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Image MIME Reference
AVCS

AVC Image Sequence (HEIF Container)

image/avcs
VS

FlashPix

image/vnd.fpx
FPX

A complete technical comparison of AVC Image Sequence (HEIF Container) and FlashPix — covering compression, feature support, browser compatibility, magic bytes, and when to choose each format.

Equal browser support

Feature Support

Feature AVCS FPX
Transparency (Alpha) Yes Yes
Animation Support Yes ✕ No
Progressive Loading ✕ No ✕ No
HDR Support Yes ✕ No
EXIF Metadata Yes Yes
ICC Color Profile Yes Yes
AVC Image Sequence (HEIF Container)
image/avcs
Extension
.avcs.heifs
Container HEIF / ISOBMFF (ISO/IEC 14496-12)
Compression Lossy / Lossless
Algorithm
AVC (Advanced Video Coding / H.264)
Color Depth 8-bit, 10-bit, 12-bit
Developed by Moving Picture Experts Group (MPEG) / ISO/IEC JTC 1
Released 2015
Magic Bytes
XX XX XX XX 66 74 79 70 61 76 63 73
Full AVCS reference →
FlashPix
image/vnd.fpx
Extension
.fpx
Container Microsoft OLE Structured Storage (COM)
Compression JPEG (Lossy) / Uncompressed / Single-color (Solid)
Algorithm
JPEGNone
Color Depth 8-bit (Grayscale/Indexed), 24-bit (RGB), 32-bit (CMYK/RGBA)
Developed by Eastman Kodak, Microsoft, Hewlett-Packard, Live Picture
Released 1996
Magic Bytes
D0 CF 11 E0 A1 B1 1A E1
Full FPX reference →

Browser Support Comparison

Browser AVCS FPX
Chrome Chrome
✕ ✕
Firefox Firefox
✕ ✕
Safari Safari
✕ ✕
Edge Edge
✕ ✕
IE IE (Legacy)
✕ ✕
AVCS

AVCS Strengths

  • Efficiently stores bursts of images or animations utilizing inter-frame compression
  • Leverages the highly compatible and widely hardware-accelerated AVC (H.264) codec
  • Robust HEIF container supports extensive metadata, alpha channels, and depth maps
Limitations
  • Zero native support in web browsers
  • Largely superseded in efficiency by newer sequence formats like HEICS (HEVC) or Animated AVIF (AV1)
  • Complicated container structure requires specialized parsing libraries
FPX

FPX Strengths

  • Allowed early, low-RAM computers to view and edit massive, high-resolution digital photos instantly by only loading the needed tiles and resolutions
  • Pioneered the multi-resolution pyramid and tiling concepts heavily used today in modern deep-zoom and web mapping applications (like Google Maps)
Limitations
  • Completely obsolete and unsupported by modern web browsers or operating systems
  • Uses the complex, proprietary Microsoft OLE container format, making it incredibly difficult to parse or extract data from without dedicated legacy libraries
  • Prone to being misidentified by MIME sniffers as an old Microsoft Office document

When to choose which format

AVCS
Use AVCS when…
  • Burst Photography
  • Short Animations
  • Camera Capture
  • Archival Storage
FPX
Use FPX when…
  • Legacy Digital Photography
  • Kodak Picture CDs (Historical)
  • Early High-Resolution Image Viewers

More comparisons

AVCS vs ACES → FPX vs ACES → AVCS vs APNG → FPX vs APNG → AVCS vs AVCI → FPX vs AVCI → AVCS vs AVIF → FPX vs AVIF → All comparisons →
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