Image MIME Reference
JPEG-XS-Codestream
JPEG XS Codestream
image/jxsc
VS
T.38 Fax over IP (FoIP)
image/t38
T.38
A complete technical comparison of JPEG XS Codestream and T.38 Fax over IP (FoIP) — covering compression, feature support, browser compatibility, magic bytes, and when to choose each format.
Equal browser support
Feature Support
| Feature | JPEG-XS-Codestream | T.38 |
|---|---|---|
| Transparency (Alpha) | Yes | ✕ No |
| Animation Support | ✕ No | ✕ No |
| Progressive Loading | ✕ No | ✕ No |
| HDR Support | Yes | ✕ No |
| EXIF Metadata | ✕ No | ✕ No |
| ICC Color Profile | ✕ No | ✕ No |
JPEG XS Codestream
image/jxsc
Extension
.jxsc.jxs
Container
None (Raw Codestream)
Compression
Lossy (Visually Lossless) / Mathematically Lossless
Algorithm
JPEG XS (ISO/IEC 21122-1)
Color Depth
8-bit, 10-bit, 12-bit, 14-bit, 16-bit
Developed by
Joint Photographic Experts Group (JPEG) / intoPIX
Released
2019
Magic Bytes
FF 10
T.38 Fax over IP (FoIP)
image/t38
Extension
.t38
Container
UDPTL or TCP (Network Transport)
Compression
Lossless (MH, MR, MMR / T.4, T.6)
Algorithm
MH (Modified Huffman)MR (Modified Read)MMR (Modified Modified Read)
Color Depth
1-bit (Monochrome B&W)
Developed by
ITU-T (International Telecommunication Union)
Released
1998
Magic Bytes
None (Network Stream)
Browser Support Comparison
| Browser | JPEG-XS-Codestream | T.38 |
|---|---|---|
Chrome
|
✕ | ✕ |
Firefox
|
✕ | ✕ |
Safari
|
✕ | ✕ |
Edge
|
✕ | ✕ |
IE (Legacy)
|
✕ | ✕ |
JPEG-XS-Codestream
JPEG-XS-Codestream Strengths
- Eliminates container overhead, maximizing parsing speed and minimizing latency to fractions of a millisecond
- Highly optimized for direct hardware implementation in FPGAs and ASICs
- Perfect for continuous data streaming over IP networks without needing to establish file headers
Limitations
- Lacks standard container metadata (EXIF, XMP, ICC profiles), meaning color space and orientation data must be handled externally or out-of-band
- Zero support in web browsers or standard consumer operating systems
- Often requires specialized broadcast hardware or custom software libraries to decode
T.38
T.38 Strengths
- Designed specifically to overcome the timing and packet-loss issues that plague traditional fax over standard VoIP audio codecs (like G.711)
- Reduces bandwidth requirements by transmitting fax protocol data rather than uncompressed audio tones
- Universally supported by enterprise SIP trunks and Session Border Controllers (SBCs) for FoIP
Limitations
- Not an actual image file format, causing confusion due to its 'image/' MIME classification
- Extremely complex to implement correctly over lossy UDP networks (relies on UDPTL redundancy mechanisms)
- Zero support in web browsers or standard image viewing software
When to choose which format
JPEG-XS-Codestream
Use JPEG-XS-Codestream when…
- Hardware Decoding Pipelines (FPGA/ASIC)
- Live Broadcast Infrastructure
- Video over IP Transport
- Embedded Camera Systems
T.38
Use T.38 when…
- Fax over IP (FoIP) Transmissions
- SIP/SDP Media Negotiation
- VoIP Gateways and PBX Systems
- Enterprise Fax Servers