Free webp to jpg
EN
Image MIME Reference
ICO

Windows Icon (Legacy MIME)

image/x-icon
VS

RealNetworks RealFlash

image/vnd.rn-realflash
RealFlash

A complete technical comparison of Windows Icon (Legacy MIME) and RealNetworks RealFlash — covering compression, feature support, browser compatibility, magic bytes, and when to choose each format.

ICO wins on browser support

Feature Support

Feature ICO RealFlash
Transparency (Alpha) Yes Yes
Animation Support ✕ No Yes
Progressive Loading ✕ No Yes
HDR Support ✕ No ✕ No
EXIF Metadata ✕ No ✕ No
ICC Color Profile ✕ No ✕ No
Windows Icon (Legacy MIME)
image/x-icon
Extension
.ico
Container ICO Directory Structure
Compression Uncompressed (DIB/BMP) / Deflate (Embedded PNG)
Algorithm
NoneDeflate (via PNG)
Color Depth 1-bit, 4-bit, 8-bit, 24-bit (True Color), 32-bit (RGBA)
Developed by Microsoft Corporation
Released 1985
Magic Bytes
00 00 01 00
Full ICO reference →
RealNetworks RealFlash
image/vnd.rn-realflash
Extension
Container RealMedia / SWF
Compression Vector (Flash) / RealAudio Compression
Algorithm
Macromedia Vector CompressionDeflate (Zlib)
Color Depth 8-bit, 24-bit, 32-bit
Developed by RealNetworks & Macromedia
Released 1997
Magic Bytes
46 57 53 (FWS - Standard Flash) or 2E 52 4D 46 (.RMF - RealMedia Container)
Full RealFlash reference →

Browser Support Comparison

Browser ICO RealFlash
Chrome Chrome
✓ 1
 ✕
Firefox Firefox
✓ 1
 ✕
Safari Safari
✓ 1
 ✕
Edge Edge
✓ 12
 ✕
IE IE (Legacy)
✓
 ✕
ICO

ICO Strengths

  • Universally supported by every web browser in existence for website favicons
  • Packs multiple resolutions into a single file, eliminating the need to serve different files for the taskbar vs. the desktop
  • Modern support for embedded PNGs (since Windows Vista) allows for excellent 32-bit transparency (alpha channels) and drastically reduced file sizes
Limitations
  • Internal file structure is convoluted due to decades of legacy cruft, such as the requirement for BMP data to lack a standard file header but double the height property for an archaic XOR/AND mask
  • Larger file size compared to a single optimized PNG or SVG, as it literally stores the same image multiple times at different scales
  • The MIME type landscape is highly fragmented (x-icon vs. vnd.microsoft.icon), causing occasional caching or strict-MIME validation errors on restrictive servers
RealFlash

RealFlash Strengths

  • Allowed complex, interactive vector animations to stream smoothly over 28.8k dial-up modems
  • Perfectly synchronized streaming audio with timeline-based animations, which was revolutionary in 1997
Limitations
  • Heavily reliant on proprietary browser plugins (RealPlayer), which were notoriously bloated
  • Completely obsolete and unsupported on the modern web
  • Tightly coupled server-client architecture required expensive RealServer licenses to host

When to choose which format

ICO
Use ICO when…
  • Website Favicons (favicon.ico)
  • Windows Application Executable Icons (.exe)
  • Desktop Shortcut Icons
RealFlash
Use RealFlash when…
  • Historical Dial-up Web Animation
  • Late-1990s Interactive Music Videos
  • Streaming Vector Graphics

More comparisons

ICO vs ACES → RealFlash vs ACES → ICO vs APNG → RealFlash vs APNG → ICO vs AVCI → RealFlash vs AVCI → ICO vs AVCS → RealFlash vs AVCS → ICO vs AVIF → RealFlash vs AVIF → All comparisons →
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