How extracting audio from a video works
An MP4 or MOV file is a container that holds separate streams: one for the picture and one (or more) for the sound. To get an MP3, the tool reads only the sound stream, decodes it to raw audio samples, and encodes those samples again as MP3, M4A or WAV. The picture is never decoded, which is why this is much faster than converting the video itself.
MP3 encoding uses a WebAssembly build of LAME, the open-source MP3 encoder used by many audio programs. M4A uses your browser’s AAC encoder, and WAV needs no encoder at all. Everything runs on your device; the video is not uploaded.
Choosing a format and bitrate
| Format | Typical use | Size for 1 minute (stereo) |
|---|---|---|
| MP3 128 kbps | Speech, podcasts, audiobooks | about 0.96 MB |
| MP3 192 kbps | Music, general use | about 1.44 MB |
| MP3 320 kbps | Highest MP3 quality | about 2.4 MB |
| M4A (AAC) copy | Exact original sound from most MP4s | same as the original track |
| WAV 16-bit 48 kHz | Editing, mastering, transcription tools | about 11.5 MB |
The sizes follow directly from the bitrate:
For WAV the “bitrate” is fixed by the raw samples:
Worked examples
A 4-minute music video to MP3 at 192 kbps. 192,000 × 240 ÷ 8 = 5,760,000 bytes, so about 5.8 MB. At 128 kbps it would be about 3.8 MB.
A 50-minute lecture to mono MP3. At 128 kbps: 128,000 × 3,000 ÷ 8 = 48,000,000 bytes, about 48 MB. Speech in mono stays clear at 64 kbps, which halves that to about 24 MB.
The same lecture as WAV. 48,000 × 1 channel × 2 bytes × 3,000 s = 288 MB. That is why WAV is best kept for editing, not sharing.
When M4A is the smarter choice
Almost every MP4 from a phone, camera or screen recorder stores its sound as AAC. Choose M4A and the tool copies that AAC stream straight into a new file, with no decoding or re-encoding. It is nearly instant and the sound is bit-for-bit identical to the video’s. Converting to MP3 always means one extra round of lossy compression, so a higher bitrate cannot add back detail that was never there.
M4A plays on iPhone, Android, Windows, macOS and in most music apps. Pick MP3 when you need the widest compatibility, such as old car stereos or some DJ software.
Tips and edge cases
- Choose a bitrate at or below the source. If the video’s audio is 128 kbps AAC, an MP3 at 320 kbps is just a bigger file. The file details line shows the codecs inside your video.
- Videos without sound (some screen recordings and GIF-style clips) are flagged before conversion.
- Surround sound (5.1) is mixed down to stereo for MP3 and M4A.
- Batches: add many videos at once. They are converted one after another, and you can download them all as a ZIP.
- Only part of the audio? Convert first, then cut it with the Audio Trimmer, which also adds fade-in and fade-out. To change an existing audio file’s format, use the Audio Converter.
- Need a smaller video instead? The Video Compressor keeps the picture and shrinks the file.
Use your own files
This converter is for videos you made or have permission to use: lectures, interviews, your own music practice, family videos and work recordings. It does not download anything from YouTube, TikTok or other sites, and it never sends your files anywhere.
Browser support
Extracting audio works in current Chrome, Edge, Firefox, Opera and Safari, on computers and phones. Browsers without the WebCodecs audio engine decode the sound with the Web Audio API instead, which uses more memory for very long videos.