IPTV, VOD, Multicasting and MPEG infrastructure

Week 9 - Enabling Technology

In general, humans experience the world analogically, for example vision is an analog experience

because smooth gradations of shapes and colors is perceived infinitely

Analog format information is transmitted by modulating a continuous transmission signal for

example amplifying a signals strength or varying its frequency to add or take away data. Sound

vibrations from telephones are converted into electrical vibrations before they are transmitted over

traditional telephone lines.

Radio wave transmissions work in the same way. Modems are required for computers, to turn

signals from digital to analogwhich handles data in digital form. Before transmitting the signals over

communication lines such as telephone lines which carry only analog signals, the signals are

converted back to digital format the receiving end enabling computersto process the data in its

digital format; this is referred as “demodulated”.

• w3c and Internet authorities (isoc&ietf)

The Internet is controlled by a loosely organized international collaboration of autonomous, interconnected networks. They support host to host communication through voluntary close attachment to open protocols and procedures defined by Internet Standards.

in order to operate on the InternetCertain protocols and parameters are required.

A number of bodies have become responsible for those protocol standards and parameters.

Almost all Internet technological standards are developed and set by the group consisting of the Internet Society (ISOC) and the units operating under the auspices of ISOC: the Internet Architecture Board (IAB), the Internet Engineering Steering Group (IESG), the Internet Engineering Task Force (IETF), the Internet Research Steering Group (IRSG), the Internet Research Task Force (IRTF), and the RFC Editor. ISOC allows them a large degree of independence in their technical work, while these units are responsible to ISOC.

Internet domain names and IP addresses are governed by administrators of the Internet Corporation for assigned names and numbers (ICANN) and it’s Internet Assigned Numbers Authority (IANA).

World Wide Web standards are developed by the World Wide Web Consortium (W3C).

H.264/MPEG-4 AVC is a block oriented motion-compensation (algorithmic technique to encode video data for video compression) based video compression standard developed by the ITU-T Video Coding Experts Group.

H.264 is well known as being one of the video encoding standards for Blu-ray Discs. All Blu-ray Disc players must be able to decode H.264. H.264 is also widely used by streaming internet sources, such as videos from Vimeo, YouTube, iTunes Store, web software such as the Adobe Flash Player and Microsoft Silverlight. H.264 is also used in various HDTV broadcasts over terrestrial (ATSC, ISDB-T, DVB-T or DVB-T2), cable (DVB-C), and satellite (DVB-S and DVB-S2). H.264 is typically a lossy compression, but it is possible to create lossless encodings with H.264.

Rich media formats

Before a entire file has been transmitted, a client media player can begin playing the data for example a film. Distinguishing delivery method from the media distributed applies specifically to telecommunications networks as most other delivery systems are either inherently streaming such asradio, television or inherently nonstreaming such as, books, video cassettes, audio CDs. In modern days Internet television is a common form of streamed media. The term "streaming media" can apply to media other than video and audio such as live closed captioningand real time text. These media are all considered "streaming text". The term "streaming" was first used in the early 1990s as a better description for video on demand on IP networks. At the time such video was usually referred to as "store and forward video"

Content delivered live over the Internet is referred as”Live streaming”, which cameras arerequires for the media. Live Streaming also requires anencoder to digitize the content. A media publisher andcontent delivery network is used to distribute and deliver the content.

Around 2002 the streaming format and the widespread adoption of Adobe Flashassisted the development of a video streaming format through Flash which is the format used in Flash based players on many popular video hosting sites such as YouTube. Increasing consumer demand for live streaming has prompted YouTube to implement a new live streaming service to users

A broadband speed of 2.5 Mbit/s or more is recommended for streaming videos.

using the following formula streaming media storage size can be calculated from the streaming bandwidth and length of the media.

storage size (in megabytes) = length (in seconds) × bit rate (in bit/s) / (8 × 1024 × 1024)

Real world example:

One hour of video encoded at 300 kbit/s (this was a typical broadband video in 2005 and it was usually encoded in a 320 × 240 pixels window size) will be

Compression

JPEG is seen commonly with the .jpgextension which is also a commonly used method of lossy compression for digital images. Images which are produced by digital photography, the level of compression can be adjusted, allowing the options between storage size and image quality. JPEG typically achieves the ratio of 10:1 compression with low perceptible loss in image quality.

JPEG compression is used in a number of image file formats. Digital cameras most commonly use JPEG/Exif image format which are used by and other photographic image capture devices. JPEG/JFIFis the most common format for storing and transmitting photographic images on the internet.

JPEG/JFIF supports a maximum image size of 65535×65535

The JPEG standard specifies the codec which defines how an image is compressed into a stream of bytes and decompressed back into an image The Exif and JFIF standards define the commonly used file formats for theexchange of JPEG compressed images.

• Joint Photographic Experts Group (JPEG)

Still images

• Moving Picture Experts Group (MPEG)

Advanced Graphics Port

A advanced graphics port is designed for Video cards and 3D accelerators. It was originally designed by Intel and introduced in August of 1997. AGP introduces a dedicated point to point channel which allows the graphics controller to directly access the system memory.

This is an AGP slot integrated on amotherboard.

The AGP channel is 32-bits wide and runs at 66 MHz whichtransforms to a total bandwidth of 266 MBps.AGP has a much higher bandwidth than the PCI bandwidth which is only 133 MBps. AGP also

supports two optional faster modes throughput of 533 MBps and 1.07 GBps. AGP allows 3D textures to be stored in main memory rather than video memory.

Each computer with AGP support will either have one AGP slot or onboard AGP video. Users can have one AGP video card and one PCI video card or use a motherboard which supports SLI. SLI is Short for Scalable Link Interface which was developed byNVIDIA technology. SLI allows two video cards which support SLI to share the workload, increasing the overall performance

AGP is available in three different versions, the original AGP, AGP 2.0introduced in May 1998, and AGP 3.0 (AGP 8x) introduced in November 2000. AGP 2.0 added 4 times faster signaling capable of operating at 1.5V. When AGP 3.0 was launched,the capabilitywas doubled to 3.0Vtransfer speeds.

Video Capture

• Analogue to-Digital Conversion (A-to-D)

An analog to digital converter is any device which converts analog signals in continuous quantity into digital signals. Their is a need for conversion from analog to digital as analog signal is a continuous successful wave form of curves which cannot be read by a computer. Data can be amplified and added or taken from the original signal by converting the analog signal.

the value of the input analog signal is a standard thereby the converter will know if the input warrants is a high or low signal. The amplitude or volume is measured constantly In audio digital conversion. The output is a list of binary data containing the sound wave values. Most of the conversion is typically done by only a single chip.

The signals are often in electrical form for example in a modem or cable TV. Phone line or cable signals are analog. The modem extracts the original signal and converts it into digital signals to address the computer or the digital TV.

• Analogue format

As continuous variable physical quantities analog format describes a device or system which represents changing values. Generally analog devices have a clock in which the hands move continuously around the face.

a digital clock is capable of executing with an limitation in which every tenth of a second.

YUV

Y is black & white luminance

U is blue - Y

V is red – Y human eye is very sensitive to blue and red.

A lot of compressions ae built on YUV.

Used for small storage and bandwidth requirement

• Digital format

Digital video formats are captured and stored in a digital format as ones and zeros rather than a series of still pictures captured in film and digital versus analog signals are used. To allow easy manipulation by computers, information is processed and stored as a sequence of digital data however the video is still displayed through the screen in analog form.

Digital video is composed of a series of bitmap (BMP) images displayed in constant rapid succession with common frequencies of 15, 24, 30 and 60 frames per second (FPS). The quality of movement details are captured or displayed depending upon number of frames the DV has.

good quality movies and videos are recorded and viewed at 60 FPS, while slow motion videos are taken with high speed photography equipment at more than 1,000 FPS and then viewed at standard rates.

Each BMP image or frame in the DV includes a scanning pattern of parallel lines of pixels with width and height displayed in number of pixels, known as resolution. Higher captured video resolutions have higher clarity and quality.

DVD Physical Formats

• DVD 5

Single sided, single layer with capacity of up to 4.7 GB

• DVD 9

Single sided, dual-layered with total capacity of 8.5 GB

• DVD 10

Double-sided, single layer with a capacity of 9.4 GB

• DVD 18

A double-sided, dual-layer with total capacity of 17 GB

Compression techniques

compression techniques fall under two categories and used with digital graphics which are lossy and lossless.

both uses different techniques to compress files for the duplication of data in the graphic and for use of much more compact data representation.

Different results are achieved by different file formats through Lossy and Lossless which each have various methods. Not all lossy or lossless formats use the same methods. In digital Imaging, Bitmaps covers compression methods in more detail. Lossy compression methods include DCT (Discreet Cosine Transform), Vector Quantisation and Huffman coding

Lossless compression methods include RLE (Run Length Encoding), string table compression, LZW (Lempel Ziff Welch) and zlib.

Compression methods are known as algorithms which are calculations used to compress files. Organisations which create file formats create their own algorithms with competition on who can create the best format.

Bitmaps consist of pixels which have the same values, for example in a photograph of a setting, there will be areas of pixels whoch all have the same value. There is no need to store every single pixel. Algorithms look for redundant data, for example repeat values which are not needed which essentially creates a smaller file size but keeps the relevant data for displaying the graphic. When you look at a compressed file, no or little difference should be done in the graphic.

To save and open a file in a compressed format A CODEC (compressor/decompressor) is used carry out the algorithm. CODECs can be implemented in either hardware or software. Hardware CODECs generally cost more since use dedicated chips instead of the computers CPU time making them significantly more efficient."

• Discrete Cosine Transformation

Equate to a cosine curve

• Encoding “words” (Hofman)

Match to a “code word”

Understanding encoding

An intra frame is an image in a motion video sequence that is independently coded and has no reference to any other frames. Iframes are encoded in a way similar to JPEG for still images in MPEG other video codec such as H.263 and H.264.

In the image below, it shows how Intra frames are used in a group of pictures (GOP) as reference frames (key frames). Each Intra- frame contains a complete image which can be reference by other frames within the GOP. In this image Iframe typically requires the largest number of bytes to represent the image, in this case 200 kB.

Encoding is the process of the conversion of data into formats required for different information processing needs, including:

Encoding can have two meanings:

In computer technology, encoding is the process of applying a specific code such as letters, symbols and numbers to data for conversion into an equivalent cipher.

In electronics, encoding is the process of analog to digital conversion.

Encoding comprises the use of a code reformatting its original data so it can be used by an external process.

The most common used encoding scheme for files which contain text is the type of code used for converting characters which is known as “American Standard Code for Information Interchange” (ASCII). ASCII consists of both printable and nonprintable characters which represent uppercase and lowercase letters, symbols, punctuation marks and numbers in which a unique number is given to some characters.

Encoding is also used to reduce the size of audio and video files. Each audio and video file format has a codec program which recodes the file into the appropriate format and then decodes the file so its capable for playback.

webP compression google

Google have developed WebP which is is a new image format and supported in their browser Chrome. Also supportive in Opera and Android optimized to enable faster and smaller images on the Web.Compared to PNG and JPEG images, WebP images are about 30% smaller in size. The WebP image format features equivalence with other formats as it supports:

Lossy compression: The lossy compression is based on VP8 key frame encoding. VP8 is a video compression format.

Lossless compression: Developed by the WebP team. Transparency: 8-bit alpha channel is useful for graphical images. The Alpha channel can be used

along with lossy RGB. Animation: Supports true-colour animated images. Metadata: It may have EXIF and XMP metadata used by cameras.

Predict pixel characteristics from previous block “intra frame

Googles aim is to do a comparative evaluation based on the new encoder they released in libwebp on WebP and JPEG image compression. Running a set of easily repeatable experiments using publicly available tools and compare the image compression achieved by WebP and JPEG is googles main goal.

Thier comparative study of WebP focused on evaluating a large number of images and was used on JPEG sources.

Google have made their web pages load faster by making web images smaller. Images include 60%-65% of bytes on most web pages. Total rendering time is a major factor in page size especially for mobile devices since images smaller in size save both bandwidth and battery life.

Same procedure is used by WebP's lossy compression in which the VP8 for predicting (video) frames. block prediction is what VP8 is based on using block based codec. Frames are devided into smaller segments called macroblocks. Based on previously processed blocks redundant motion and colour information can be predicted by the encoder within each macroblock.

Only the pixels already decoded by the image frame is ‘key' in the instant current existing neighbourhood of each of the macroblocks. VP8 then tries to restore the unknown part of image frames which known as predictive coding.

The redundant data is removed from the block resulting in higher efficient compression. To transmit in a compressed form, a small difference called residual is left.

IP Multicasting

IP multicasting the communication system in which data is sent from server to a set of clients who are interested in receiving that data. Any client can forcefully enter or leave the communication.

Multicast IP address form the root of multicast communication. Since IP addresses fall under classes, it’s the Class D IP addresses used as multicast IP addresses.

Here is the structure of multicast IP address.

multicast IPs range from sequences of 224.0.0.0 to 239.255.255.255. The Multicast IP address use the known researved ports of 0-1024.

Here are some other known reseverd ports:

224.0.0.1 signifies every system on a subnet 224.0.0.2 signifies every router on a subnet

The server sends data on a specific multicast IP address for multicast communication. In order for clients to receive the data, listening on the same multicast address is required. The clients can be on various different networks.

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