Silverlight Wireshark Analysis

Silverlight smooth streaming
Wireshark analysis

Yossi Cohen
DSP-IP

Fast Forward Your Development www.dsp-ip.com

SILVERLIGHT INTRODUCTION


Smooth Streaming

• Microsoft’s implementation of HTTP-based
adaptive streaming
• A hybrid media delivery method that acts like
streaming but is in fact a series of short
progressive downloads
• Leverages existing HTTP caches
• Client can seamlessly switch video quality and bit
rate based on perceived network bandwidth and
CPU resources


Streaming or Progressive Download?
Traditional Progressive
Streaming Download
• Responsive User • Works from a
Experience Web Server
• Bandwidth Use • World-wide
• User Tracking scale w/HTTP

Challenges Challenges
• No cache-ability • Limited User
• Separate, Experience
smaller • User tracking
streaming • Bandwidth Use
networks (20% watched)


Smooth Streaming Design
• Smooth Streaming File Format based on MP4
(ISO Base Media File Format)
• Video is encoded and stored on disk as one
contiguous MP4 file
▫ Separate file for each bit rate
• Each video Group of Pictures (GOP) is stored in a
Movie Fragment box
▫ This allows easy fragmentation at key frames
• Contiguous file is virtually split up into chunks
when responding to a client request


Content Provider Benefits
• Cheaper to deploy
▫ Can utilize any generic HTTP caches/proxies
▫ Doesn’t require specialized servers
at every node
• Better scalability and reach
▫ Reduces “last mile” issues because it can
dynamically adapt to inferior network conditions
• Audience can adapt to the content, rather than
requiring the content providers to guess which bit
rates are most likely to be accessible to their
audience


End User Benefits
• Fast start-up and seek times
▫ Start-up/seeking can be initiated on the lowest bit
rate before moving up to a higher bit rate
• No buffering, no disconnects, no
playback stutter
▫ As long as the user meets the minimum
bit rate requirement
• Seamless bit rate switching based on network
conditions and CPU capabilities.
• A generally consistent, smooth
playback experience


Evolution
• Previous versions of MS streaming divide the file
into many chunkc 0001.vid 0002.vid etc
• Problematic in caching, CDNs, CMS etc
• Today all fragments of a file are contained in a
single bitstream container. Typically 1 fragment
= 1 video GOP.


SILVERLIGHT FILES

Containers & Configuration files


Format options
• ASF/WMV – native Microsoft Format
• MPEG4 File-Format
• AVI
• OGG


MP4 over ASF file format
• MP4 is a lightweight container format with less
overhead than ASF
• MP4 is easier to parse in managed (.NET) code
• MP4 is based on a widely used standard, making
3rd party adoption and support easier
• MP4 has native H.264 video support
• MP4 was designed to natively support payload
fragmentation within the file


MP4 File format
• MP4 has two format types
▫ Disk Format - for file storage
▫ Wire format - for transport
• Wire format enables easy CDN support and
integration


Smooth Streaming File Format


Smooth Streaming Wire Format


File extensions
• Media Files
▫ *.ismv - Audio & Video
▫ *.isma – Audio only
• Manifest Files
▫ *.ism – Server manifest. Describes to the server
Relation between tracks, bitrates & files on disk.
Based on SMIL 2.0 XML format specification
▫ *.ismc – Describes to the client the available
streams, CODECS used, bitrates encoded, video
resolutions, markers, captions. First file delivered
to client. It’s the first file delivered to client (“SDP”
like).

Directory Structure
Media file in
different
Manifest Files bitrates


Manifest files
• VC-1, WMA, H.264 and AAC codecs
• Text streams
• Multi-language audio tracks
• Alternate video & audio tracks (i.e. multiple
camera angles, director’s commentary, etc.)
• Multiple hardware profiles (i.e. same bitrates
targeted at different playback devices)
• Script commands, markers/chapters, captions
• Client manifest Gzip compression
• URL obfuscation
• Live encoding and streaming


ISM file sample
<?xml version="1.0" encoding="utf-16" ?>
- 
- <smil xmlns="http://www.w3.org/2001/SMIL20/Language">
- <head>
<meta name="clientManifestRelativePath" content="NBA.ismc" />
</head>
- <body>
- <switch>
- <video src="NBA_3000000.ismv" systemBitrate="3000000">
<param name="trackID" value="2" valuetype="data" />
</video>
</video>
</video>

ISM file sample
</video>
</video>
</video>
- <audio src="NBA_3000000.ismv" systemBitrate="64000">
</audio>
</switch>
</body>
</smil>


*.ISMC sample
<?xml version="1.0" encoding="utf-16" ?>
- 
- <SmoothStreamingMedia MajorVersion="1" MinorVersion="0"
Duration="4084405506">
- <StreamIndex Type="video" Subtype="WVC1" Chunks="208"
Url="QualityLevels({bitrate})/Fragments(video={start time})">
<QualityLevel Bitrate="3000000" FourCC="WVC1" Width="1280" Height="720"
CodecPrivateData="250000010FD3FE27F1678A27F859E80C9082DB8D44A9
C00000010E5A67F840" />
CodecPrivateData="250000010FD3FE20F1278A20F849E80C9082493DEDDC
C00000010E5A67F840" />
CodecPrivateData="250000010FCBF81A70EF8A1A783BE80C908236EE52654
00000010E5A67F840" />
CodecPrivateData="250000010FCBE813F0AF8A13F82BE80C9081A7ABF704
400000010E5A67F840" />

SILVERLIGHT SESSION

Initiation and Flow


Smooth Streaming Protocol

• Smooth Streaming Protocol uses HTTP
[RFC2616] as its underlying transport .
• The Server role in the protocol is stateless
▫ Enabling (potentially) different instance of the
server to handle client requests
▫ Request can utilize any generic HTTP
caches/proxies - > Lowering CDN costs


Messages
• Smooth Streaming Protocol uses 4 different
messages:
▫ Manifest Request
▫ Manifest Response
▫ Fragment Request
▫ Fragment Response

• All messages follow the HTTP/1.1 specification


Messages Flow
Server Client
Manifest Request

Manifest Response

Fragment Request

Fragment Response

Fragment Request(s)


Messages
• Manifest Request and Fragment Request
message MUST use the HTTP "GET" method,
generated by the client.

• Manifest Request and Fragment Request
message use the HTTP Response messages.
Status-Code SHOULD be 200.


Smooth Streaming Transport
Protocol Session Details
Manifest Request
Manifest Response
Video Fragment Request

Audio Fragment Request
Fragment Response


Session Details - Manifest Request

• In order to initiate a presentation the Client
MUST send the server a Manifest Request using
the HTTP GET method.


Session Details - Manifest Response

• The Response is a ISMC Manifest file describing the session.
- <SmoothStreamingMedia MajorVersion="1" MinorVersion="0" Duration="5965419999">
- <StreamIndex Type="video" Subtype="WVC1" Chunks="299" Url="QualityLevels({bitrate})/Fragments(video={start time})">
CodecPrivateData="250000010FD3BE27F1678A27F859E804508253EBE8E6C00000010E5AE7F840" />
…..
<c n="0" d="20000000" />
<c n="1" d="20000000" />
.....
<c n="297" d="20000000" />
<c n="298" d="5000001" />
</StreamIndex>
- <StreamIndex Type="audio" Subtype="WmaPro" Chunks="299" Url="QualityLevels({bitrate})/Fragments(audio={start time})">
<QualityLevel Bitrate="64000"
WaveFormatEx="6201020044AC0000451F0000CF05100012001000030000000000000000000000E00042C0" />
<c n="0" d="20433560" />
....
<c n="297" d="20433560" />
<c n="298" d="4393197" />
</StreamIndex>
</SmoothStreamingMedia>


Manifest Response reviewed
• We can see in the ISMC file that the server can support 8 different levels
of quality (bitrate) for the client can chose from between 2.75Mbit to
0.35 Mbit.
- <SmoothStreamingMedia MajorVersion="1" MinorVersion="0" Duration="5965419999">
- <StreamIndex Type="video" Subtype="WVC1" Chunks="299" Url="QualityLevels({bitrate})/Fragments(video={start time})">
CodecPrivateData="250000010FD3BE27F1678A27F859E804508253EBE8E6C00000010E5AE7F840" />
CodecPrivateData="250000010FD3BE20F1278A20F849E80450823E414DD1400000010E5AE7F840" />
CodecPrivateData="250000010FCBAE1A70EF8A1A783BE8045081AE62F3F7400000010E5AE7F840" />
CodecPrivateData="250000010FCBA215F0C78A15F831E8045081A27BD635C00000010E5AE7F840" />
CodecPrivateData="250000010FCB9A11F09F8A11F827E804508199C94077400000010E5AE7F840" />
CodecPrivateData="250000010FCB920DF07F8A0DF81FE804508113396020C00000010E5AE7F840" />
CodecPrivateData="250000010FC38E0B70678A0B7819E80450810E5747B6C00000010E5AE7F840" />
CodecPrivateData="250000010FC38A09F0578A09F815E80450808AADEACF400000010E5AE7F840" />


Manifest Response – reviewed
• The client also receives the number of chunks for audio and video tracks
and the duration of each chunk so it can request the chunk which fits the
desired position in the file
<c n="0" d="20000000" />
<c n="1" d="20000000" />
<c n="2" d="20000000" />
<c n="3" d="20000000" />
....
<c n="297" d="20000000" />
<c n="298" d="5000001" />
</StreamIndex>
- <StreamIndex Type="audio" Subtype="WmaPro" Chunks="299" Url="QualityLevels({bitrate})/Fragments(audio={start time})">
<QualityLevel Bitrate="64000"
WaveFormatEx="6201020044AC0000451F0000CF05100012001000030000000000000000000000E00042C0" />
<c n="0" d="20433560" />
<c n="1" d="19969161" />
<c n="2" d="19969161" />
<c n="3" d="20433560" />
<c n="4" d="20433560" />
<c n="297" d="20433560" />
<c n="298" d="4393197" />
</StreamIndex>
</SmoothStreamingMedia>


Session Details – Fragment Request

• Client-Server requests are based on RESTFull URLs:
GET /mediadl/iisnet/smoothmedia/Experience/BigBuckBunny_720p.ism/QualityLevels(350000)/Fragments(video=0)

• The URL includes reference to:
▫ Bitrate as QualityLevels which maps to a media file
▫ Fragment number


Session Details – Fragment Response

• The Server:
▫ checks “BigBuckBunny_720p.ism” server manifest file to find the
media file associated with the quality level(350000)
▫ Opens and parses the associated media file to get the chunk with
requested time offset (0).
▫ Sends the requested media fragment to the client as HTTP
response with status code set to 200


DSP-IP Contact information
For Course materials licensing & lecture request contact:
Adi Yakov
Training and Courses Manager
adi@dsp-
adi@dsp-ip.com
+972-9-8651933
972-
For projects development services contact:
Alona Ashkenazi
Technology Management Services :
alona@dsp-
alona@dsp-ip.com
+972-
+972-9-8850956 www.dsp-ip.
www.dsp-ip.com
Mail : info@dsp-ip.com
info@dsp-ip.
Phone: 972- 8850956,
Phone: +972-9-8850956,
Fax : +972-50- 8962910
972-50-


Refrences
• Most valuable refrence:
http://alexzambelli.com/blog/2009/02/10/smo
oth-streaming-architecture/


DSP-IP Contact information
For Course materials licensing & lecture request contact:
Adi Yakov
Training and Courses Manager
adi@dsp-
adi@dsp-ip.com
+972-
+972-9-8651933
For projects development services contact:
Alona Ashkenazi
Technology Management Services :
alona@dsp-
alona@dsp-ip.com
+972-
+972-9-8850956 www.dsp-ip.
www.dsp-ip.com
Mail : info@dsp-ip.com
info@dsp-ip.
Phone: 972- 8850956,
Phone: +972-9-8850956,
Fax : +972-50- 8962910
972-50-


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