cs 414 – multimedia systems design lecture 27 – dash (dynamic adaptive streaming over http)
DESCRIPTION
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. Media encaps (H.264, MPEG-4). Synchronization Service. DASH. - PowerPoint PPT PresentationTRANSCRIPT
CS 414 - Spring 2012
CS 414 – Multimedia Systems Design Lecture 27 – DASH (Dynamic Adaptive Streaming over HTTP)
Klara NahrstedtSpring 2012
Administrative MP2 posted MP2 Deadline – April 7, Saturday, 5pm.
CS 414 - Spring 2012
Internet Multimedia Protocol Stack
CS 414 - Spring 2012
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
ATIO
N
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
…
CS 414 - Spring 2012
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
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Growth of Mobile Internet/Video
Thomas Stockhammer, Qualcomm, “DASH – Design Principles and Standards , MMSys 2011
Adaptive Streaming
One approach to tackle problems/challenges
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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 Streaming1. 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 allowsSecond Approach of Adaptive Streaming1.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 Streaming1.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
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Client-centric approach
Client has best view of network conditions No session state in network
RedundancyScalability
Faster innovation and experimentation But, relies on client for operational metrics
Only client knows what really happens
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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
CS 414 - Spring 2012
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 2012Source: MMSys’11
Media Presentation Data ModelMDP - 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
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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)
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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
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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
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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, …
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Composition of Media Presentation (CMP)Consider layer on top of MDP which specifies initial user and device optionsReasons:
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
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CMP Protocol Sequence
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(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)
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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
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(1) Initiate session transfer(2) Digital Item Adaptation (DIA)Starts and preserves current state of Digital Item (segment)(3) Transfer Context digital itemTo 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 2012Source: Watson, MMSys’11
Adaptive streaming in practice
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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
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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 - Spring 2012