uploaded to a server?

No. Your browser decodes and encodes the audio itself, so recordings, voice notes and videos stay on your device. You can check it by disconnecting from the internet after the page has loaded; the converter keeps working.

Which MP3 quality should I choose?

192 kbps suits most music. Use 128 kbps for speech, podcasts and voice notes, where the smaller file matters more than the last bit of detail. 256 and 320 kbps are for music you want to keep at the best quality MP3 allows.

Does converting MP3 to WAV improve the sound?

No. WAV stores exactly what it is given, so the detail the MP3 already removed does not come back. Convert to WAV when a program or device requires it, not to gain quality.

Why can my file not be read?

The converter uses the audio decoders built into your browser. MP3, WAV, M4A, AAC, FLAC and MP4 work everywhere. OGG, Opus and WebM work in Chrome, Firefox and Edge, and in recent versions of Safari. WMA and protected files bought with copy protection (DRM) cannot be read.

Is there a limit on length?

Each file can be up to 200 MB. The audio is held uncompressed in memory while it is converted, which takes about 20 MB per minute, so recordings of more than an hour can fail on a phone. A computer handles several hours.

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