What is inside an MP4, and what ends up in the WAV
An MP4 is a container. It holds a video track and one or more audio tracks, and in almost every file you will meet, the audio track is AAC. Phone videos, screen recordings, Zoom local recordings, lecture captures and clips exported from editing software all follow this pattern.
The converter opens the MP4, decodes the AAC audio into raw samples and writes those samples as a 16-bit PCM WAV. The video track is dropped. The output keeps the original file name with a .wav extension, and a Download button saves it to your device.
One thing to be clear about: AAC is lossy, and decoding it to WAV does not bring back anything the AAC encoder discarded when the video was made. What you get is an exact decode of the audio that is in the MP4, with no further loss added. That is still the right starting point for editing, because every later cut and save stays lossless.
Why editors and speech tools prefer WAV
Audacity, DAWs such as Reaper, Logic or Ableton, and video editors import WAV without decoding anything. Scrubbing is instant, waveforms draw accurately, and saving a project does not run the audio through another lossy encoder. If you plan to trim a lecture, clean up the room noise in an interview, or pull a sound effect and some room tone out of a clip for sound design, WAV is the working format those tools expect.
Speech software has a different reason. Many recognition engines, voice analysis tools and training pipelines want a 16 kHz mono WAV and either reject other input or silently resample it. Producing that file yourself means you know exactly what the tool receives.
The same applies if you are preparing audio for a batch job. A folder of WAVs with identical sample rate and channel layout is easier to process than a mix of phone videos with different settings.
Choosing the sample rate and channels
The WAV output is always 16-bit PCM. You choose the sample rate and whether to keep the source channels or mix down to mono.
- Same as source: the safest default. Video audio is commonly 48 kHz, and keeping it avoids a resample step you may not need.
- 48 kHz: pick this when the WAV is going back onto a video timeline, since most video projects run at 48 kHz.
- 44.1 kHz: the rate used by CD audio and most music projects. Choose it if the WAV will sit next to music tracks in a DAW.
- 16 kHz: what many speech recognition and voice tools expect. The file is about a third of the size of 48 kHz, and speech loses nothing that matters.
- Mono: halves the file size. If the MP4 is one person talking to a camera or a screen recording with a single microphone, mono loses nothing you need. Keep stereo for music, ambience or anything mixed for two channels.
How big the WAV will be
WAV is uncompressed, so size depends only on duration, sample rate and channel count. At 16-bit stereo 48 kHz the file grows by roughly 11.5 MB per minute, or about 690 MB per hour. At 44.1 kHz stereo it is about 10.6 MB per minute. Switching to 16 kHz mono brings it down to under 2 MB per minute, which is around 115 MB for an hour of speech.
For a short screen recording, the WAV can turn out larger than the MP4 it came from, because the video was compressed hard and the audio no longer is. For a long phone video the WAV is usually much smaller than the video but far larger than an MP3 of the same audio would be. If you only need something small to share, the MP4 to MP3 page is the better fit.
The converter handles one file at a time, up to a practical limit of about 2 GB per file. Phones and tablets manage less because the browser has less memory to work with, so a long video is best converted on a laptop or desktop, or with the 16 kHz mono setting to keep the result manageable.
Nothing is uploaded
The converter is FFmpeg compiled to WebAssembly, running inside your browser. Your MP4 stays on your device, and nothing is stored on our side. The first time you use it, the browser downloads the conversion engine, about 32 MB, and caches it. After that it also works offline.
The finished WAV lives only in the open tab. Save it with the Download button before you reload or close the page, because reloading clears it. There is no sign-up or watermark, and you can convert as many files as you like. Only local files are accepted, so a YouTube or other link will not work; download the video first.
It works in current Chrome, Edge and Firefox, and in Safari 16 or newer, including on phones for smaller files.
If you actually need the words
If the reason for the WAV is to get a transcript, you can skip the editor. After the conversion, a Transcribe this file button sends the WAV into the transcription box further down this page. That step runs on our servers, so the audio is uploaded for it. You get a timestamped, editable transcript in 90+ languages and can export it as TXT, DOCX, PDF, SRT, VTT or CSV. It is free to try without an account.
You can also upload the MP4 directly on the MP4 to text page. Converting first only helps when the video is large and a 16 kHz mono WAV would be quicker to send.