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Image MIME Reference
AVIF

AV1 Image File Format

image/avif
VS

RealNetworks RealFlash

image/vnd.rn-realflash
RealFlash

A complete technical comparison of AV1 Image File Format and RealNetworks RealFlash — covering compression, feature support, browser compatibility, magic bytes, and when to choose each format.

AVIF wins on browser support

Feature Support

Feature AVIF RealFlash
Transparency (Alpha) Yes Yes
Animation Support Yes Yes
Progressive Loading ✕ No Yes
HDR Support Yes ✕ No
EXIF Metadata Yes ✕ No
ICC Color Profile Yes ✕ No
AV1 Image File Format
image/avif
Extension
.avif
Container HEIF / ISOBMFF
Compression AV1 Lossy / AV1 Lossless
Algorithm
AV1
Color Depth 8-bit, 10-bit, 12-bit
Developed by Alliance for Open Media (AOMedia)
Released 2019
Magic Bytes
XX XX XX XX 66 74 79 70 61 76 69 66
Full AVIF 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 AVIF RealFlash
Chrome Chrome
✓ 85+
 ✕
Firefox Firefox
✓ 93+
 ✕
Safari Safari
✓ 16+
 ✕
Edge Edge
✓ 121+
 ✕
IE IE (Legacy)
✕ ✕
AVIF

AVIF Strengths

  • Best-in-class compression — typically 20–50% smaller than WebP at equivalent quality
  • Native HDR and wide color gamut (BT.2020) support
  • Supports 8, 10, and 12-bit color depth
Limitations
  • Encoding is highly CPU-intensive — significantly slower than JPEG or WebP
  • Requires Edge 121+ (not supported in earlier Edge versions)
  • Limited support in native desktop image viewers
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

AVIF
Use AVIF when…
  • Next-Gen Websites
  • HDR Photography
  • High-Quality Web Images
RealFlash
Use RealFlash when…
  • Historical Dial-up Web Animation
  • Late-1990s Interactive Music Videos
  • Streaming Vector Graphics

More comparisons

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