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Image MIME Reference
HEIC-Sequence

HEVC Image Sequence (HEIF Container)

image/heic-sequence
VS

Valve Texture Format

image/vnd.valve.source.texture
VTF

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

HEIC-Sequence wins on browser support

Feature Support

Feature HEIC-Sequence VTF
Transparency (Alpha) Yes Yes
Animation Support Yes Yes
Progressive Loading ✕ No ✕ No
HDR Support Yes Yes
EXIF Metadata Yes ✕ No
ICC Color Profile Yes ✕ No
HEVC Image Sequence (HEIF Container)
image/heic-sequence
Extension
.heics.heic
Container HEIF / ISOBMFF (ISO/IEC 14496-12)
Compression Lossy / Lossless
Algorithm
HEVC (H.265)
Color Depth 8-bit, 10-bit, 12-bit, 16-bit
Developed by Moving Picture Experts Group (MPEG) / Apple
Released 2017
Magic Bytes
XX XX XX XX 66 74 79 70 68 65 76 63
Full HEIC-Sequence reference →
Valve Texture Format
image/vnd.valve.source.texture
Extension
.vtf
Container Valve Texture Format Header
Compression DXTC (DXT1, DXT3, DXT5) / Uncompressed (BGRA8888, RGB888, etc.)
Algorithm
DXT1-DXT5None
Color Depth 8-bit, 24-bit (RGB), 32-bit (RGBA), 16-bit Floating Point (HDR)
Developed by Valve Corporation
Released 2004
Magic Bytes
56 54 46 00
Full VTF reference →

Browser Support Comparison

Browser HEIC-Sequence VTF
Chrome Chrome
✕ ✕
Firefox Firefox
✕ ✕
Safari Safari
✓ 11+
 ✕
Edge Edge
✕ ✕
IE IE (Legacy)
✕ ✕
HEIC-Sequence

HEIC-Sequence Strengths

  • Incredibly efficient storage for bursts and short animations compared to GIF or motion JPEG
  • Supports 16-bit color, HDR, and alpha channel transparency across all frames
  • Shares frame data blocks, meaning the base image and animation data are heavily optimized for space
Limitations
  • Zero support in web browsers outside the Apple ecosystem (Chrome, Firefox, Edge do not support it)
  • Heavily encumbered by HEVC patent pools, hindering open-source adoption
  • Complex container structure makes parsing and decoding difficult without specialized libraries
VTF

VTF Strengths

  • Extremely fast loading within the Source Engine because the block-compressed data goes directly into the GPU's VRAM without CPU decompression overhead
  • Bundles mipmaps, volumetric slices, cubemap faces, and animation frames entirely within a single file
  • Openly documented by the Valve Developer Community, leading to a massive ecosystem of third-party modding tools
Limitations
  • Strictly tied to the Source Engine ecosystem; entirely useless in standard web or print contexts
  • No native support in standard image editors without hunting down and installing specialized plugins
  • Block compression algorithms (DXT) are lossy and can cause visible artifacting, especially on normal maps or smooth gradients

When to choose which format

HEIC-Sequence
Use HEIC-Sequence when…
  • Apple Live Photos
  • Burst Photography
  • High-Quality Animations
  • Cinemagraphs
VTF
Use VTF when…
  • Source Engine Game Textures
  • Custom Maps and Modding (Garry's Mod, CS:GO)
  • Animated In-Game Decals and Sprays
  • Environment Cubemaps (Skyboxes)

More comparisons

HEIC-Sequence vs ACES → VTF vs ACES → HEIC-Sequence vs APNG → VTF vs APNG → HEIC-Sequence vs AVCI → VTF vs AVCI → HEIC-Sequence vs AVCS → VTF vs AVCS → HEIC-Sequence vs AVIF → VTF vs AVIF → All comparisons →
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