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.