cs 414 – multimedia systems design lecture 27 – dash

CS 414 - Spring 2012

CS 414 – Multimedia Systems Design Lecture 27 – DASH (Dynamic Adaptive Streaming over HTTP)

Klara Nahrstedt Spring 2012

Administrative MP2 posted MP2 Deadline – April 7, Saturday, 5pm.


Internet Multimedia Protocol Stack


AAL3/4

IP Version 4, IP Version 6

UDP

Media encaps (H.264, MPEG-4)

RTP

ATM/Fiber Optics Ethernet/WiFi

TCP

SIP RTSP RSVP RTCP

AAL5

KE

RN

EL

AP

PLIC

ATION

Layer 4 (Transport)

Layer 3 (Network)

Layer 2 (Link/MAC)

Layer 5 (Session)

MPLS

DCCP

DASH

HTTP

Synchronization Service

Problems with Internet Video

Video not accessible Video Behind firewall Plugins not available Bandwidth not

sufficient Wrong and non-trust

device Wrong format

Low Quality of Experience Long start-up latency Frequent rebuffering Low playback quality No lip-sync

…


Mobile Video Streaming Challenges Mobile Internet use is expanding

dramatically Video traffic is growing exponentially Challenges: Mobile users expect high quality video

experience Network operators need to offer quality

experience affordably


Growth of Mobile Internet/Video

Thomas Stockhammer, Qualcomm, “DASH – Design Principles and Standards , MMSys 2011

Adaptive Streaming

One approach to tackle problems/challenges


Adaptive Streaming Concept Adaptive Streaming technologies enable

Optimal streaming video viewing experience for diverse range of devices over broad set of connection speeds

Adaptive streaming technologies share Production of multiple files from the same source file to

distribute to viewers watching on different powered devices via different connection speeds

Distribution of files adaptively, changing stream that is delivered to adapt to changes in effective throughput and available CPU cycles on playback stations

Transparent operation to the user so that the viewer clicks one button and all streams switch/adapt behind the scenes.

Adaptive Streaming

Source: http://www.dicomdistribution.com/Adaptive%20Streaming.html

One Approach of Adaptive Streaming 1. Server sends first the high important video information (e.g., I frames) And after the high importance video information is sent, lower importance video information follows (e.g., P and B frames) if bandwidth and time allows Second Approach of Adaptive Streaming 1. Server sends with high quality part of the frame and only progressively ,if bandwidth and time allow, it sends the rest of the frame information Third Approach of Adaptive Streaming 1. At server video is encoded in multiple bitrates and depending on the device Bandwidth it adjusts at what rate Other approaches exist

Standardization History

Thomas Stockhammer, Qualcomm, “DASH – Design Principles and Standards , Presentation at MMSys 2011

Adaptive HTTP Streaming System (Protocol)

Server Can be standard web

server Media segment can be

prepared in-line or off-line

Client Sends series of HTTP GET

segment requests and receives segments

Performs rate adaptation before sending a new GET segment request


Client-centric approach

Client has best view of network conditions No session state in network Redundancy Scalability

Faster innovation and experimentation But, relies on client for operational metrics Only client knows what really happens


Terms and Definitions of Adaptive HTTP Streaming Need Media Presentation Description (MDP)

which provides metadata For requesting (GET request) media segments For rate adaptation purpose

Segment which may include media data or metadata to decode

Need DASH


DASH – Dynamic Adaptive Streaming over HTTP Dash is NOT

System, protocol, presentation, codec, interactivity

What is DASH Enabler which provides formats to enable efficient and high-

quality delivery of streaming services over the Internet Component of end-to-end service Enabler to reuse existing technologies (containers, DRM

(Digital Rights Management), codecs) Enabler for deployment on top of HTTP-CDNs Enabler for very high user experience (low start-up, no re-

buffering) Provides simple inter-operability points (profiles)

DASH Client

Thomas Stockhammer, Qualcomm, “DASH – Design Principles and Standards , Presentation at MMSys 2011

Information Classification DASH uses MPD (Media Presentation Descriptor) and

Index Information as metadata for DASH Access Client Initialization and Media Segments for Media Engine

Reuse of existing container format

CS 414 - Spring 2012 Source: MMSys’11

Media Presentation Data Model MDP - description of accessible segments and corresponding timing

Source: Stockhammer, Qualcomm, “DASH – Design Principles and Standards , Presentation at MMSys 2011

MDP Information Includes redundant information of media

streams to initially select or reject groups or representations

Includes access and timing information Content addressing via HTTP-URLs Byte range for each accessible segment Segment availability start and end time in wall-clock time Approximate media start time and duration Instructions on starting playout (for live service)

Includes switching relations across representations


Media Segments (1)

Contain information to map segment into media presentation timeline for switching and synchronous presentation with other representations

Can be short (~ 1-10seconds) Can be long (~10sec – 2 hours)


Media Segments (2) Media segment duration

advantages disadvantages

Short duration Commonality with live high switching granularity on segment level

- Large number of files - Large number of

URLs - Fixed request size - Switching granularity

on segment level Long duration - Small number of files

- Small number of URLs - High switching

granularity - Flexible request sizes - Improved cache

performance

- Need for segment index

- Difference from live


Segment Indexing

Provides information in ISO box structure on Accessible units of data (e.g., frames) in media segment Byte range in segments (easy access through HTTP

GET) Accurate presentation duration (seamless switching) Presence of representation access positions

Provides compact bitrate-over-time to client Can be used for intelligent request schedule

Generic data structure Hierarchical structuring for efficient access


Media Segment with Segment Index

Source: Stockhammer, Qualcomm, “DASH – Design Principles and Standards , Presentation at MMSys 2011

DASH Capabilities Enables live, on-demand and time-shift services Allows independency of request sizes and segment sizes Allows segment formats that are

ISO base media formats – ISO BMFF or MPEG-2 TS ISO BMFF - .. File Format (extensions) MPEG-2 TS - .. Transport Stream (extensions)

Guidelines for integrating any other format Codec independent

Supports server/client component synchronization (e.g., separate and multiplexed AV)

Enables targeted ad insertion Provides definition of quality metrics Enables content descriptors for protection, accessibility, rating, …


Composition of Media Presentation (CMP) Consider layer on top of MDP which specifies initial user and device options Reasons:

Size of MPD expands very quickly (different camera views/angles, subtitles, audio languages, …)

Device pre-configuration (codec, resolution…) User pre-configuration due to her preferences

(camera angle, subtitle, …) Flexibility and compatibility with existing repository

formats CS 414 - Spring 2012

CMP Protocol Sequence


(1) At Client Request CMP from Server (1) Once CMP received, check and Configure CMP at client if needed (3) Request for MDP that fulfills Requirements (4) Start standard DASH complaint steps

Source: Muller et al, MMSys’11

DASH featuring Session Mobility (Problem Description)


Problem: User runs DASH streaming session on laptop and decides to switch to Another mobile device

Source: Muller et al, MMSys’11

Session Mobility Protocol


(1) Initiate session transfer (2) Digital Item Adaptation (DIA) Starts and preserves current state of Digital Item (segment) (3) Transfer Context digital item To selected device (4) Download CMP (5) Reconfigure device (6) Continue with DASH-compatible protocol

Source: Muller et al. MMSys 2011

Adaptive streaming in practice

CS 414 - Spring 2012 Source: Watson, MMSys’11

Adaptive streaming in practice


MPEG DASH Summary Is rich and simple at the same time Supports both un-chunked and chunked Supports both separate and combined AV Index formats for efficient byte range operation ISO base media file format w/common

encryption Many useful stream and track annotations Currently – best candidate for open standard

for adaptive streaming


Conclusion Metadata used by DASH and session

mobility approach use MPEG-21 international standard Facilitates MPEG-21 Digital Item Leverages existing media repositories such

as UPnP One possible implementation of DASH http://www-itec.uni-klu.ac.at/dash


cs 414 – multimedia systems design lecture 27 – dash

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