ARRIRAW File (.ari): What It Is and How to Open It

The basics

What is an ARI file?

ARRIRAW is the raw format of ARRI's digital cinema cameras: the ALEXA family and the AMIRA. ARRI describes it as uncompressed, unencrypted sensor data, a digital equivalent of the film negative. ALEXA cameras have offered it since the original ALEXA of 2010, which sent ARRIRAW to external recorders.

In its classic form, ARRIRAW is a sequence of .ari files: one file per frame, so a one-minute clip at 24 fps is a folder of 1,440 files. Newer cameras wrap the same data in a single MXF file per clip (MXF/ARRIRAW), and ARRI's lossless HDE encoding makes either form about 40% smaller. The image data is the same in all of them.

Like other raw formats, ARRIRAW stores exposure index, white balance and the camera look as metadata, not burned into the pixels. The colourist develops the frames later: demosaicing, white balance, colour conversion and tone mapping all happen in software.

In short

ARRIRAW is a camera original for grading and visual effects. For review and sharing, export MP4; for VFX handover, studios usually render OpenEXR frames from it.

Anatomy

What's inside an ARI file

Unlike most raw video formats, ARRIRAW's frame layout is published: ARRI documented it as SMPTE Registered Disclosure Document RDD 30, "ARRIRAW Image File Structure and Interpretation Supporting Deferred Demosaicing to a Logarithmic Encoding". An .ari file is a fixed 4,096-byte header made of ten subheaders, followed by the image data. All numbers are little-endian. Below is the layout from RDD 30 (header version 3, as written by the 12-bit ALEXA generation), with offsets in bytes; it isn't a dump of a real camera file, and the ALEXA 35's 13-bit files are newer than this document.

frame.ari (header layout from SMPTE RDD 30)

frame.ari: one ARRIRAW frame (layout from SMPTE RDD 30)

offset  bytes / section            contents
0       41 52 52 49   "ARRI"       magic number (U32 0x49525241)
4       12 34 56 78                byte order check: 0x78563412,
                                   so the file is little-endian
8       00 10 00 00                header size: 4,096 bytes
12      03 00 00 00                header version 3
16      Image Data Information     68 bytes: width (+4), height (+8),
                                   active image area, offset (+52) and
                                   size (+56) of the image data
84      Image Content Information  268 bytes: white balance (CCT,
                                   tint), exposure index, colour
                                   matrix, sharpness, saturation, CDL
352     Camera Device Information  528 bytes: camera type, serial
                                   number, shutter, frame rates,
                                   timecode, magazine serial, UMID
880     Lens Data Information      200 bytes: focus distance, focal
                                   length, aperture, lens serial, model
1080    VFX Information            184 bytes
1264    Clip Information           552 bytes: reel, scene, take,
                                   director, production
1816    Sound Information          220 bytes: external timecode, file
2036    Camera Information         84 bytes
2120    ARRI-reserved              1,976 bytes
4096    image data                 12-bit log photosite values, packed
                                   8 to every 12 bytes, row by row:
                                   GR R GR R … / B GB B GB …
(…)     optional 1D LUT            a tone curve chosen by the user

141 52 52 49
The magic number
The 32-bit value 0x49525241 stored least significant byte first, so the file starts with the letters ARRI.
212 34 56 78
Byte order
The value 0x78563412. A reader that gets this number back is reading the file in the right byte order, little-endian.
300 10 00 00 03 00 00 00
Header size and version
The header is always 4,096 bytes, and RDD 30 describes version 3. Each subheader after the root starts with the length of its defined content, and spare reserved space lets ARRI add fields without moving anything.
4Image Data Information
Size and where the pixels are
Width and height of the photosite array, the active image area, and the offset and size of the image data. Readers should use the stored offset instead of assuming the data starts at byte 4,096.
5Image Content Information
The look, as metadata
White balance as a colour temperature and a green–magenta tint, the exposure index (ISO), a colour matrix, sharpness, saturation and ASC CDL values. None of them has been applied to the image data: they're instructions for the software that develops it.
6Camera Device, Lens Data, Clip Information
Production metadata
Camera type and serial number, shutter angle, frame rates and timecode, magazine serial, a SMPTE UMID, focus distance, focal length, aperture and lens serial number, plus reel, scene, take, director and production names.
7image data
The photosites
One value per photosite, in a 12-bit approximately logarithmic encoding of the sensor's 16-bit values. A photosite that received no light has the 16-bit value 256. Values are packed tightly, 8 photosites to every 12 bytes, from the top-left photosite row by row. The top-left one is green (on a red row), so rows alternate green-red and blue-green.
8optional 1D LUT
A second payload
A file may carry a 1D lookup table after the image, for a tone curve chosen on set. Offsets in the header say where each part is.

Under the hood

Uncompressed log data, and why ARRIRAW looks flat

ARRI's sensors measure each photosite with 16-bit precision. ARRIRAW stores those values in a 12-bit, approximately logarithmic encoding that favours deep shadow detail: more of the available codes go to the dark end, fewer to the highlights. That keeps the full latitude of the sensor (14 stops and more on ALEXA cameras, 17 stops on the ALEXA 35, according to ARRI) in 1.5 bytes per photosite. The ALEXA 35 uses a 13-bit encoding.

No compression is applied, which is unusual: REDCODE RAW, Blackmagic RAW and ProRes RAW are all lossy. The cost is size. The benefit is that nothing is lost to compression and decoding is simple arithmetic, which suits visual effects work and long-term archiving.

Developed with ARRI's standard processing, the image comes out in Log C (LogC3 in ARRI Wide Gamut 3 for ALEXA and AMIRA cameras, LogC4 in ARRI Wide Gamut 4 for the ALEXA 35). A log image looks grey and low in contrast until a LUT or output transform maps it to Rec.709 or HDR. If ARRIRAW looks washed out in your software, that's the reason: set the output colour space, or apply ARRI's LUT for the camera.

There's no embedded preview image in an .ari file. Every frame has to be demosaiced to be seen, which is why ordinary image viewers can't open it even though the format is documented.

Variants

.ari frames, MXF/ARRIRAW and HDE

Variant	Files	Written by
ARRIRAW (`.ari`)	One file per frame, in a folder per clip	Earlier ALEXA models; the first ALEXA sent ARRIRAW over a T-Link cable to certified external recorders such as the Codex Onboard
MXF/ARRIRAW	One MXF file per clip, same image data	ALEXA Mini and AMIRA (to CFast 2.0 cards); exclusively on the ALEXA Mini LF and ALEXA 35; the ALEXA 265 to Codex Compact Drives
ARRIRAW HDE (`.arx`, MXF/HDE)	As above, with lossless High Density Encoding: about 60% of the original size	Never the camera. Made while offloading with Codex software (Codex Device Manager or Codex Platform) or with ARRI's ARRIRAW HDE Transcoder

The MXF mapping is published as SMPTE RDD 54 (2022), so MXF/ARRIRAW files follow the normal MXF structure described on our MXF page, with ARRIRAW frames as the picture essence. HDE is lossless: decoding an HDE file gives back exactly the original ARRIRAW data.

Keep the clip together

With .ari sequences, a clip is only complete if every frame file is there. A missing or zero-byte frame shows up as a flash or a gap in the timeline. Copy whole clip folders with a tool that verifies checksums, as ARRI and Codex recommend.

Storage

How big ARRIRAW files are

Because it's uncompressed, ARRIRAW's size depends only on the recording resolution and frame rate, not on what's in the picture. ARRI's own figures:

Camera and format	ARRIRAW	HDE
ALEXA SXT, Open Gate (3424 × 2202)	11.5 MB per frame, 996 GB per hour	6.9 MB per frame, 598 GB per hour
ALEXA LF, Open Gate (4448 × 3096)	20.9 MB per frame, 1.80 TB per hour	12.5 MB per frame, 1.08 TB per hour
16:9 2.8K, 24 fps	1.34 Gbit/s	Not given
ALEXA 65, Open Gate (6560 × 3100), 24 fps	5.89 Gbit/s	Not given

A day of shooting can fill several terabytes. HDE exists to reduce that: about 40% less storage and transfer time, with no loss.

How to

How to open and convert ARRIRAW

ARRI Reference Tool (ART): ARRI's free reference software for ARRIRAW. The GUI runs on macOS and Windows; a command-line version also runs on Linux. It reviews clips, shows and extracts metadata, applies looks and exports ProRes, OpenEXR (16- and 32-bit), 16-bit TIFF and HDE. It reads .ari, MXF/ARRIRAW and both HDE forms, and replaces the older ARRIRAW Converter for most workflows.
Grading and finishing: DaVinci Resolve, FilmLight Baselight and Daylight, and Colorfront Transkoder read ARRIRAW, including HDE. Premiere Pro, Assimilate Scratch and Autodesk Flame and Smoke read ARRIRAW too.
On-set and data management: Pomfort Silverstack, YoYotta and other offload tools copy, verify and, where supported, HDE-encode ARRIRAW.
Software developers: the ARRIRAW SDK, available to software vendors from ARRI, gives applications ARRI's own processing and look file support.

Because the colour science of the newest cameras (ALEXA 35, ALEXA 35 Xtreme and ALEXA 265, processed with ARRI's ADA-7 debayering and REVEAL Color Science) needs current software, an older application may open older ALEXA footage but not files from these cameras. Updating the application, or rendering through the current ARRI Reference Tool, fixes it.

To share footage, render ProRes or an H.264 MP4 with the camera's LUT applied. For visual effects vendors, the handover is often a sequence of EXR files in ACES or ARRI Wide Gamut, which keeps the full range of the raw data.

Troubleshooting

Common ARRIRAW problems and fixes

Symptom	Usual cause	Fix
Double-clicking an `.ari` file does nothing useful	No ordinary image viewer reads ARRIRAW.	Open the clip folder in the ARRI Reference Tool, Resolve or another listed application.
The picture is grey and flat	The frames are shown in Log C without a LUT or output transform.	Choose a Rec.709 or HDR output, or apply ARRI's LUT for the camera.
An `.arx` or MXF/HDE file won't open	The application doesn't support HDE, or is too old.	Update it, or decode the HDE back to ARRIRAW with Codex software or the ARRI Reference Tool.
ALEXA 35 or ALEXA 265 footage won't open, or looks wrong	The application predates these cameras' colour science.	Update the application, or render through the current ARRI Reference Tool.
A flash frame or gap in an `.ari` clip	A frame file is missing or damaged, often after an unverified copy.	Copy the clip again from the camera original or a verified backup.

Privacy

What the metadata in an ARRIRAW file reveals

Every .ari frame repeats a 4 KB header full of production detail, and the MXF form carries the same information. According to RDD 30 it can include:

Equipment: camera type and serial number, camera ID, magazine serial number, lens model and serial number.
Shooting data: exposure index, white balance, shutter angle, frame rate, focus distance, focal length, aperture and timecode.
Production details: reel, scene and take, and director and production names if they were entered in the camera.

That's useful in post-production and for visual effects, where lens data matters. Before releasing raw frames outside a production, check what's in them with the ARRI Reference Tool, which can extract the metadata to JSON or CSV.

Sample files

There are no sample ARRIRAW files on this page. ARRIRAW is recorded only by ARRI cameras, so the simplest test file is a short clip from an ALEXA or AMIRA.

Put it online

Have ARRIRAW files? Give them a link.

Drop an ARRIRAW file on 99helpers and it gets its own address to send to a colourist or VFX vendor instead of a transfer service. Browsers can't display ARRIRAW, so the file downloads when the link is opened; for .ari sequences, put the clip folder in a ZIP first.

Put an ARRIRAW file online

Questions

ARRIRAW files, frequently asked

What is an ARI file?

A single frame of ARRIRAW, the uncompressed raw format of ARRI's ALEXA and AMIRA cinema cameras. A clip is a folder of .ari files, one per frame.

How do I open an ARI file?

Use ARRI's free ARRI Reference Tool, or DaVinci Resolve, Baselight, Premiere Pro or another application with ARRIRAW support. Open the clip folder rather than a single frame.

Is ARRIRAW compressed?

No. ARRIRAW is uncompressed 12-bit log data (13-bit on the ALEXA 35). The optional HDE encoding packs it losslessly to about 60% of the size.

What is the difference between .ari and MXF/ARRIRAW?

Only the packaging. .ari stores each frame as its own file; MXF/ARRIRAW puts a whole clip in one MXF file. ARRI says there's no difference in image quality.

What is an .arx file?

An ARRIRAW frame encoded with ARRI's High Density Encoding (HDE), a lossless format about 40% smaller than ARRIRAW. It's created after shooting, when the camera media is offloaded, not in the camera.

How do I convert ARRIRAW to MP4 or ProRes?

Open the clips in the ARRI Reference Tool or DaVinci Resolve, apply the camera's LUT or a Rec.709 output, and export ProRes, or H.264 MP4 from Resolve.

Why does ARRIRAW look washed out?

It's shown in ARRI's Log C encoding, which keeps the full dynamic range but looks flat. Apply ARRI's LUT for the camera or choose a Rec.709 output to see normal contrast.

Is the ARRIRAW format documented?

Yes. ARRI published the .ari file structure as SMPTE RDD 30 and the MXF mapping as SMPTE RDD 54. The ALEXA 35's newer encoding and the HDE format are handled through ARRI's and Codex's software.

Related formats

Other file types explained

MXF file R3D file Blackmagic RAW file OpenEXR file TIFF file MOV file All file types

Keep going

Host an ARRIRAW file

Put ARRIRAW footage online at its own address for others to download.

Share an ARRIRAW file

Send camera originals as a link instead of through a transfer service.

Unzip files online

Check what's inside a ZIP of frame files before downloading it all.

Hosting guides

How to put different kinds of files online.

Sources

Last reviewed 27 October 2026.