AVI to MP4 Converter
AVI is the one format here the fast path cannot read at all. Converting it downloads a fuller converter first — a one-time cost of about 30 MB for this job — and then re-encodes the video. Everything still runs on your own machine; it is only slower to start.
What to know about AVI
AVI is genuinely old
Microsoft shipped it in 1992, and what is inside a given AVI could be almost anything: DivX, Xvid, MJPEG, uncompressed. That variety is exactly why the streaming reader used by the other routes does not attempt it.
There is a size ceiling here that is not there elsewhere
The fallback engine holds the whole file in memory rather than streaming it, so a large AVI can exhaust the tab where an equally large MKV would convert fine. The tool checks the size and warns you before you wait.
The fast way out, if you can take an MKV
Converting an AVI to MKV copies the streams instead of re-encoding them, because Matroska accepts nearly any codec. It still needs the fallback engine to read the AVI, but the conversion itself finishes in seconds rather than minutes.
What MP4 carries without re-encoding
These are the video codecs a MP4 can hold in a way other software will actually open. If your AVI already contains one of them, the stream is copied across untouched and nothing is re-compressed. Anything else is re-encoded to H.264.
H.264H.265
Need something smaller rather than something different? Compress it to a target size instead — that one aims at a file size you name.
Frequently asked questions
Why is AVI slower than the other formats?
The fast streaming reader this site uses cannot open AVI at all, so this job downloads a fuller converter first — about 30 MB, once per session. Every other format on the site skips that entirely, which is why AVI is the only page that warns you before you start.
Is there a size limit for AVI specifically?
Yes, and it is much lower than elsewhere. The fallback engine holds the whole file in memory instead of streaming it, so a large AVI can exhaust the browser tab where an equally large MKV would convert fine. The tool checks the size and says so up front.
Is there a faster option?
Convert to MKV rather than MP4. Matroska accepts nearly any codec, so the streams are copied instead of re-encoded and the conversion itself finishes in seconds. It still needs the fallback engine to read the AVI, but it skips all the encoding work.
What is actually inside an AVI?
Almost anything — DivX, Xvid, MJPEG, uncompressed. Microsoft shipped the format in 1992 and it predates the conventions that make modern containers predictable. That variety is exactly why the streaming reader does not attempt it.
Will the quality change?
Yes, slightly — this path re-encodes to H.264. Given most AVI files are already old, heavily compressed DivX or Xvid, the practical difference is usually small.