AVI to MP4 Converter

Convert AVI video files to modern MP4 format with H.264 encoding.

Tested tool guide Tested browser tools Checked August 16, 2026

What AVI to MP4 Converter does and how it behaves

AVI is a 1990s-era container that can wrap almost any video codec, some of which modern browsers and phones can no longer decode. This tool reads an AVI file in your browser, decodes its video and audio tracks, and re-encodes the video as H.264 inside an MP4 container, with audio typically becoming AAC. It's a real transcode, not a rename: the output has a different exact bitrate and file size, not a byte-for-byte repackaging. The most common surprise is that an AVI already holding H.264 video still gets fully re-encoded, so quality can drop slightly even though the codec name doesn't change.

How the result is produced

Decode then re-encode, not just rewrap

AVI can hold many video codecs - MJPEG, DV, Xvid/DivX, Cinepak, or even uncompressed frames - none of which MP4 players expect by default. The tool demuxes the AVI, decodes each video frame and the audio track, then encodes the video as H.264 and the audio as AAC before muxing both into a new MP4 container, so output quality depends on the encoder's chosen bitrate.

Runs in the browser, not on a server

Decoding and encoding happen locally using the browser's own video processing, so the file is never uploaded. This also means speed and reliability depend on your device and browser: an AVI codec your browser can't decode (some older MJPEG or DV variants) will fail to convert, and large files can be slow or memory-heavy since there's no server-side hardware encoder involved.

Good uses

Turning old camcorder or DV AVI footage into a file that plays on a phone, smart TV, or browser without a plugin
Preparing AVI footage for upload to a platform (social media, ad system, LMS) that only accepts MP4/H.264
Shrinking large uncompressed or MJPEG AVI files into smaller H.264 MP4s for storage or sharing

Limits and checks

The conversion is lossy: re-encoding always discards some quality, and an AVI that already contains compressed video (Xvid, DivX, existing H.264) gets compressed a second time, which can compound artifacts.
If the original AVI's audio codec isn't one your browser can decode, the audio track can fail or come through silent in the output MP4 - play back the result and check for sound before deleting the source.
File size doesn't always drop. An AVI already holding efficient H.264 video can end up close to its original size after re-encoding, while an old uncompressed or MJPEG AVI can shrink by an order of magnitude or more.

Common questions

Will the converted MP4 look identical to the original AVI?

No. Any re-encode changes pixel data, even at high quality settings, because H.264 is a lossy codec. Differences are usually invisible at normal viewing sizes, but pixel-level comparison will show them, and a low target bitrate will produce visible compression artifacts.

Why did the output have no sound?

Most likely the AVI's audio track uses a codec the browser can't decode, such as certain ADPCM or DV audio variants, so the tool couldn't carry it into the MP4. Try the source file in a desktop media player first to confirm it actually has audio, then check for a browser update.

References and verification

The behavioral notes were checked against the browser implementation. Standards and primary references below define the relevant format, formula, or platform behavior.