Convert MP4 to MP3
Pulling the audio out of a video is not really a conversion of the video at all — the picture is dropped and only the soundtrack is re-encoded. That is why a 36 MB clip becomes a 300 KB MP3 in a fraction of a second, while converting the same clip to another video format takes seconds. If you want the sound of something, this is the cheapest thing you can ask for.
Use this without the search next time. Prathom Workbench puts Prathom's tools in your toolbar.
Add to Chrome — freeDrop your MP4 file here, or click to browse
Up to 50 MB. Deleted automatically after 30 minutes.
What it does
- The video stream is discarded, not re-encoded
- Audio re-encoded to MP3 at a high variable-bitrate setting
- Typically finishes in well under a second
How to use MP4 to MP3
- 1
Upload the MP4
Any MP4 with sound. A file with no audio track will produce nothing, because there is nothing to extract.
- 2
The picture is dropped
Only the audio stream is read. The video is not decoded at all, which is where nearly all of the speed comes from.
- 3
Check the length, not the size
A large drop in file size is expected and correct. What matters is that the MP3 runs as long as the video did.
How it works
The container is opened and only its audio stream is read. The video stream is not decoded, not re-encoded and not examined — it is simply not part of the output. The audio is then encoded as MP3 at a high variable-bitrate setting and written on its own.
That asymmetry is the whole story of this conversion. Video is expensive because there are millions of pixels per second to process; audio is cheap because there are a few thousand samples. Dropping one and keeping the other is close to free.
What you get
A file that plays in anything, is small enough to keep on a phone, and runs exactly as long as the video did. For lectures, interviews, podcasts recorded to video, and music from a performance clip, this is usually the format you actually wanted in the first place.
What you give up
The picture, obviously — and there is no way back. An MP3 made from a video does not contain a compressed version of the video; it contains none of it.
You also take one more lossy pass on the audio. The soundtrack inside an MP4 is already compressed, and MP3 compresses it again. At the setting used here that is not audible in ordinary listening, but it is real, and it is why a file that will be edited should be extracted losslessly instead.
When to choose something else
WAV or FLAC if the audio is going into an editor, or if it will be re-encoded again later. Both are lossless, so the second pass costs nothing.
M4A if the source audio is already AAC and you want to avoid re-encoding altogether — the stream can be carried across as it is.
A file with no sound
Screen recordings, timelapses and exported animations are often made with no audio track at all, which is not visible from the file. If the conversion refuses, check the source in a player before assuming anything is broken.
Why the audio is usually AAC
An MP4 recorded by a phone, exported by an editor or downloaded from a platform almost always carries AAC audio. That matters here because AAC is lossy, so producing an MP3 is a second generation of encoding — the AAC encoder discarded what it judged inaudible, and the MP3 encoder now works from what remains and makes its own, slightly different judgments.
For speech this is inaudible and not worth a thought. For music it is a real if small cost, and the answer is to keep the MP4 rather than to worry about the setting. You can always extract again from the original; you cannot extract back out of the MP3.
Examples
A lecture recording for listening on a commute
More than ten times smaller and it plays on anything. Nothing about the audio was degraded by the video being present, so it sounds exactly as it did in the recording.
A clip with no audio track
Screen recordings are frequently made without audio and it is not obvious from the file. If the conversion refuses, this is almost always why.
Frequently asked questions
Why is this so much faster than other video conversions?
Because the video is never decoded. Converting a video to another video format means reading every frame, re-encoding it and writing it back, which is the expensive part. Extracting audio reads only the audio stream and throws the picture away without looking at it, so the work is proportional to the soundtrack rather than to the pixels. A minute of 1080p video converts to MP3 in a fraction of a second.
Will the audio quality drop?
Slightly, because MP3 is lossy and the audio inside an MP4 usually is too, so this is a second lossy pass. The setting used here is a high variable bitrate, which is transparent for speech and close to it for music at normal listening volumes. If you need no loss at all, convert to FLAC or WAV instead; both are lossless and both are much larger.
What if the video has more than one audio track?
The first one is used. Films and some recordings carry several — different languages, or a commentary — and the conversion has no way to know which you meant, so it takes the one the container lists first. If you need a specific track, extracting it needs a tool that lets you choose, not a one-click conversion.
Further reading
- Mono at 16 kHz Was a Fifth of Stereo, and at a Fixed Bitrate Nothing ChangedMaking a recording mono is the standard advice for shrinking speech audio, and whether it works depends entirely on a setting most people never touch. Set one way it saves eighty per cent; set the other way it saves nothing at all and quietly improves the quality instead.
- The Soundtrack Was a Sixth of the File the Video Came InA lecture, an interview, a podcast recorded on camera — plenty of video is kept for its sound. The picture is almost all of the file, and dropping it is the single largest saving available on any video you only listen to.
- What Each MP3 Bitrate Actually Costs, in BytesAudio bitrate is one of the few compression settings where the size is completely predictable — unlike image quality settings, where the same number produces wildly different files depending on the picture. Here is the same recording at six bitrates plus lossless, and what the predictability means for choosing one.