Professional video over IP
Encyclopedia
Professional video over IP systems use some existing standard video codec
to reduce the program material to a bitstream
(e.g., an MPEG transport stream), and then to use an Internet Protocol
(IP) network to carry that bitstream encapsulated
in a stream of IP packets. This is typically accomplished using some variant of the RTP
protocol.
Carrying professional video
over IP networks has special challenges compared to most non-time-critical IP traffic. Many of these problems are similar to those encountered in voice over IP
, but to a much higher level of engineering requirements. In particular, there are very strict quality of service
requirements which must be fulfilled for use in professional broadcast environments.
rate caused by low-probability statistical congestion events and amplification of bit errors in the underlying hardware, most professional solutions use some kind of forward error correction
to ensure that the encoded video stream can be reconstructed even if a few packets are lost. This is typically applied at the packet level, since the encapsulated video bitstream is typically only designed to tolerate low levels of bit or burst errors, rather than the loss of whole packets. Resending packets is not an option because of the sequential nature of the underlying video signal. For live video, a resent packet would arrive well after the arrival of the next frame of video.
techniques (see below).
The remaining delay variation can be removed by buffering, at the expense of added time delay. If forward error correction is used, a small proportion of packets arriving after the deadline can be tolerated, since they can be dealt with by being discarded on receipt, and then treated in the same way as lost packets. Added time delay is particularly unwelcome in PTZ camera
s as it makes operator control difficult at values over 250ms.
more complex by making the recovery of the underlying timing of the video signal far more difficult. This is typically solved by genlock
ing both ends of the system to external station sync signals, typically generated from sources such as GPS or atomic clock
s, thus only requiring the extraction of coarse timing information at the receiving end in order to achieve high-quality video synchronization. The extraction of coarse timing data is typically done using a phase locked loop with a long time constant.
, bandwidth reservation, traffic shaping
, and traffic prioritization techniques, which require more complex network engineering, but will work when the simple approach of building a non-blocking network is not possible. See RSVP
for one approach to IP network traffic engineering.
The Pro-MPEG Wide Area Network group has done much recent work on creating a draft standard for interoperable professional video over IP.
, with a combination of IP-based cameras or analog cameras using IP-based encoders; image transmission; Storage and Retrieval, which uses technologies such as RAID array
s and iSCSI
for recorded and indexed video; and video management, which affords web browser-enabled management and control of IP-based CCTV systems.
One key advantage of IP-based CCTV is the ability to use network infastructure, providing adequate bandwidth and availability of switching and routing, rather than coaxial cabling. However, running bandwidth-intensive surveillance video over corporate data networks is a point of organizational contention, depending on the potential impact on network performance.
A class of companies produce Video Management Software to help manage capture and storage of video content. Digital video also makes possible Video Content Analysis, which allows automatic detection and identification of various kinds of objects or motion.
Also another emerging model is off-site storage of surveillance video. These online surveillance providers are utilizing cloud computing technologies to consolidate multi-site surveillance video over the web.
Manufacturers of CCTV equipment are steadily integrating IP network technology into their product portfolios.
Video codec
A video codec is a device or software that enables video compression and/or decompression for digital video. The compression usually employs lossy data compression. Historically, video was stored as an analog signal on magnetic tape...
to reduce the program material to a bitstream
Bitstream
A bitstream or bit stream is a time series of bits.A bytestream is a series of bytes, typically of 8 bits each, and can be regarded as a special case of a bitstream....
(e.g., an MPEG transport stream), and then to use an Internet Protocol
Internet Protocol
The Internet Protocol is the principal communications protocol used for relaying datagrams across an internetwork using the Internet Protocol Suite...
(IP) network to carry that bitstream encapsulated
Encapsulation (networking)
In computer networking, encapsulation is a method of designing modular communication protocols in which logically separate functions in the network are abstracted from their underlying structures by inclusion or information hiding within higher level objects....
in a stream of IP packets. This is typically accomplished using some variant of the RTP
Real-time Transport Protocol
The Real-time Transport Protocol defines a standardized packet format for delivering audio and video over IP networks. RTP is used extensively in communication and entertainment systems that involve streaming media, such as telephony, video teleconference applications, television services and...
protocol.
Carrying professional video
Video
Video is the technology of electronically capturing, recording, processing, storing, transmitting, and reconstructing a sequence of still images representing scenes in motion.- History :...
over IP networks has special challenges compared to most non-time-critical IP traffic. Many of these problems are similar to those encountered in voice over IP
Voice over IP
Voice over Internet Protocol is a family of technologies, methodologies, communication protocols, and transmission techniques for the delivery of voice communications and multimedia sessions over Internet Protocol networks, such as the Internet...
, but to a much higher level of engineering requirements. In particular, there are very strict quality of service
Quality of service
The quality of service refers to several related aspects of telephony and computer networks that allow the transport of traffic with special requirements...
requirements which must be fulfilled for use in professional broadcast environments.
Packet loss
Since even well-engineered IP networks tend to have a small residual packet lossPacket loss
Packet loss occurs when one or more packets of data travelling across a computer network fail to reach their destination. Packet loss is distinguished as one of the three main error types encountered in digital communications; the other two being bit error and spurious packets caused due to noise.-...
rate caused by low-probability statistical congestion events and amplification of bit errors in the underlying hardware, most professional solutions use some kind of forward error correction
Forward error correction
In telecommunication, information theory, and coding theory, forward error correction or channel coding is a technique used for controlling errors in data transmission over unreliable or noisy communication channels....
to ensure that the encoded video stream can be reconstructed even if a few packets are lost. This is typically applied at the packet level, since the encapsulated video bitstream is typically only designed to tolerate low levels of bit or burst errors, rather than the loss of whole packets. Resending packets is not an option because of the sequential nature of the underlying video signal. For live video, a resent packet would arrive well after the arrival of the next frame of video.
Network delay variation
Network delay variation can be kept to a minimum by using a high-speed network backbone, and ensuring that video traffic does not encounter excessive queue delays. This is typically done by either ensuring that the network is not too close to its full capacity, or that video traffic is prioritized using traffic engineeringTeletraffic engineering
Telecommunications traffic engineering, teletraffic engineering, or traffic engineering is the application of traffic engineering theory to telecommunications...
techniques (see below).
The remaining delay variation can be removed by buffering, at the expense of added time delay. If forward error correction is used, a small proportion of packets arriving after the deadline can be tolerated, since they can be dealt with by being discarded on receipt, and then treated in the same way as lost packets. Added time delay is particularly unwelcome in PTZ camera
PTZ camera
A Pan tilt zoom camera is a closed-circuit television camera with remote directional and zoom control.In television production PTZ are used with professional video cameras in television studios and referred to as camera robotics. These systems can be remotely controlled by automation systems...
s as it makes operator control difficult at values over 250ms.
Timing reconstruction
The other problem presented by latency variation is that it makes synchronizationSynchronization
Synchronization is timekeeping which requires the coordination of events to operate a system in unison. The familiar conductor of an orchestra serves to keep the orchestra in time....
more complex by making the recovery of the underlying timing of the video signal far more difficult. This is typically solved by genlock
Genlock
Genlock is a common technique where the video output of one source, or a specific reference signal from a signal generator, is used to synchronize other television picture sources together. The aim in video and digital audio applications is to ensure the coincidence of signals in time at a...
ing both ends of the system to external station sync signals, typically generated from sources such as GPS or atomic clock
Atomic clock
An atomic clock is a clock that uses an electronic transition frequency in the microwave, optical, or ultraviolet region of the electromagnetic spectrum of atoms as a frequency standard for its timekeeping element...
s, thus only requiring the extraction of coarse timing information at the receiving end in order to achieve high-quality video synchronization. The extraction of coarse timing data is typically done using a phase locked loop with a long time constant.
Adequate bandwidth
Even with packet loss mitigation, video over IP will only work if the network is capable of carrying the content with some reasonable maximum packet loss rate. In practice, this means that video over IP will not work on overloaded networks. Since IP does not of itself offer any traffic guarantees, this must be applied at the network engineering level. One approach to this is the "quantity of service" approach which simply allocates sufficient bandwidth to video-carrying traffic that it will not congest under any possible load pattern. Other approaches include dynamic reduction in frame rate or resolution, network admission controlNetwork Admission Control
Network Admission Control refers to Cisco's version of Network Access Control, which restricts access to the network based on identity or security posture. When a network device is configured for NAC, it can force user or machine authentication prior to granting access to the network...
, bandwidth reservation, traffic shaping
Traffic shaping
Traffic shaping is the control of computer network traffic in order to optimize or guarantee performance, improve latency, and/or increase usable bandwidth for some kinds of packets by delaying other kinds of packets that meet certain criteria...
, and traffic prioritization techniques, which require more complex network engineering, but will work when the simple approach of building a non-blocking network is not possible. See RSVP
Resource Reservation Protocol
The Resource Reservation Protocol is a Transport Layer protocol designed to reserve resources across a network for an integrated services Internet. RSVP operates over an IPv4 or IPv6 Internet Layer and provides receiver-initiated setup of resource reservations for multicast or unicast data flows...
for one approach to IP network traffic engineering.
The Pro-MPEG Wide Area Network group has done much recent work on creating a draft standard for interoperable professional video over IP.
Use by Security Industry
Within the security products industry, IP-based Closed Circuit Television (CCTV) is making gains on the analog market. Key components of IP-based CCTV remain consistent with analog technologies: image captureImage Capture
Image Capture is an application program from Apple that enables users to upload pictures from digital cameras or scanners which are either connected directly to the computer or the network...
, with a combination of IP-based cameras or analog cameras using IP-based encoders; image transmission; Storage and Retrieval, which uses technologies such as RAID array
RAID
RAID is a storage technology that combines multiple disk drive components into a logical unit...
s and iSCSI
ISCSI
In computing, iSCSI , is an abbreviation of Internet Small Computer System Interface, an Internet Protocol -based storage networking standard for linking data storage facilities. By carrying SCSI commands over IP networks, iSCSI is used to facilitate data transfers over intranets and to manage...
for recorded and indexed video; and video management, which affords web browser-enabled management and control of IP-based CCTV systems.
One key advantage of IP-based CCTV is the ability to use network infastructure, providing adequate bandwidth and availability of switching and routing, rather than coaxial cabling. However, running bandwidth-intensive surveillance video over corporate data networks is a point of organizational contention, depending on the potential impact on network performance.
A class of companies produce Video Management Software to help manage capture and storage of video content. Digital video also makes possible Video Content Analysis, which allows automatic detection and identification of various kinds of objects or motion.
Also another emerging model is off-site storage of surveillance video. These online surveillance providers are utilizing cloud computing technologies to consolidate multi-site surveillance video over the web.
Manufacturers of CCTV equipment are steadily integrating IP network technology into their product portfolios.