AVIF MIME Type

What does image/avif mean?

The image/avif media type identifies AV1 Image File Format files. AVIF stores AV1-coded images inside a HEIF container, which is itself based on the ISO Base Media File Format. It can hold a still image, a collection of images, or an image sequence.¹

AVIF supports lossy and lossless compression, transparency, animation, high dynamic range, wide color gamuts, and 8-, 10-, or 12-bit AV1 image data.² Those features make it useful for web photographs, illustrations with alpha transparency, and HDR delivery.

The usual extension is .avif. The IANA registration also lists .heif, .heifs, and .hif, but those broader HEIF extensions do not prove that the contained codec is AV1.³ Use .avif when the file conforms to AVIF and serve it as image/avif.

How can you identify an AVIF file?

IANA records no fixed magic number for image/avif.³ Like other ISO Base Media File Format files, an AVIF normally has a File Type Box near the beginning. Its brands can include avif for image items or avis for image sequences. The current specification says a file using an AVIF brand as its major brand should use .avif and image/avif.¹

That means a simplistic signature such as “bytes 4 through 7 equal ftyp” is not enough. MP4, HEIF, and other related containers can begin the same way. A reliable detector parses the box structure and checks compatible brands and image items.

Renaming a .jpg, .png, or generic .heif file to .avif does not convert it. If an application rejects a supposed AVIF, inspect the container with a format-aware tool such as avifdec or ffprobe instead of trusting the suffix alone.

Where did AVIF come from?

The Alliance for Open Media published AVIF 1.0.0 on February 19, 2019.⁴ Version 1.1.0 followed as an AOM final deliverable in April 2022, and AOM now publishes version 1.2.0 as the current specification.²⁵ IANA registered image/avif on January 28, 2021, with no deprecated aliases.³

The format reuses the AV1 codec, but adds an image-focused container model and interoperability profiles. The AVIF Baseline and Advanced profiles constrain details such as AV1 profile, bit depth, and dimensions so decoders can advertise realistic capabilities. Files outside those profiles can still be valid AVIF if they meet the general requirements.¹

How to open an image/avif file

Chrome, Edge, Firefox, Opera, and Safari display AVIF images. MDN lists support beginning with Chrome 85, Opera 71, Firefox 93, Safari 16.1, and Edge 121.⁶ Animation arrived later than still-image support in some browsers, so a current browser matters when sequences are involved.

For editing and conversion:

• Adobe Photoshop lists AVIF among its import and export formats.⁷
• GIMP can import and export still AVIF images through its HEIF plug-in. Its current documentation says animated AVIF is not supported.⁸
• avifdec and avifenc from AOMedia's libavif project provide command-line decoding and encoding.⁹

On the web, send the correct Content-Type: image/avif header. A <picture> element can provide a JPEG, PNG, or WebP fallback for older software:

<picture>
  <source srcset="photo.avif" type="image/avif">
  <img src="photo.jpg" alt="A descriptive alternative">
</picture>

AVIF support in Poly

Poly maps both the image/avif identifier and .avif filenames to its AVIF image type. Its image loader decodes AVIF through the native AVIF feature in the Rust image stack. Once decoded, Poly generates its normal set of WebP thumbnails, opens the file in the image viewer, and calculates visual embeddings for similarity and color search.

Poly extracts pixel dimensions and attempts to read EXIF from the HEIF container. Container-specific properties that are not exposed as EXIF may not appear in Poly's metadata. Plain images are not OCR'd, so words visible in an AVIF do not become full-text search terms. The visual embedding can still match the image's subject and appearance.

The Poly agent can inspect AVIF as image content. Agent and MCP reads may use a generated WebP thumbnail rather than passing the original AVIF bytes, which improves compatibility but means the agent sees the rendered picture rather than every container item or metadata box.

AVIF compared with JPEG, PNG, and WebP

No format wins every job. Encoder choice, quality settings, source content, and decode budget can matter as much as the container name.

AVIF often reaches a visual-quality target with fewer bytes than JPEG or WebP, but the result depends on the encoder, source, metric, and settings. AVIF encoding can also take more CPU time, especially at slow, high-efficiency settings. Compare outputs from the same source with the same visual-quality target before changing a production pipeline.

AVIF traditionally lacks JPEG-style scan-by-scan progressive rendering. Newer layered AVIF features can provide a coarse first layer and refinements, but decoder and encoder support for those features is newer than basic AVIF support.¹⁰

Converting AVIF safely

Choose the target according to the next step:

• Convert to PNG when you need a widely editable lossless image or alpha transparency.
• Convert to JPEG for maximum compatibility when transparency and HDR are unnecessary.
• Convert to WebP when a particular client accepts WebP but not AVIF.
• Keep the original AVIF when it contains HDR, animation, depth, or auxiliary images that a single-frame conversion would discard.

Check color management during conversion. An SDR export can clip HDR highlights, and dropping an ICC profile or CICP color information can change appearance. Animation, alpha, depth images, and metadata also need explicit handling because many converters export only the primary frame.

Is AVIF the same as HEIF or HEIC?

No. HEIF is the general container architecture. AVIF is a specific way to store AV1 images in that container. HEIC commonly refers to HEIF files containing HEVC-coded images. The containers are related, but the coded image data and decoder requirements differ.

An application that says it supports HEIF may support HEIC but not AVIF, or the reverse. Check the codec or brands inside the file rather than relying on .heif alone.