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Image MIME Reference
APNG

Animated Portable Network Graphics

image/vnd.mozilla.apng
VS

FAST Search & Transfer Image

image/vnd.fst
FST-Image

A complete technical comparison of Animated Portable Network Graphics and FAST Search & Transfer Image — covering compression, feature support, browser compatibility, magic bytes, and when to choose each format.

APNG wins on browser support

Feature Support

Feature APNG FST-Image
Transparency (Alpha) Yes ✕ No
Animation Support Yes ✕ No
Progressive Loading Yes ✕ No
HDR Support ✕ No ✕ No
EXIF Metadata Yes ✕ No
ICC Color Profile Yes ✕ No
Animated Portable Network Graphics
image/vnd.mozilla.apng
Extension
.apng.png
Container PNG Chunk Stream
Compression Deflate (Lossless)
Algorithm
Deflate (zlib)
Color Depth 8-bit (Indexed), 24-bit (TrueColor), 32-bit (RGBA)
Developed by Mozilla Corporation (Stuart Parmenter & Vladimir Vukićević)
Released 2004
Magic Bytes
89 50 4E 47 0D 0A 1A 0A
Full APNG reference →
FAST Search & Transfer Image
image/vnd.fst
Extension
.fst
Container Proprietary FAST Container
Compression Proprietary
Algorithm
Unknown (Proprietary FAST encoding)
Color Depth Unknown
Developed by FAST Search & Transfer ASA (Arild Fuldseth)
Released 2000
Magic Bytes
Unknown (Proprietary)
Full FST-Image reference →

Browser Support Comparison

Browser APNG FST-Image
Chrome Chrome
✓ 59
 ✕
Firefox Firefox
✓ 3
 ✕
Safari Safari
✓ 8
 ✕
Edge Edge
✓ 79
 ✕
IE IE (Legacy)
✕ ✕
APNG

APNG Strengths

  • Supports 8-bit alpha transparency, completely solving the ugly 'white halo' problem inherent to GIFs
  • Gracefully degrades; viewers that do not support APNG will render a perfectly valid, static PNG of the first frame
  • Provides lossless compression that retains absolute pixel-perfect quality for UI elements and line art
Limitations
  • Because it relies on lossless Deflate compression, file sizes for complex, video-like animations can be massive compared to lossy formats like WebP or AVIF
  • Was initially rejected by the official PNG group, delaying its adoption for nearly a decade
  • Lacks native hardware decoding acceleration, unlike video-based animated formats (like MP4 or WebM)
FST-Image

FST-Image Strengths

  • Historically served as an optimized, compressed format for FAST's early multimedia and live streaming engines over constrained late-1990s bandwidth
Limitations
  • Completely obsolete and non-functional in modern software ecosystems
  • Undocumented, closed-source binary structure with zero support in modern image processing libraries
  • Shares its file extension with several other distinct file types (such as FL Studio state files or FAST Search dictionaries), leading to easy misidentification

When to choose which format

APNG
Use APNG when…
  • High-Quality Web Animations
  • Stickers (Apple iMessage, LINE, Discord)
  • UI Loaders with Alpha Transparency
  • GIF Replacement
FST-Image
Use FST-Image when…
  • Historical FAST Enterprise Search Indexing
  • Legacy Proprietary Multimedia Streaming (late 1990s)
  • Internal Media Transmission

More comparisons

APNG vs ACES → FST-Image vs ACES → APNG vs AVCI → FST-Image vs AVCI → APNG vs AVCS → FST-Image vs AVCS → APNG vs AVIF → FST-Image vs AVIF → All comparisons →
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