Presented at SCREENS 2013 in Toronto. Details at fitc.ca/screens This session will explore the leading edge in the world of video delivery, an open standard, supported by the industry’s biggest players, named MPEG-DASH and its companion project dash.js. While we are constantly building DASH players for platforms including Desktop, Browser, Flash, Connected TVs and Mobile Devices, dash.js offers the promise of high-quality streams in a JavaScript client. As the lead architect on the dash.js project, the speaker has intimate knowledge of the inner workings of this project, and he is actively collaborating with contributors from Microsoft, Google and others. The technology for dash.js is new, and it’s not yet supported on every device, but we are working with many of the key players to make it a reality and the list of supported devices grows daily. So join us while weexplore the DASH standard, discuss how dash players are built, dig through the dash.js codebase, and see dash playing on mobile devices.

1. Next Generation Streaming
Video
Jeff Tapper
Digital Primates
@jefftapper

2. Who am I?
• Senior Consultant at Digital Primates
– Building next generation client applications
• Built video applications for many of the most
watched live broadcasts
• Developing Internet applications for 17 years
• Author of 12 books on Internet technologies

3. Who are you?

4. Agenda
• Video and the Internet today
• Understanding HTTP Streaming
• What are the Streaming options without a
plugin?
• What is DASH
• What is DASH-264
• Making it work in a browser
• Questions

5. Online video Options
• Progressive Download
• Real Time Protocols (RTP, RTMP, RTSP, etc)
• HTTP Streaming (HDS, HLS, Smooth
Streaming, etc)

6. The challenge
• Most agree that HTTP Streaming is the most
efficient choice
• Different devices support different streaming
protocols
• No one standard is currently supported
ubiquitously
• Results in media being served in several
different formats to support the broadest
range of devices

7. What do browsers support?
• Unfortunately, Progressive Download is the only
ubiquitously supported option
• Different Browsers support different video
codec’s
– H.264
– webM
– VP8
– Etc.
• Safari (iOs and MacOS only) natively supports HLS
• MediaSource Extensions in Chrome and IE11

8. MediaSource Extensions (MSE)
• MSE allow for pieces (segments) of media to
be handed to the HTML5 video tag’s buffer
directly.
• This enables HTTP Streaming in HTML
• Not universally supported, yet.
• Currently (as of 9/24) an Editors Draft of the
HTML Working Group

9. What is MPEG-DASH
 DASH – Dynamic Adaptive Streaming via HTTP
 International open standard, developed and
published by ISO
 Addresses both simple and advanced use cases
 Enables highest-quality multiscreen distribution
and efficient dynamic adaptive switching
 Enables reuse of existing content, devices and
infrastructure
 Attempts to unify to a single standard for HTTP
Streaming

10. DASH and codecs
• The DASH specification is codec agnostic
• Any existing or future codec can work with
DASH
• DASH manifest describes which codec is used
• Allows ability for a single manifest to describe
several different versions in different codecs

11. DASH264
• H.264 is dominant format today
• Many vendors and service providers are
committed to supporting/enabling DASH264
• Provides support for today’s requirements
such as DRM
• H.264 is backed by rigorous testing and
conformance

12. DASH Industry Forum
• Addressing the dramatic growth of broadband
video by recommending a universal delivery
format that provides end users with the best
possible media experience by dynamically
adapting to changing network conditions.

13. DASH Industry Forum
• Objectives:
– promote and catalyze market adoption of MPEG-DASH
– publish interoperability and deployment guidelines
– facilitate interoperability tests
– collaborate with standard bodies and industry
consortia in aligning ongoing DASH standards
development and the use of common profiles across
industry organizations
• Over 65 members
• Visit http://dashif.org for more information
• Released the DASH/264 standard

14. Building a DASH player
• We have built DASH players for several
different platforms
– Flash
– Android
– HTML5/JavaScript (dash.js)
• DASH.js is available as an open source project
(bsd3) on github
• DASH.js is the reference player for the DASH
Industry Forum (dashif.org)

15. How to play a DASH Stream
• Download Manifest
• Parse Manifest
• Determine optimal bandwidth for client
• Initialize for bandwidth
• Download Segment
• Hand segment to MSE
• Check Bandwidth to determine if change is
necessary

16. Understanding DASH structure
• Three types of files
– Manifest (.mpd)
• XML file describing the segments
– Initialization file
• Contains headers needed to decode bytes in segments
– Segment Files
• Contains playable media
• Includes:
– 0…many video tracks
– 0…many audio tracks

17. DASH Manifest
• Manifest contains:
– Root node
– 1 or more periods
• Periods contain 1 adaptation set per video stream and
• Periods contain 1 adaptation set per audio stream
• Adaptation Sets contain:
– Content Composition nodes (for each video or audio track)
– 1 or more Representation node
» Each representation describes a single bitrate
» Representations contain data on finding the actual segments
» Different ways a representation can describe segments

18. Describing Representations
• SegmentBase
– Describes a stream with only a single Segment per bitrate
– Can be used for Byte Range Requests
• SegmentList
– A SegmentList will contain a specific list of each
SegmentURL (individual HTTP packet with media data)
– Can be used for Byte Range Requests
• SegmentTemplate
– Defines a known url for the fragment with wildcards
resolved at runtime to request a segments (see bbb.mpd)
– Alternatively, can specify a list of segments based on
duration

19. SegmentList
<Representation id="h264bl_hd" mimeType="video/mp4"
codecs="avc1.42c01f" width="1280" height="720" startWithSAP="1"
bandwidth="514864">
<SegmentList timescale="1000" duration="10000">
<Initialization sourceURL="mp4-main-multi-h264bl_hd-.mp4"/>
<SegmentURL media="mp4-main-multi-h264bl_hd-1.m4s"/>
<SegmentURL media="mp4-main-multi-h264bl_hd-2.m4s"/>
<SegmentURL media="mp4-main-multi-h264bl_hd-3.m4s"/>
<SegmentURL media="mp4-main-multi-h264bl_hd-4.m4s"/>
<SegmentURL media="mp4-main-multi-h264bl_hd-5.m4s"/>
<SegmentURL media="mp4-main-multi-h264bl_hd-6.m4s"/>
<SegmentURL media="mp4-main-multi-h264bl_hd-7.m4s"/>
<SegmentURL media="mp4-main-multi-h264bl_hd-8.m4s"/>

20. SegmentTemplate fixed segment
duration
<AdaptationSet>
<ContentComponent id="1" contentType="video"/>
<SegmentTemplate
initialization="BigBuckBunny_720p_1800kbps_44khz_track1_dash.mp4"/>
<Representation id="1"
mimeType="video/mp4“ codecs="avc1.64001f"
width="1280" height="720“
startWithSAP="1" bandwidth="1809954">
<SegmentTemplate timescale="1000" duration="13809"
media="bbb_seg_BigBuckBunny_720p_1800kbps_44khz_track1$Number$.m4s"
startNumber="1"/>
</Representation>
</AdaptationSet>

21. SegmentTemplate variable segment
duration
<AdaptationSet group="2" mimeType="video/mp4" par="16:9“ minBandwidth="475000“
maxBandwidth="6589000" minWidth="176" maxWidth="1680"
minHeight="99" maxHeight="944“ segmentAlignment="true“
startWithSAP="1">
<SegmentTemplate timescale="1000"
initialization="dash/ateam-video=$Bandwidth$.dash"
media="dash/ateam-video=$Bandwidth$-$Time$.dash">
<SegmentTimeline>
<S t="0" d="4171" />
<S d="2503" />
<S d="2961" />
<S d="2461" />
<S d="2127" r="2" />
…

22. dash.js player

23. Tools used by dash.js
Core Player
• Q – Asynchronous handling with promises
• Dijon – DI / IOC
• Jasmine – unit tests
Web Site
• JQuery – DOM manipulation
• Flat-ui – UI elements
• Flot – Charting
• Kendo - Components

24. Class Structure
• The player is divided into two main packages.
• streaming – Contains the classes responsible
for creating and populating the MediaSource
buffers. These classes are intended to be
abstract enough for use with any segmented
stream (such as DASH, HLS, HDS and MSS).
• dash – Contains the classes responsible for
making decisions specifically related to Dash.

25. streaming package

26. MediaPlayer.js
• Exposes the top level functions and properties
to the developer (play, autoPlay, isLive, abr
quality, and metrics).
• The manifest URL and the HTML Video object
as passed to the MediaPlayer.

27. Context.js
• The dependency mapping for the stream
package.
• The context is passed into the MediaPlayer
object allowing for different MediaPlayer
instances to use different mappings.

28. Stream.js
• Loads/refreshes the manifest.
• Create SourceBuffers from MediaSource.
• Create BufferManager classes to manage
SourceBuffers.
• Responds to events from HTML Video object.
• For a live stream, the live edge is calculated
and passed to the BufferController instances.

29. Debug.js
• Convenience class for logging methods.
• Default implementation is to just use
console.log().
• Extension point for tapping into logging
messages.

30. BufferController.js
• Responsible for loading fragments and
pushing the bytes into the SourceBuffer.
• Once play() has been called a timer is
started to check the status of the bytes in the
buffer.
• If the amount of time left to play is less than
Manifest.minBufferTime the next fragment
is loaded.
• Records metrics related to playback.

31. FragmentLoader.js
• Responsible for loading fragments.
• Loads requests sequentially.
ManifestLoader.js
• Responsible for loading manifest files.
• Returns the parsed manifest object.

32. AbrController.js
• Responsible for deciding if the current quality
should be changed.
• The stream metrics are passed to a set of
‘rules’.
• Methods:
getPlaybackQuality(type, data)
 type – The type of the data
(audio/video).
 data – The stream data.

33. DownloadRatioRule.js
• Validates that fragments are being
downloaded in a timely manner.
• Compares the time it takes to download a
fragment to how long it takes to play out a
fragment.
• If the download time is considered a
bottleneck the quality will be lowered.

34. InsufficientBufferRule.js
• Validates that the buffer doesn’t run dry
during playback.
• If the buffer is running dry continuously it
likely means that the player has a processing
bottleneck (video decode time is longer than
playback time).

35. LimitSwitchesRule.js
• Watches for competing rules to avoid constant
bitrate switches.
• If two or more rules are causing switches too
often this rule will limit the switches to give a
better overall playback experience.

36. dash package

37. DashContext.js
• Defines dependency mapping specific to the
dash package.
– Parser
– Index Handler
– Manifest Extensions

38. DashParser.js
• Converts the manifest to a JSON object.
• Converts duration and datetime strings into
number/date objects.
• Manages inheritance fields.
– Many fields are inherited from parent to child
nodes in DASH.
– For example, a BaseURL can be defined in the
<MPD> node and all <Representation> nodes
inherit that value.

39. DashHandler.js
• Responsible for deciding which fragment URL should be
loaded.
• Methods:
 getInitRequest(quality) – Returns an initialization
request for a given quality, if available.
 getSegmentRequestForTime(time, quality) – Returns
a fragment URL to load for a given quality and a given
time. Returns a Stream.vo.SegmentRequest object.
 getNextSegmentRequest(quality) – Returns the next
fragment URL to load. Assumes that
getSegmentRequestForTime() has already been called.
 getCurrentTime (quality) – Returns the time for the
last loaded fragment index.

40. DashHandler.js (cont’d)
• Uses available information in the manifest (SegmentList,
SegmentTemplate, SegmentBase).
• When using a single, non-fragmented mp4 file the SIDX box
will be loaded to determine byte ranges for segments.

41. Flow
1. Create the Context and MediaPlayer instances.
var context = new Dash.di.DashContext(),
player = new MediaPlayer(context);
2. Initialize MediaPlayer and set manifest URL.
player.startup();
player.setIsLive(false);
player.attachSource(manifest_url);
3. Attach HTML Video element.
video = document.querySelector(".dash-video-player
video"),
player.autoPlay = true;
player.attachView(video);

42. 2. Call play()on the MediaPlayer (if autoPlay =
false).
3. The Stream object will be created and initialized with the
manifest URL.
4. The manifest is loaded and then parsed.
5.MediaSource, SourceBuffers, and
BufferControllers are created.
– Create one BufferController per stream type (usually
video and audio).
6. Set the duration of the MediaSource to the duration of the
manifest (or infinity for a live stream).
7. If the stream is live, calculate the live edge.
8. Call play() on the HTML video element.
9. The BufferManager instances create a timer. When the
timer ticks the state of the buffers is checked.

43. BufferManager.validate()
1. Check to see if the buffers need more data.
• Must be in a playing state.
• Must not already be loading data.
• Must require more data to be buffered.
amountBuffered < manifest.minBufferTime
2. If automatic ABR is enabled check to see if the bitrate
should be changed.
• Ask AbrController for the new quality.
• Rules will determine which bitrate to change to.
3. If initial playback, seeking, or the bitrate has changed load
the initialization fragment (if available).

44. 4. Ask the IndexHandler for the next fragment request.
• If seeking pass the seek time to the IndexHandler.
• Otherwise ask for the ‘next’ fragment.
• Pass the bitrate to the IndexHandler.
6. The IndexHandler returns a SegmentRequest indicating
what action the BufferManager should take next.
• “download” – Download and append the fragment to the buffer.
• “stall” – Wait because the IndexHandler is not ready.
• “complete” – Signal that the stream has completed playback.
7. Repeat.

45. Resources
• DASH Industry Forum
– http://www.dashif.org
– Test Vectors
– Reference Player
(http://dashif.org/reference/players/javascript)
• Reference Player Source Code
– https://github.com/Dash-Industry-Forum/dash.js
• Twitter
– @jefftapper
– @digitalprimates

46. Questions?