A recorded lecture, a meeting saved to disk, an interview filmed on a phone, a rehearsal from your own camera. In many videos the picture adds little and the sound is what you need: on headphones during a commute, in a podcast app, in a transcription tool or on a USB stick for the car. An MP3 file takes about 1.4 MB per minute at our settings and plays on almost any device with a speaker, including older car stereos that do not understand MP4 at all.
What happens to the video during conversion
The picture and any subtitle tracks are discarded, only one audio track is decoded and encoded to MP3. The settings are fixed:
- Variable bitrate (VBR). The encoder spends more bits on complex passages and fewer on silence or plain speech. The average is around 190 kbps, typically between 170 and 210 kbps. For speech the file is often smaller.
- Sample rate stays as it was (MP4 audio is almost always 44.1 or 48 kHz, both valid for MP3).
- Surround sound is mixed down to stereo, because MP3 carries at most two channels.
- Tags are copied. Title, artist or comment stored in the MP4 end up in the ID3 tag of the MP3. The video thumbnail is not used as cover art.
- Volume is not changed. There is no normalisation, so a quiet recording stays quiet.
If the MP4 contains several audio tracks (two languages, a commentary track), our converter picks the one with the most channels, and when they are equal, the first one. You cannot choose the track in our converter.
Will the MP3 sound worse than the video?
The audio in an MP4 is nearly always already compressed, usually as AAC. Converting it to MP3 is a second lossy encoding, so in theory some detail is lost. In practice, at around 190 kbps VBR most listeners cannot tell the result apart from the source in blind tests, and for speech the difference is irrelevant.
What conversion cannot do is add quality. If a phone recorded the sound as AAC at 128 kbps, the MP3 at 190 kbps will be larger than the original audio track, not better. Do not be surprised when the MP3 is bigger than the audio part of the video.
Common problems and solutions
Conversion fails with a screen recording
Screen recordings made with the microphone and system sound turned off contain no audio track at all. There is nothing to extract, so the conversion ends with an error. Play the video with sound first to check.
The MP3 has the wrong language or the commentary
See above: the track with the most channels wins. If you need a specific track, open the video in Audacity, which asks which audio stream to import, and export that one as MP3.
The video is larger than 100 MB
Phone video at 1080p easily takes 60 to 130 MB per minute, so longer clips will not fit the free limit. A screen recording of a lecture is usually much smaller per minute. For long recordings, extract the audio locally (see below) or cut the video into parts.
Old car stereo shows a wrong duration
Some very old players estimate the length of a VBR file incorrectly. The file plays fine, only the time display is off. If it bothers you, convert the file locally with a constant bitrate (CBR), for example 192 kbps in the MP3 export of Audacity.
Other ways to get audio from MP4
- VLC (Windows, macOS, Linux): Media → Convert / Save, add the file, choose the profile “Audio - MP3”.
- Audacity opens MP4 once its optional import library is installed, and lets you trim silence and raise the volume before export.
- Meeting software often saves a separate audio-only M4A file next to the local recording. Check the recording folder before converting.
Our converter makes sense when you do not want to install anything, work on a phone or a borrowed computer, or have several clips at once: you can upload up to 10 files together and download the results as a ZIP. Process only recordings you made yourself or have the right to use.
MP4 and MP3 at a glance
| MP4 | MP3 | |
|---|---|---|
| Type | Container for video, audio, subtitles | Audio codec and file format |
| Standard | ISO/IEC 14496-14 (2003), derived from QuickTime | ISO/IEC 11172-3 (1993), MPEG-1 Audio Layer III |
| Typical audio | AAC, 2 to 6 channels | MP3, mono or stereo, up to 320 kbps |
| Licensing | Depends on the codecs inside | Patents expired, licensing ended 23 April 2017 |
MP3 was developed largely at Fraunhofer IIS in Erlangen from the late 1980s. More detail on both formats is in the Library of Congress format descriptions for MP3 and MP4. Working with uncompressed recordings instead? See WAV to MP3. For iPhone videos that will not play, try MOV to MP4.