Convert AVI to MP4
Convert an AVI into an MP4 that a phone, a browser or a smart TV will play. AVI is a Microsoft container from 1992, and the files that survive are usually old camcorder footage, ripped discs or downloads from an era when DivX and Xvid were the codecs everybody used. Those codecs are the actual problem: modern devices dropped support for them long before they dropped support for the container.
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Up to 50 MB. Deleted automatically after 30 minutes.
What it does
- Re-encoded to H.264 video and AAC audio
- Reads DivX, Xvid and MJPEG payloads
- Plays on phones, browsers and smart TVs
- No watermark and no sign-up
How to use AVI to MP4
- 1
Add the AVI
Drop the file in or choose it from your computer. Up to 50 MB, with no account.
- 2
Convert
Whatever codec is inside is decoded and rewritten as H.264 video with AAC audio. Old files are often small, so this is usually quick.
- 3
Play it on anything
The MP4 works on phones, in browsers, on smart TVs and on the streaming stick that refused the original.
The container is old; the codec is the problem
AVI — Audio Video Interleave — was introduced by Microsoft in 1992 and was the default way Windows held video for the next decade. Camcorders wrote it, capture cards wrote it, and for years anything downloaded was an AVI.
What stops those files playing today is almost never the container. It is what is inside. DivX and Xvid dominated the 2000s, and when phones and televisions started decoding video in hardware, they built that hardware for H.264. A modern device is not refusing your AVI out of stubbornness; it genuinely has no decoder for the picture inside it.
AVI also predates a great deal that later formats take for granted. It has no real answer for modern audio, variable frame rates, or subtitles as a track rather than as pixels burned into the image.
How it works
The video is decoded, whatever codec produced it, and written into an MP4 with H.264 video and AAC audio. That is a full re-encode, which costs a little quality and is the only way to produce a file that today's hardware decoders can actually use.
Old AVI footage is usually standard definition, which means two useful things: the conversion is quick, and H.264 has more than enough room to reproduce the picture faithfully. The visible difference between the original and the result is generally smaller than the difference between the original and your memory of it.
Before you convert an archive
If you have a folder of these, convert the ones you want to watch and keep the originals. Storage is cheap, the AVI files are usually small by modern standards, and an original recording is the one thing that cannot be recreated later from anything else.
Audio is often the part that surprises people
The video codec gets the attention, but AVI's audio handling is where old files most often behave strangely. An AVI can carry MP3 audio, uncompressed PCM, or AC-3, and it has no proper mechanism for describing variable-bitrate audio. The familiar symptom is a file whose sound drifts steadily out of step with the picture, getting worse the longer it runs.
Re-encoding fixes that as a side effect, because the audio is decoded and rewritten against the video's own timing rather than trusting what the container claimed. If you have an old recording where the voices lag behind the mouths by the end, converting it is very often the whole fix — and the reason is worth knowing, because it is not obvious that a format problem could produce a symptom that looks so much like a damaged recording.
Examples
Camcorder footage from a hard drive
The archetypal case. Tape and early hard-disk camcorders wrote AVI, and those files now sit in folders that nothing on a modern phone or TV will open.
A downloaded film that will not cast
Xvid inside AVI was the standard for years. A Chromecast, a smart TV and a browser will all refuse it, and all three accept the same content as H.264 in MP4.
Frequently asked questions
Why has my AVI stopped playing?
Almost certainly because of the codec inside it rather than the container. AVI files from the 2000s usually hold DivX or Xvid video, and hardware decoders in phones, televisions and browsers were built for H.264 and never included those. The file has not degraded; the world moved to different codecs and left it behind.
Will the picture look worse?
It is re-encoded, so strictly yes, but the practical answer is usually no. Most surviving AVI footage was recorded at standard definition on consumer equipment, and H.264 at a sensible setting reproduces that comfortably. What you notice is that it plays at all.
Why is AVI still around after thirty years?
Because it was the default on Windows for a decade and hardware wrote it directly. That combination produced an enormous number of files, and files outlive the software that made them. AVI is not a bad container so much as an old one, with no support for the features later formats assume, including modern audio and subtitle handling.
Can I convert a very long AVI?
There is a 50 MB upload limit here, and an old standard-definition recording of a few minutes normally fits comfortably inside it. A full-length film almost certainly will not. For something that large, a desktop tool such as HandBrake or ffmpeg is the honest recommendation, and neither costs anything.