HLS vs DASH: Adaptive Streaming Explained

Adaptive bitrate streaming (ABR) solves a fundamental problem: how to deliver video smoothly across varying network conditions and devices.

The process:

1. Encoding: Source video is transcoded into multiple quality levels (renditions)
2. Segmentation: Each rendition is divided into small chunks (2-10 seconds each)
3. Manifest: A playlist file lists all available renditions and segment URLs
4. Playback: The player monitors bandwidth and buffer, switching between qualities automatically

When bandwidth drops, the player switches to a lower quality rendition to prevent buffering. When bandwidth improves, it switches up for better quality. This happens seamlessly, often mid-stream.

Developed by Apple, HLS is required for video playback on iOS and Safari. It's the most widely supported adaptive streaming format.

How HLS works:

• Master playlist (.m3u8) lists all available renditions
• Each rendition has its own media playlist listing segments
• Segments traditionally use .ts (MPEG-TS) format, but fMP4 is now preferred
• Default segment duration is 6 seconds, though 2-4 seconds is common for lower latency

HLS advantages:

• Required for iOS/Safari—no alternative
• Mature tooling and widespread support
• Built-in DRM support via FairPlay
• Simple playlist format (plain text)

HLS limitations:

• Originally proprietary (now RFC 8216)
• Higher latency with default settings
• .ts segments are less efficient than fMP4

DASH is an ISO standard (ISO/IEC 23009-1) not controlled by any single vendor. It's the default for YouTube, Netflix (on non-Apple devices), and most Android applications.

How DASH works:

• MPD (Media Presentation Description) manifest in XML format
• Segments use .m4s (fragmented MP4) format
• More flexible than HLS with advanced features
• Supports multiple DRM systems (Widevine, PlayReady)

DASH advantages:

• Open international standard
• More efficient fMP4 segments
• Advanced features (multiple periods, trick play)
• Better low-latency support

DASH limitations:

• Not supported on iOS/Safari natively
• More complex manifest format
• Less widespread than HLS overall

CMAF (Common Media Application Format) allows using the same fragmented MP4 segments for both HLS and DASH. Only the manifests differ.

Benefits of CMAF:

• 50% storage reduction: One set of segments serves both protocols
• Simplified encoding: Encode once, deliver everywhere
• Better caching: CDN stores one copy for all viewers
• Lower latency: Chunked transfer encoding support

CMAF implementation:

• Encode to fMP4 segments with CMAF-compatible settings
• Generate both .m3u8 (HLS) and .mpd (DASH) manifests
• Same segments referenced by both manifests
• Major CDNs and players support CMAF

We typically recommend CMAF-based delivery for new projects. The storage and operational savings are significant.

Use HLS when:

• You must support iOS and Safari (you probably do)
• Simplicity is more important than advanced features
• Your CDN or encoding service prefers HLS

Use DASH when:

• You don't need iOS/Safari support
• You need advanced DRM (multi-key, offline)
• You're building for Android-only or web-only

Use both with CMAF when:

• You need maximum device coverage (recommended)
• You want to optimize storage and delivery costs
• You can invest in slightly more complex pipeline

For most projects, we recommend CMAF with both HLS and DASH manifests. This provides universal compatibility with optimal efficiency.