Image MIME Reference
HEIC-Sequence
HEVC Image Sequence (HEIF Container)
image/heic-sequence
VS
Portable Network Graphics (Legacy MIME)
image/x-png
PNG
A complete technical comparison of HEVC Image Sequence (HEIF Container) and Portable Network Graphics (Legacy MIME) — covering compression, feature support, browser compatibility, magic bytes, and when to choose each format.
PNG wins on browser support
Feature Support
| Feature | HEIC-Sequence | PNG |
|---|---|---|
| Transparency (Alpha) | Yes | Yes |
| Animation Support | Yes | ✕ No |
| Progressive Loading | ✕ No | Yes |
| HDR Support | Yes | Yes |
| EXIF Metadata | Yes | Yes |
| ICC Color Profile | Yes | Yes |
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
Portable Network Graphics (Legacy MIME)
image/x-png
Extension
.png
Container
PNG Chunk Structure (IHDR, IDAT, IEND)
Compression
Deflate (Lossless)
Algorithm
Deflate (LZ77)
Color Depth
1-bit to 16-bit (Grayscale), 8-bit (Indexed Palette), 24-bit (True Color), 32-bit (True Color with Alpha), 48-bit (High Color), 64-bit (High Color with Alpha)
Developed by
PNG Development Group
Released
1996
Magic Bytes
89 50 4E 47 0D 0A 1A 0A
Browser Support Comparison
| Browser | HEIC-Sequence | PNG |
|---|---|---|
Chrome
|
✕ |
✓ 1
|
Firefox
|
✕ |
✓ 1
|
Safari
|
✓ 11+
|
✓ 1
|
Edge
|
✕ |
✓ 12
|
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
PNG
PNG Strengths
- The underlying format provides flawless, lossless compression and perfect 8-bit alpha channel transparency
- Universally supported by every modern operating system, image editor, and web browser
Limitations
- The 'image/x-png' string is an obsolete vendor quirk that forces backend developers to write redundant normalization logic in file upload scripts
- If left unnormalized, strict MIME validators or content security policies on modern systems may incorrectly reject valid PNG files
When to choose which format
HEIC-Sequence
Use HEIC-Sequence when…
- Apple Live Photos
- Burst Photography
- High-Quality Animations
- Cinemagraphs
PNG
Use PNG when…
- Legacy Internet Explorer File Uploads
- Older ASP/PHP Web Applications
- Lossless Web Graphics