FOURCC Codes Explained, With a Full Reference List

A FOURCC is a four-character label that tells Windows which codec compressed a video, and knowing how to read one turns an unplayable file into a solved problem.

Open an old AVI in a codec inspector and you will see something like XVID or DX50 stamped in its header.

That four-character code is how the file announces which decoder it needs.

The full reference list is further down, but there is one thing worth knowing first, because it sends a lot of people down a blind alley.

FOURCC is an AVI idea, not a universal one

Four-character codes come from Video for Windows, and they live in the header of an AVI file. That is the mechanism, and it is the only place a FOURCC in the strict sense exists.

MP4 and MKV identify their codecs differently. An MP4 uses sample entry names such as avc1 or hvc1 inside its atom structure, and an MKV uses CodecID strings such as V_MPEG4/ISO/AVC. Those are four characters long in the MP4 case and get loosely called FOURCCs, but they are a different mechanism in a different container.

If containers and codecs are new to you as a distinction, our guide on containers and codecs covers it properly.

The codes you will actually meet

The full historical registry below runs to well over a hundred entries, most of them from hardware that has not shipped since the 1990s. These are the ones that turn up in practice.

Notice how many of those are raw rather than compressed. A raw code means the file is storing uncompressed pixels, which is why an AVI marked I420 is enormous and needs no decoder at all.

Reading the code on a file you have

You do not have to guess. Three ways, depending on how much you want installed.

• Nothing to install. Drop the file into our Codec Finder, which reads it in the browser and reports the codec and container.
• The standard desktop tool. MediaInfo reports the FOURCC alongside every other stream detail.
• The whole system. X Codec Inspector lists what is registered on the machine rather than what is in one file, which is the other half of the question.

Once you know the code, the table above or the registry below tells you what decoder to go looking for.

Changing a FOURCC, and when that helps

Occasionally an AVI carries a code that does not match what is actually inside it, usually because it was written by software taking liberties. The file will then refuse to play even though you have the right decoder installed.

The AVI FourCC Code Changer rewrites the code in the header without touching the video itself, which fixes exactly that mismatch. The classic case is an AVI labelled DX50 that plays once relabelled XVID, since Xvid and DivX are close enough for one decoder to handle both.

It only works on AVI. If the file is anything else, the fix is a decoder rather than a relabel, and the K-Lite Codec Pack covers most of what an older file is likely to want.

The full registry

This is the historical list of registered compressor codes. Most of it is of archival interest rather than practical use, which is exactly why it is worth keeping - these are the codes attached to files nobody can open any more.

Codes used for DIB compression

A DIB is a device-independent bitmap, the uncompressed image format Windows uses internally. These codes appear where a compression method is applied to one.

Quick questions

Read the code first, and only reach for a relabelling tool once you know the file is an AVI carrying the wrong one.

Download MediaInfo to read the codes on your own files, or browse more inspection tools under Codec Identifiers.

The decoders themselves sit in the Video Codecs section, and FFmpeg handles almost anything on this page from the command line.