Feature Overview

The work in dash.js is closely aligned with the work on the DASH Interoperability Points and the DASH Live Simulator 2 in DASH-IF.

DASH-IF IOP Alignment

IOP Documentation	dash.js	LiveSim 2
Live2VoD	Supported	Supported
L3D	Supported, see also here	Supported via chunked delivery (chunkdur) and availabilityTimeOffset
Content Steering	Supported but needs some updates to be compliant with version 1.0.0. See also here	Supported: multiple service locations, trigger and rotate modes, queryBeforeStart
MPD Patch	Supported, see also here	Supported via configurable Patch TTL
CMCD	Version 1 fully supported, version 2 including event and response mode reporting, see also here	Not supported
CMSD	Implementation completed for two attributes etp and mb, see also here	Not supported
Variable Substitution / DASH Annex I	Basic support, no support for templating mechanism. See also here	Supported: query parameters are propagated to segment requests
Server Guided Ad Insertion	Not supported	Supported: DASH 6th edition Alternative-MPD Replace events, break schedules, skippability signaling
DRM / CPIX	Supported, see also here	Supports on-the-fly encryption (ECCP cbcs/cenc) and EZDRM (Widevine, PlayReady, FairPlay)
LC-EVC	Basic support, see also here	Not supported

dash.js Features

Core Playback

Feature	Notes
VoD and live playback	MPEG-DASH playback via the Media Source Extensions (MSE)
Multi-period streams	Seamless transitions between periods, see Multiperiod Streams
Track selection	Initial and runtime selection by language, role, codec and custom filters, see Track Selection
Gap handling	Automatic detection and handling of buffer gaps and missing segments
Microsoft Smooth Streaming	Playback of Smooth Streaming assets via a separate bundle, see MSS
Multiple players per page	Each MediaPlayer instance runs in its own scope

Live & Low Latency

Feature	Notes
Low latency streaming	CMAF chunked transfer playback with configurable target latency, see Low Latency
Catchup mechanisms	Playback rate adjustment to reach and hold the live edge
Clock synchronization	UTCTiming support to align client and server clocks, see Clock Synchronization
MPD patching	Delta manifest updates instead of full MPD reloads, see MPD Patching
Live streaming settings	Time-shift buffer, live delay and update handling, see Live Streaming

Adaptive Bitrate (ABR)

Feature	Notes
Default ABR rules	ThroughputRule, BolaRule, InsufficientBufferRule, SwitchHistoryRule, DroppedFramesRule, AbandonRequestRule, see ABR
Low latency ABR rules	L2A and LoL+ for chunked low latency streams
Custom rules	Own ABR rules are pluggable via the rules API
Manual quality selection	Explicit representation selection per media type, see Manual Quality Selection
Buffer management	Configurable buffer targets and pruning, see Buffer Management

DRM & Content Protection

Feature	Notes
Key systems	Widevine, PlayReady, FairPlay and ClearKey via the Encrypted Media Extensions (EME), see DRM
Encryption schemes	CENC (cenc) and CBCS (cbcs)
License configuration	Custom license server URLs, request/response filters, priority per key system
Robustness levels	Configurable audio/video robustness

Subtitles & Captions

Feature	Notes
Segmented TTML / IMSC1	Fragmented and non-fragmented TTML, see Subtitles & Captions
WebVTT	Including custom rendering, see Custom WebVTT Rendering
CEA-608/708	In-band closed captions embedded in the video stream
External subtitles	Attaching external subtitle files at runtime
DVB font downloading	Downloadable fonts signaled in the MPD, see DVB Font Downloading

Data, Events & Reporting

Feature	Notes
CMCD	Common Media Client Data version 1 and 2, see CMCD
CMSD	Common Media Server Data (etp, mb), see CMSD
MPD and inband events	EventStream and emsg handling with application callbacks, see Event Handling
Metrics and player events	Extensive playback metrics and event API, see Player Events

Advanced

Feature	Notes
Content steering	Multi-CDN switching driven by a steering server, see Content Steering
Network interceptors	Custom request/response interceptors in the loading stack, see Network Interceptor
URL parameter insertion	DASH Annex I flexible insertion of URL parameters, see Flexible Insertion of URL Parameters
Preloading	Buffering content before a video element is attached, see Preloading
Thumbnails	Thumbnail tracks based on image adaptation sets, see Thumbnails
LC-EVC	Basic support for LC-EVC enhanced streams, see LCEVC
Offline playback	Downloading streams for offline playback

Testing with LiveSim2

LiveSim2 is the DASH-IF live source simulator. It turns VoD assets into wall-clock synchronized, infinite live streams and is publicly hosted at livesim2.dashif.org. The URL generator allows interactive configuration of test streams, which makes it a good companion for testing dash.js:

• Segment addressing: SegmentTemplate with $Number$ or $Time$, and SegmentTimeline variants
• Low latency: chunked delivery with configurable chunk duration and availabilityTimeOffset
• Multi-period: configurable number of periods per hour, period continuity signaling
• Timing: all common UTCTiming methods (direct, HTTP head, xsdate, iso, NTP, SNTP)
• Ad insertion: SCTE-35 emsg events and Server-Guided Ad Insertion with Alternative-MPD Replace events
• Subtitles: generated stpp and wvtt subtitles for any number of languages, CEA-608 in-band captions
• Encryption: on-the-fly ECCP (cbcs/cenc) encryption and EZDRM integration (Widevine, PlayReady, FairPlay)
• Content steering: multiple service locations with trigger or rotate mode
• MPD Patch: delta manifest updates with configurable Patch TTL
• Negative testing: cyclic segment error codes (404/403) and traffic patterns (down, slow, hang) for robustness testing
• CMAF ingest: acts as a CMAF ingest source (version 1.1) pushing segments to a configurable destination