JPEG-XS-(HEIF)

JPEG XS Image (HEIF Container)

image/jxsi Released 2019 · by Joint Photographic Experts Group (JPEG)

The image/jxsi MIME type represents a single JPEG XS (Extra Speed) image, or a static collection of images, encapsulated within a High Efficiency Image File Format (HEIF) container. It merges the ultra-low latency, low-complexity wavelet compression of JPEG XS with the robust metadata, color profiling, and object-based architecture of the ISOBMFF standard.

Professional & Video Production Transparency ✦ HDR Production Ready

Technical Specifications

MIME Type

image/jxsi

Extensions

.jxsi.jxs.hif

Container

HEIF / ISOBMFF (ISO/IEC 23008-12)

Compression

Lossy (Visually Lossless) & Mathematically Lossless

Algorithms

JPEG XS (ISO/IEC 21122-1)

Color Depth

8-bit, 10-bit, 12-bit, 14-bit, 16-bit

Metadata

EXIF XMP ICC

Capabilities

Transparency

Animation

Progressive Loading

Alpha Channel

HDR Support

Official Specification

Aliases: image/heif

Magic Bytes & HTTP Headers

File Signature (Magic Bytes)

XX XX XX XX 66 74 79 70 6A 78 73 69

ASCII: ....ftypjxsi

HTTP Headers

Content-Type: image/jxsi

HTML Accept Attribute

accept="image/jxsi, .jxsi, .hif"

Browser Support Matrix

Browser	Status	Min Version
Chrome	Not Supported	—
Firefox	Not Supported	—
Safari	Not Supported	—
Edge	Not Supported	—
Internet Explorer	Not Supported	Legacy

Advantages & Limitations

Advantages

Provides sub-millisecond encoding and decoding latency while retaining visually lossless quality
Brings the extensive metadata, EXIF, XMP, and color-profiling capabilities of the HEIF container to JPEG XS
Allows grouping of multiple high-quality JPEG XS frames into a single collection file

Limitations

Zero web browser compatibility, limiting it entirely to professional and industrial hardware workflows
Extremely niche adoption compared to standard HEVC-based HEIC or raw JPEG XS codestreams
Requires custom parsing logic to extract the JPEG XS codestream from the HEIF boxes

Developer Code Snippets

import magic
print(magic.from_file('photo.jxsi', mime=True)) # May default to generic 'image/heif' or 'application/octet-stream'

const FileType = require('file-type');
const type = await FileType.fromFile('photo.jxsi');
console.log(type?.mime); // Parsers may fail to recognize the specific 'jxsi' HEIF brand

import "net/http"
// Custom ISOBMFF box parsing is required to read the 'jxsi' brand inside the ftyp box.

$mime = mime_content_type('photo.jxsi');
echo $mime; // Standard environments typically map this to application/octet-stream

File Detection Steps

How to programmatically detect a image/jxsi file by reading its raw bytes:

1 Check bytes 4-7 for the standard ISOBMFF 'ftyp' box identifier
2 Verify the major brand string at bytes 8-11 is exactly 'jxsi' (6A 78 73 69)

Software Support

i

intoPIX FastTICO-XS

ImageMagick

Conversion Tools

Share & Embed

Markdown Badge

[![JPEG-XS-(HEIF) Format](https://freewebptojpg.com/mime/image/jpeg-xs-(heif)/badge.svg)](https://freewebptojpg.com/mime/image/jpeg-xs-(heif))

Interactive iframe Widget

<iframe src="https://freewebptojpg.com/mime/image/jpeg-xs-(heif)/embed" width="100%" height="280" style="border:1px solid #cbd5e1;border-radius:8px;" title="JPEG-XS-(HEIF) Specs"></iframe>

JSON API

All data on this page is available as a free, open JSON API. Use it in your project, documentation, or tooling.

GET https://freewebptojpg.com/mime/image/jpeg-xs-(heif).json Open JSON

Free to use

No auth required

CORS enabled

Use from any domain

Cached 24h

Cache-Control headers set

Frequently Asked Questions

What is the difference between image/jxs and image/jxsi?

While image/jxs is the broader MIME type for JPEG XS files (often encapsulating standard codestreams), image/jxsi specifically denotes that the JPEG XS image data is housed inside a High Efficiency Image File Format (HEIF) container, granting it advanced metadata and collection features.

What is the magic byte for an image/jxsi file?

Because it uses the HEIF/ISOBMFF container structure, an image/jxsi file begins with a 4-byte box size, followed by the 'ftyp' identifier, and the major brand 'jxsi'. The hex sequence is XX XX XX XX 66 74 79 70 6A 78 73 69.

Is image/jxsi supported in web browsers?

No. JPEG XS is engineered for ultra-low latency hardware decoding in live broadcast (like SMPTE ST 2110) and medical imaging. It is completely unsupported in consumer web browsers.