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Image MIME Reference
HEIF-Sequence

High Efficiency Image File Format Sequence

image/heif-sequence
VS

Valve Texture Format

image/vnd.valve.source.texture
VTF

A complete technical comparison of High Efficiency Image File Format Sequence and Valve Texture Format — covering compression, feature support, browser compatibility, magic bytes, and when to choose each format.

Equal browser support

Feature Support

Feature HEIF-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
High Efficiency Image File Format Sequence
image/heif-sequence
Extension
.heifs.heif.hif
Container HEIF / ISOBMFF (ISO/IEC 14496-12)
Compression Lossy / Lossless
Algorithm
Codec Agnostic (HEVC, AVC, JPEG, AV1)
Color Depth 8-bit, 10-bit, 12-bit, 16-bit
Developed by Moving Picture Experts Group (MPEG)
Released 2015
Magic Bytes
XX XX XX XX 66 74 79 70 6D 73 66 31
Full HEIF-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 HEIF-Sequence VTF
Chrome Chrome
✕ ✕
Firefox Firefox
✕ ✕
Safari Safari
✕ ✕
Edge Edge
✕ ✕
IE IE (Legacy)
✕ ✕
HEIF-Sequence

HEIF-Sequence Strengths

  • Codec-agnostic container allows for extreme flexibility when storing multi-frame photographic data
  • Maintains the space-saving benefits of ISOBMFF shared frame data blocks
  • Excellent for archiving computational photography workloads like exposure brackets or focal stacks
Limitations
  • Codec ambiguity means a decoder might be able to parse the container but fail to decode the underlying pixels
  • Zero native web browser support
  • Complex container structure requires specialized parsing libraries to extract individual frames
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

HEIF-Sequence
Use HEIF-Sequence when…
  • Burst Photography
  • Focal Stacking
  • Exposure Bracketing
  • Time-Lapse Data
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

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