ARX File

What are ARX files and how to open them

Are you having problems opening an ARX file or are you simply curious about its contents? We're here to explain the properties of these files and provide you with software that can open or handle your ARX files.

What is an ARX file?

ARX files have multiple uses, and Arriflex CODEX HDE Video is one of them. Read more about the other uses further down the page.

Arriflex CODEX HDE Video

Arriflex CODEX HDE Video is the High Density Encoding version of the ARRIRAW format created by ARRI in partnership with CODEX. It is used when uncompressed raw sensor data from ARRI cameras (ARRIRAW) is offloaded to storage media using CODEX Device Manager on macOS, with HDE enabled. Its purpose is to reduce file sizes significantly - typically to around 40-60 percent of the original - while preserving complete image quality and metadata.

Together with the rest of the ARRI workflow, HDE-encoded ARX files are written during the backup of footage from CODEX Compact Drives, Capture Drives, SXR or XR drives, or CFast 2.0 media when recording ARRIRAW. After offloading, these frame-sequence ARX files are ready to be processed - decoded back into ARRIRAW form, then used in postproduction just as uncompressed raw would be. ARX frame sequences are used by legacy and earlier ARRI ALEXA, SXT, XT and LF cameras, or until CODEX Device Manager version 7.4.2; newer cameras or newer versions use HDE wrapped in MXF instead.

The encoding uses a variable bitrate lossless algorithm specially optimised for Bayer-pattern raw images. When decoded, each ARX frame matches the original ARRIRAW frame bit for bit. The visible file size on some drives may appear as 0 bytes until the file copy or offload completes, because the encoded size cannot be predicted until encoding is finished.

In its header, ARX files begin with the ASCII signature "CDXA" followed by bytes indicating version or sequence, and include the string "ARRI " at offset 204. These bytes serve as internal identifiers. (Experience shows "CDXA.4Vx" at offset 0 and "ARRI" at offset 204 in typical ARX files.)

How to open ARX files

Important: Different programs may use files with the ARX file extension for different purposes, so unless you are sure which format your ARX file is, you may need to try a few different programs.

While we have not verified the app ourselves yet, our users have suggested a single ARX opener which you will find listed below.

Last updated: August 20, 2026

All known file formats using extension .ARX

While Arriflex CODEX HDE Video is a popular type of ARX-file, we know of 2 different uses of the .ARX file extension. Different software may use files with the same extension for different types of data.

ARX Compressed Archive

We know that one ARX format is ARX Compressed Archive. We have not yet analyzed in detail what these files contain and what they are used for. We're working on it.

Various apps that use files with this extension

These apps are known to open certain types of ARX files. Remember, different programs may use ARX files for different purposes, so you may need to try out a few of them to be able to open your specific file.

Help us help others

File.org helps thousands of users every day, and we would love to hear from you if you have additional information about ARX file formats, example files, or compatible programs. Please use the links below or email us at submit@file.org to discuss further.