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33 Cards in this Set
- Front
- Back
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Aim of Web |
To provide searchable, immediately available network content |
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Provision of video over the Internet |
4 main categories: Downloadable file Progressive Download Realtime Streaming Multicasting |
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Downloadable File |
Simplest method of providing video on the web Uses a file transfer protocol to download the file This cannot provide real-time playback during the download Quality is guaranteed and not dependent on bandwidth The only restriction is how long the user is prepared to wait for the download to finish |
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Progressive Download |
Served from standard Web and FTP servers using lossless transfer protocols This means that all the video is guaranteed to arrive, but we can not predict how long it will take Progressive download systems can start playing the file before it is fully downloaded Often called HTTP streaming or Pseudo streaming |
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Progressive using HTTP |
Any HTTP streamed content is simply a file that is streamed and started as soon as possible In theory playing won't catch up with downloading, if it does, the movie will stop until more data is received |
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Progressive download - Capabilities |
User can navigate through any of file that has been downloaded Simple to set up and very good when used with a limited number of viewers or a powerful web sever |
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Progressive Download - faults |
Has no mechanism for varying the download quality basde on the bandwidth of the users connection Thus often have to provide several quality/sizes of downloadable file for the user |
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Real-Time Streaming |
A technique for transferring data such that it can be processed as a steady and continuous stream RTS should provide random access to the whole file so the user can fast-forward or rewind Requires a dedicated streaming server |
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Real-Time Streaming - Process |
The multimedia data arrives, is briefly buffered before being played and is then discarded the whole file is never actually stored on the users computer Every time the play head is moved the video will have to rebuffer |
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Streaming Components |
Players, Encoders, Servers Compatible codecs Compatible File-format Compatible Protocols |
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Encoders |
Many video editing applications enable the creation of video in suitable streaming formats Final Cut Pro QuickTime Premier |
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Servers |
A streaming media server is an application which runs on an internet server provide the ability to handle large traffic loads Can detect users' connection speeds enable the broadcast of live events |
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Players |
Different formats have their own players |
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Application Protocols |
A common application level protocol that canbe used for real-time streaming of video media is the Real-Time streaming protocol (RTSP) |
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RTSP |
is a client-server multimedia presentation control protocol originated by RealNetworks The protocol is similar in syntax and operation to HTTP but RTSP adds new functionality |
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Streaming with RTSP |
The sending of the actual streaming data itself is not part of the TRSP protocol, but it acts as a control mechanism to handle client requests such as pause, fast forward, reverse, and absolute positioning |
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RTSP transporting |
Most RTSP servers use real-time transport protocol (RTP) as the transport protocol for the actual audio/video data |
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RTP |
A standardized packet format for delivering audio and video over the internet Similar to TCP, but for audio and video data and without the guaranteed delivery mechanism |
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RTP services |
Data identification - Indication of what kind of content is being carried Sequence Numbering Time stamping - to allow synchronization Delivery monitoring The protocol does not ensure delivery or provide quality of service guarantees |
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Real-time Streaming - packets |
Breaks data into many packets sized according to the bandwidth available between client and server When enough packets have been received by the client the users software can be: Playing one packet Decompressing another downloading the third |
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Real-time Streaming - principles |
A streamed clip will be instantly viewable, with few or no interruptions, but it's video quality may be lower than progressive download Clips are streamed at the same time they are being viewed Quality may vary, but clip should not stop playing |
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Ream-time Streaming - advantages |
Random access and "live" streaming Progressive download does not allow you to randomly jump to any position It is also difficult to stream a live performance using progressive download |
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Formats |
Protocols like RTSP are necessary but not sufficient to achieve end-to-end interoperability formats like ASF (.wmv), QuickTime (.mov) and RealMedia(.rm) act as containers for multimedia data |
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File Formats |
You need to pick one or more file formats suitable for your end viewers |
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Most common streaming file formats |
Windows Media RealMedia QuickTime AdobeFlash |
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Streaming Frameworks |
Many companies provide all the components needed to encode, serve and view streaming media RealVideo QuickTime Adobe Flash |
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RealNetworks |
The RealMedia format includes a multiple Bit Rate (MBR) implementation called SureStream up to 8 baseline copies of the media can be made, all varying data and frame rates RealProducer uses SureStream to encode the digital media for streaming |
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QuickTime |
offers smart streaming, a similar idea to SureStream Enables switching between multiple versions of the encoded bandwidth to respond to changes in the users real world bandwidth |
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Windows Media ASF |
Advanced Streaming Format , a streaming multimedia file format developed by microsoft Provides codecs for set bandwidths and automatic streaming originally using the microsoft media server (MMS) protocol and now using RTSP |
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Streaming Live Content |
Most streaming content is streamed from pre-recorded media files However, live content can often have greater impact than pre-recorded on demand content Streaming live content requires a steaming media server |
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Multicasting |
Real-time streaming to multiple recipients who all view the same content at the same time Requires used to "tune in" for a particular multicast which is only available to them |
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Multicasting - Process |
Normal Internet traffic needs separate connections for each source-destination pair, IP Multicasting allows many recipients to share the same source This means that just one set of packets is transmitted for all the destinations |
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Multicasting - pros |
Provides one to many communication over an IP infrastructure Source sends a packet only once, even if it needs to be delivered to a large number of receivers The nodes in the network take care of replicating the packet to reach multiple receivers only where necessary |
