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Image MIME Reference
AVCS

AVC Image Sequence (HEIF Container)

image/avcs
VS

Free Lossless Image Format

image/flif
FLIF

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

Equal browser support

Feature Support

Feature AVCS FLIF
Transparency (Alpha) Yes Yes
Animation Support Yes Yes
Progressive Loading ✕ No Yes
HDR Support Yes Yes
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 →
Free Lossless Image Format
image/flif
Extension
.flif
Container FLIF Bitstream
Compression Lossless (MANIAC Entropy Coding)
Algorithm
MANIAC (Meta-Adaptive Near-zero Integer Arithmetic Coding)
Color Depth 1-bit to 16-bit (Per Channel), Grayscale, RGB, RGBA, CMYK
Developed by Jon Sneyers and Pieter Wuille (Cloudinary)
Released 2015
Magic Bytes
46 4C 49 46
Full FLIF reference →

Browser Support Comparison

Browser AVCS FLIF
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  • Largely superseded in efficiency by newer sequence formats like HEICS (HEVC) or Animated AVIF (AV1)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
FLIF

FLIF Strengths

  • Achieves some of the highest lossless compression ratios ever developed for raster images
  • Incredible progressive decoding allows an image to be highly recognizable even after only 5% of the file has been downloaded
  • Supports animations and complex alpha channels losslessly
Limitations
  • Officially abandoned in favor of JPEG XL
  • Zero native support in web browsers or standard operating system previewers
  • Encoding speed can be significantly slower than standard PNG or WebP compression

When to choose which format

AVCS
Use AVCS when…
  • Burst Photography
  • Short Animations
  • Camera Capture
  • Archival Storage
FLIF
Use FLIF when…
  • Archival of Uncompressed Image Assets
  • Bandwidth-Constrained Progressive Image Loading (Historical)
  • Medical and Scientific Imaging Storage

More comparisons

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