Constant Bit Rate

• Constant Bit Rate

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iTunes - File format support

1 The latest version of iTunes (Win/Mac) supports importing audio CDs with the default iTunes standard file format of AAC at 256 kbit/s, but users can choose from 16 kbit/s to

320 kbit/s constant bit rates (CBR) in either AAC or MP3


Telecommunication - Telephone

1 This is important because telephone calls can negotiate a contract so as to guarantee themselves a constant bit rate, something that will ensure a caller's voice is not delayed in parts

or cut-off completely


Packet switching - Overview

1 Packet switching contrasts with another principal networking paradigm, circuit switching, a

method which sets up a limited number of dedicated connections of constant bit rate and constant delay

between nodes for exclusive use during the communication session


Asynchronous Transfer Mode - Cells in practice

1 AAL1 is used for constant bit rate

(CBR) services and circuit emulation


Time-division multiplexing - History

1 Each byte represented a single telephone call encoded into a constant bit rate signal of 64

kbit/s


MP3 - Audio quality

1 Using a constant bit rate makes encoding simpler and faster


MP3 - CBR

1 Early MPEG Layer III encoders used what is now called Constant Bit Rate (CBR). The software was only able to use a uniform bitrate on all frames in

an MP3 file.


Rhapsody (online music service) - Rhapsody MP3

1 In addition to its subscription service, Rhapsody sells 256 kbit/s constant

bit rate MP3s individually.


Video CD - XVCD

1 A normal VCD is encoded to MPEG-1 at a constant bit rate (CBR), so all scenes are required to use exactly the same data rate, regardless of

complexity


Optical disc drive - Rotational mechanism

1 It was a feature important for streaming sound|audio data that

always tend to require a constant bit rate


Digital video - Constant bit rate versus variable bit rate

1 As noted above BPP represents the average bits per pixel. There are

compression algorithms that keep the BPP almost constant throughout the

entire duration of the video. In this case we also get video output with a Constant bitrate|constant bit rate (CBR). This CBR

video is suitable for real-time, non-buffered, fixed bandwidth video

streaming (e.g. in videoconferencing).


Multiplexer - Telecommunications

1 In telecommunications and signal processing, an analog time division multiplexing|time

division multiplexer (TDM) may take several samples of separate analogue signals and combine them into one wide-band analog signal. Alternatively, a digital TDM may

combine a limited number of constant bit rate digital data streams into one data

stream of a higher data rate, by forming Frame (networking)|data frames consisting of

one timeslot per channel.


Asynchronous communication - Data link layer and higher

1 Asynchronous communication at the data link layer or higher protocol layers is

known as statistical multiplexing or packet mode communication, for example

asynchronous transfer mode (ATM). In this case the asynchronously transferred blocks are called data packets, for example ATM

cells. The opposite is circuit switched communication, which provides constant

bit rate, for example ISDN and SONET/SDH.


Asynchronous communication - Application layer

1 An asynchronous communication service or application does not

require a constant bit rate. Examples are file transfer, email and the World

Wide Web. An example of the opposite, a synchronous

communication service, is realtime streaming media, for example IP

telephony, IP-TV and video conferencing.


DTS (sound system) - DTS-HD High Resolution Audio

1 DTS-HD High Resolution Audio is selected as an optional surround

sound format for Blu-ray Disc and HD DVD, with constant bit rates up to

6.0 Mbit/s and 3.0 Mbit/s, respectively


Dolby Digital - Dolby Digital in the cinema

1 A constant bit rate of 320 kbit/s is used


Windows Media Video

1 The first version of the codec, WMV 7, was introduced in 1999, and was built upon Microsoft's implementation of MPEG-4 Part 2.[

http://digitalcontentproducer.com/mag/video_mpeg_makes_scene/ MPEG-4 makes the scene] Continued proprietary development led to newer

versions of the codec, but the bit stream syntax was not frozen until WMV 9.[ http://download.microsoft.com/download/6/f/c/6fc03c60-5d5b-42c0-bcce-5e184fa56741/2_Audio_Video.ppt Windows Media Audio Video 9 Series] While all versions of WMV support variable bit rate, average bit

rate, and constant bit rate, WMV 9 introduced several important features including native support for interlaced video, non-square pixels, and

motion interpolation|frame interpolation.[ http://www.microsoft.com/windows/windowsmedia/demos/video_quality_de

mos.aspx Microsoft Windows Media - Demos Video Quality] WMV 9 also introduced a new profile titled Windows Media Video 9 Professional,

[ http://www.elims.org/downloads/sample_content/9Series_RevGuide.pdf Windows Media 9 Series Beta Reviewer's Guide] which is activated

automatically whenever the video resolution exceeds 300,000 pixels (e.g., 528x576, 640×480 or 768x432 and beyond) and the bitrate 1000kbit/s


Windows Media Audio - Windows Media Audio Voice

1 Encoding is limited to constant bit rate (CBR) and up to

20kbit/s


Virtual circuit

1 Virtual circuit communication resembles circuit switching, since

both are connection oriented, meaning that in both cases data is

delivered in correct order, and signalling overhead is required

during a connection establishment phase. However, circuit switching

provides constant bit rate and latency, while these may vary in a virtual circuit service due to factors

such as:


Virtual circuit - Layer 2/3 virtual circuits

1 * Bandwidth reservation during the connection establishment phase is

supported, making guaranteed Quality of Service (QoS) possible. For

example, a constant bit rate QoS class may be provided, resulting in

emulation of circuit switching.


Dirac (video compression format) - Technology

1 Dirac supports both constant bit rate and variable bit rate operation. When the low delay syntax is used, the bit rate will be constant for each area (Dirac slice) in a picture to ensure constant latency. Dirac supports lossy and lossless compression

modes.


Dolby Digital - In the cinema

1 A constant bit rate of 320 kbit/s is used


Constant bitrate

1 When referring to codecs, constant bit rate encoding means that the rate

at which a codec's output data should be consumed is constant


Virtual connection

1 Virtual circuit communication resembles circuit switching, since

both are connection oriented, meaning that in both cases data is

delivered in correct order, and signalling overhead is required

during a connection establishment phase. However, circuit switching provides a constant bit rate and

latency, while these may vary in a virtual circuit service due to factors

such as:


Windows Media Video (video compression format)

1 The first version of the format, WMV 7, was introduced in 1999, and was built upon Microsoft's implementation of MPEG-4 Part

2.[http://digitalcontentproducer.com/mag/video_mpeg_makes_scene/ MPEG-4 makes the scene] Continued proprietary development led to newer versions of

the format, but the bit stream syntax was not frozen until WMV 9.[http://download.microsoft.com/download/6/f/c/6fc03c60-5d5b-42c0-bcce-

5e184fa56741/2_Audio_Video.ppt Windows Media Audio Video 9 Series] While all versions of WMV support variable bit rate, average bit rate, and constant

bit rate, WMV 9 introduced several important features including native support for interlaced video, non-square pixels, and motion interpolation|frame

interpolation.[http://www.microsoft.com/windows/windowsmedia/demos/video_quality_demos.aspx Microsoft Windows Media - Demos Video Quality]

WMV 9 also introduced a new profile titled Windows Media Video 9 Professional,[http://www.elims.org/downloads/sample_content/9Series_RevGui

de.pdf Windows Media 9 Series Beta Reviewer's Guide] which is activated automatically whenever the video resolution exceeds 300,000 pixels (e.g.,

528x576, 640×480 or 768x432 and beyond) and the bitrate 1000kbit/s


TwinVQ - TwinVQ as a proprietary audio format

1 TwinVQ uses Twin vector quantization. The proprietary TwinVQ codec supports constant bit rate code|encoding at 80, 96, 112, 128,

160 and 192 kbit/s. It was claimed that TwinVQ files are about 30 to 35% smaller

than MP3 files of adequate quality. For example, a 96 kbit/s TwinVQ file allegedly

has roughly the same quality as a 128 kbit/s MP3 file. The higher quality is achieved at

the cost of higher processor usage.


RealVideo - Technology

1 To facilitate real-time streaming, RealVideo (and RealAudio) normally uses constant bit rate encoding, so

that the same amount of data is sent over the network each second


Traffic contract - Constant Bit Rate (CBR)

1 The CBR service category is used for connections that transport traffic at a constant bit rate, where there is an

inherent reliance on time synchronisation between the traffic

source and destination


Virtual Path Identifier - Cells in practice

1 ATM supports different types of services via AALs. Standardized AALs include AAL1, AAL2,

and AAL5, and the rarely used AAL3 and AAL4. AAL1 is used for constant bit rate (CBR)

services and circuit emulation. Synchronization is also maintained at AAL1. AAL2 through AAL4

are used for variable bit rate (VBR) services, and AAL5 for data. Which AAL is in use for a

given cell is not encoded in the cell. Instead, it is negotiated by or configured at the endpoints

on a per-virtual-connection basis.


ATM adaptation layer

1 will meet a variety of needs. The classification is based on whether a

timing relationship must be maintained between source and

destination, whether the application requires a constant bit rate, and

whether the transfer is connection oriented or connectionless.


ATM adaptation layer

1 *'ATM Adaptation Layer 1|AAL Type 1' supports constant bit rate (CBR), synchronous, connection oriented traffic. Examples include T1 (DS1),

E1, and x64 kbit/s emulation.


WMV - Windows Media Video

1 The first version of the format, WMV 7, was introduced in 1999, and was built upon Microsoft's implementation of MPEG-4 Part

2.[http://digitalcontentproducer.com/mag/video_mpeg_makes_scene/ MPEG-4 makes the scene] Continued proprietary development led to newer versions of

the format, but the bit stream syntax was not frozen until WMV 9.[http://download.microsoft.com/download/6/f/c/6fc03c60-5d5b-42c0-bcce-

5e184fa56741/2_Audio_Video.ppt Windows Media Audio Video 9 Series] While all versions of WMV support variable bit rate, average bit rate, and constant

bit rate, WMV 9 introduced several important features including native support for interlaced video, non-square pixels, and motion interpolation|frame

interpolation.[http://www.microsoft.com/windows/windowsmedia/demos/video_quality_demos.aspx Microsoft Windows Media - Demos Video Quality]

WMV 9 also introduced a new profile titled Windows Media Video 9 Professional,[http://www.elims.org/downloads/sample_content/9Series_RevGui

de.pdf Windows Media 9 Series Beta Reviewer's Guide] which is activated automatically whenever the video resolution exceeds 300,000 pixels (e.g.,

528x576, 640×480 or 768x432 and beyond) and the bitrate 1000kbit/s


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Constant Bit Rate