Convert AVI to MP3
Pull the soundtrack out of an AVI as an MP3. The picture is discarded rather than converted, which is why this finishes in seconds on a file that would take minutes to convert as video. AVI has one quirk worth knowing before you start: its audio is very often already an MP3 sitting inside the container, so what you are doing is frequently a re-encode of something that was already the format you asked for.
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Up to 50 MB. Deleted automatically after 30 minutes.
What it does
- The video stream is discarded, not re-encoded
- Reads MP3, PCM and AC-3 audio from old files
- Corrects audio drift as a side effect
- No watermark and no sign-up
How to use AVI to MP3
- 1
Add the AVI
Drop the file in or choose it from your computer, up to 50 MB. Old AVI files are usually well within that.
- 2
Convert
The video is dropped and whatever audio the container holds — MP3, PCM or AC-3 — is decoded and re-encoded to MP3.
- 3
Keep the sound
The result plays on anything, and is a fraction of the size of the video it came from.
The audio is often the better half
AVI files that survive from the 1990s and 2000s tend to look their age. They were compressed for the hard drives and connections of the time, usually at standard definition, often with DivX or Xvid making visible compromises.
The audio frequently held up much better. Storage pressure fell mostly on the picture, because that is where the bytes are, and MP3 at the settings people used was reasonable then and is reasonable now. It is common to open an old AVI, find the video unwatchable by modern habits, and find the sound perfectly acceptable.
That makes extraction a genuinely useful thing to do with an archive rather than a compromise. You are usually keeping the part that aged well.
How it works
The video stream is discarded and the audio track is decoded and re-encoded to MP3 at a high variable-bitrate setting. Whatever the container held — MP3, raw PCM, or AC-3 from a disc rip — is read the same way.
Because the frames are never processed, this is fast, and the output is small.
The sync problem, and why extracting fixes it
AVI predates variable-bitrate audio as a normal thing, and it has no proper way to describe one. Its timing model assumes the audio arrives at a constant rate. An enormous amount of variable-bitrate MP3 was put into AVI files anyway, and the result is the familiar symptom: sound and picture in step at the beginning and visibly apart by the end.
Extracting the audio disposes of the problem entirely, because there is no longer a video for it to drift against. The MP3 that comes out is correctly timed against itself. This is the one case where taking the sound out of a video is a repair rather than a reduction.
If the audio is PCM
Camcorders and capture cards often wrote uncompressed audio into AVI, which is worth noticing: it means the file has never been through a lossy encoder. The MP3 you get is a first-generation encode of an original recording, which is as good as an MP3 gets. Those files are also large for their length, so the size reduction is dramatic.
Examples
Music from an old downloaded video
AVI files of live music from the file-sharing era are common, and the audio is usually the only part still worth having at that picture quality.
Narration from a camcorder recording
Camcorder footage where somebody is talking over it — the commentary survives long after anyone wants to watch standard-definition video of a beach.
Frequently asked questions
If the audio inside is already MP3, why re-encode it?
Because extracting it untouched and re-encoding it are different operations, and this does the second. Copying the existing MP3 stream out is possible and lossless, and a desktop tool such as ffmpeg will do it in one command. Re-encoding costs a small amount of quality and produces a file with clean, consistent timing, which is often the more useful outcome for an old AVI.
Why does my AVI's sound drift out of sync?
Because AVI has no proper mechanism for variable-bitrate audio, and a great deal of the audio put into it was variable-bitrate MP3 regardless. The container assumes a constant rate, the actual rate wanders, and the error accumulates — which is why the problem is invisible at the start of a file and obvious by the end. Extracting the audio removes the video it was drifting against.
What audio might be inside an AVI?
Most often MP3, frequently uncompressed PCM on files from camcorders and capture cards, and sometimes AC-3 on anything ripped from a disc. All three are read here. PCM is the interesting case: it is uncompressed, so it is the one source where encoding to MP3 is a first lossy pass rather than a second.
Is the quality worth having?
Usually more than the video is. Audio from the AVI era was often encoded at settings that hold up well, while the video was compressed hard for the storage and bandwidth of the time. It is common for a file to look dated and sound entirely fine, which is exactly the case where extracting the audio is the right thing to do with it.