1、 AMERICAN NATIONAL STANDARD FOR TELECOMMUNICATIONS ATIS-0100801.04.2005(R2015) Multimedia Communications Delay, Synchronization, and Frame Rate As a leading technology and solutions development organization, ATIS brings together the top global ICT companies to advance the industrys most-pressing bus
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8、e standards. The American National Standards Institute does not develop standards and will in no circumstances give an interpretation of any American National Standard. Moreover, no person shall have the right or authority to issue an interpretation of an American National Standard in the name of th
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10、nal Standards Institute require that action be taken periodically to reaffirm, revise, or withdraw this standard. Purchasers of American National Standards may receive current information on all standards by calling or writing the American National Standards Institute. Notice of Disclaimer b) Visual
11、 channel transmission time, also called video delay; c) Audio channel transmission time (or audio delay); d) Data channel transmission time or delay (and frame inter-arrival time); e) Temporal synchronization between channels. This standard specifies methods of measurement for these parameters in th
12、e applications described in 1.3. The standards scope is limited to cases where appropriate media input and output interfaces are present, or where these interfaces can be made available with optional test fixtures. The following applications are beyond the scope of this standard: a) Measuring aspect
13、s of system performance other than delay, synchronization, and frame rate. It is important to point out that delay, synchronization, and frame rate measurements do not completely characterize the quality of a multimedia transmission system. For example, the reproduction quality of Video Frames from
14、input to output is also of obvious importance to users. Subjective test methods employing representative users yield the best available assessment of video transmission quality. The optimization of such subjective performance for all quality parameters may take precedence over the optimization of th
15、e results of parametric measurements performed according to this standard. The bibliography lists several international recommendations on subjective assessment methods for entertainment and teleconference quality video transmission systems. It also lists standards for assessment of audio and data c
16、hannels. b) Unrestricted choice of useful and representative source content. The methods of measurement specified here require restrictions on their source signals for testing. Video source sequences with high motion activity often cause increased delay, decreased frame rate, and skewed audiovisual
17、synchronization in some multimedia applications. Therefore, measurements should use test scenes which are realistic for the application of the multimedia system under evaluation. Continuous audio tones or still video sequences will produce ambiguous delay measurements (but delay is of limited import
18、ance under these conditions). Other limitations are given in the sections for each measurement method. c) Measuring the performance aspects of systems where the input and output interfaces are not accessible. ATIS-0100801.04.2005 d) Limits for the parameters. This standard only provides methods to m
19、easure these parameters without providing values for evaluation. 1.2 Purpose The purpose of this standard is to ensure the uniform application of, provide a framework for, and provide definitions of performance parameters for transmission systems utilizing digital transport facilities, consistent wi
20、th the scope. This standard is intended to provide a common understanding among manufacturers, service providers, and their customers. 1.3 Application 1.3.1 User-to-User Channels Ideally, the delay measurement would be conducted at the user interfaces, so as to characterize the entire user-to-user d
21、elay. The complete user-to-user channel begins and ends with user interface devices. For example, consider the visual channel with its camera and display components, as shown in figure 1. Encoder DecoderVisual ChannelCameraDisplayInputOutputEncoder DecoderAudio ChannelEncoder DecoderData ChannelMicr
22、ophoneSource SinkSpeakerFigure 1 - User-to-User Channels in a Multimedia System Unfortunately, signals enter and leave this channel in the form of light, making the generation and collection of suitable signals for measurement a difficult task. To simplify the interconnection of measurement equipmen
23、t with the channel, the test channel between electrical interface connectors at the camera output and at the display input is specified. This has the advantage of providing more physical and logical structure to the test interface. The additional delay contributed by a camera and display could be as
24、sessed separately (these delays are expected to be constrained within the sample/display interval, may be constant for displays, and are usually test-signal independent) and added to the measurements of variable delay made in accordance with this standard. Similar input and output interfaces in audi
25、o user-to-user channels and data user-to-user channels can be identified. 1.3.2 Applicable Configurations The following channel configurations are appropriate applications of this standard. Each figure shows the necessary input and output interfaces. 2 ATIS-0100801.04.2005 Encoder DecoderInput Outpu
26、tDigital ChannelLocal Site Remote SiteFigure 2 - End-to-End Measurement EncoderDecoderInputOutput Digital ChannelsLocal SiteRemote SiteDigitalLoop-BackFigure 3 - Remote Digital Loop-Back Measurement EncoderDecoderInputOutput Digital ChannelLocal SiteFigure 4 - Local System Measurement These figures
27、show only an Encoder, Decoder, and Digital Channel for simplicity. The components that may comprise the media channel in these tests are not strictly limited, and further examples may be found in the definitions of the channels (clause 3). The results of measurements conducted in the configurations
28、of Figures 3 and 4 can be used to assess the delay of the digital channels by removing the delay attributable to the local system. Figure 5 shows a video channel measurement configuration with limited application. This would constitute a two-way delay measurement of two one-way systems and permit a
29、single measurement device. 3 ATIS-0100801.04.2005 EncoderDecoderInputOutput Digital ChannelsLocal SiteRemote SiteVideoLoop-BackDecoderEncoderFigure 5 - Remote Video Loop-Back Measurement The video loop-back is not appropriate for cases where the digital channels have asymmetrical delay. For video te
30、leconference systems encoding less than 30 frames per second, the coding of the forward path may influence the transmission delay of the return path, which would make loop-back testing inappropriate in this case. Under these circumstances, the two-way measurement would not reveal the desired one-way
31、 assessment. NOTE One-way assessment for symmetrical systems is simply one-half of the two-way delay. 1.3.3 Applicable interfaces Video The work leading to the development of this standard was primarily conducted using composite analog video signal interfaces (conforming, at least in spirit, with SM
32、PTE 170M). Many video transmission systems in use today, including video conference systems, have composite interfaces available. This is clearly a convenient interface for the measurements described in this standard. However, the design of video conference systems is rapidly changing from a collect
33、ion of components (using the composite interface) to more integrated systems. Furthermore, the demands of high quality video production exceed the capabilities of the composite analog signal. It will be necessary to apply this standard at new interfaces to keep pace with advancing technologies. Digi
34、tal component interfaces, computer monitor RGB interfaces, and digital camera interfaces are likely candidates. The measurement parameters defined here simply require the ability to supply Video Frames to the input and collect and compare Video Frames at the output of a visual channel. No technique
35、demands a composite interface, per se. To apply this standard at a general video input interface, equipment shall supply source frame pixel information according to the specific interfaces physical, logical, and timing conventions. At a general video output interface, equipment shall be able to sync
36、hronize collection with the output information structure and identify the Video Frame area (for analog composite active video area, see 5.3 of T1.801.03-2003 (R2008), for safe action area and safe title area, see SMPTE RP 27.3). To facilitate the measurements described in this standard on fully inte
37、grated systems, optional interface access features will be needed to support testing. The complexity of individual systems may not be appreciably increased if nearly all of the additional functions required to implement these interfaces are contained in the optional sub-system. These interface featu
38、res might be useful in other activities, such as fault isolation and manufacturing quality assurance, and should be desirable to manufacturers on this basis. 4 ATIS-0100801.04.2005 5 1.3.4 Applicable interfaces Audio This specification is applicable at all standardized audio interfaces. 1.3.5 Applic
39、able interfaces Data This specification is applicable at all standardized data interfaces. 2 NORMATIVE REFERENCES The following standards contain provisions which, through reference in this text, constitute provisions of this American National Standard. At the time of publication, the editions indic
40、ated were valid. All standards are subject to revision, and parties to agreements based on this American National Standard are encouraged to investigate the possibility of applying the most recent editions of the standards indicated below. T1.504a-1991, Packet-Switched Data Communication Service Per
41、formance Measurement Methods.1T1.517-1995, Digital Transport of Video Teleconferencing/Video Telephony Signals Video Test Scenes for Subjective and Objective Performance Assessment.1T1.801.02-1996, Digital Transport of Video Teleconferencing/Video Telephony Signals Performance Terms, Definitions, an
42、d Examples.1T1.801.03-1996, Digital Transport of One-Way Video Signals Parameters for Objective Performance Assessment 1ITU-T Recommendation BT.601-5, Encoding Parameters of Digital Television for Studios.2SMPTE RP 27.3-1989, Recommended Practice, Specifications for Safe Title Areas, Test Pattern fo
43、r Television Systems.3SMPTE 125M-1992, SMPTE Standard for Television Component Video Signal 4:2:2 Bit-Parallel Digital Interface.3SMPTE 259M-1993, SMPTE Standard for Television 10-Bit 4:2:2 Component and 4f NTSC Composite Signals Bit-Parallel Digital Interface.3SMPTE 170M-1994, SMPTE Standard for Te
44、levision Composite Analog Video Signal NTSC for Studio Applications.31This document is available from the Alliance for Telecommunications Industry Solutions (ATIS), 1200 G Street N.W., Suite 500, Washington, DC 20005. 2This document is available from the International Telecommunications Union. 3This
45、 document is available at . ATIS-0100801.04.2005 6 3 DEFINITIONS, ACRONYMS, and when the corresponding input sequence of frames possess distinguishable differences, then the current frame is categorized as a Repeated Frame. See note, 3.1.16. 3.1.18 Active Video Frame Identification: The process of c
46、omparing each output Video Frame with its preceding frame(s) in sequence and quantifying the extent of correspondence between each pair. When there is limited correspondence between a pair of frames (such that the differences measured are distinguishable from the measurement noise), and the correspo
47、nding input sequence of frames possess distinguishable differences, then the current frame is categorized as an Active Frame. See note, 3.16. 3.2 Acronyms V(q) and V(n) are matched, through the methods described in this specification; A(p) and A(m) are matched, through the methods described in this
48、specification. The time offset between associated audio and Video Frames at the input is (n)T(m)Tn)(m,oVAAV= This parameter indicates the position of the audio frame with respect to the Video Frame in time. The time offset between associated audio and Video Frames at the output is (q)T(p)Tq)(p,oVAAV
49、= Note that oAV(p,q) is the synchronization relationship perceived by a user at the channel output. The time skew between associated audio and Video Frames at the output, introduced by the transmission system channel, is n)(m,oq)(p,oq)(p,sAVAVAV= Following the convention of positive time delay, synchronization time lag is a positive value. If the second channel is leading, the parameter has a negative value. For systems operating at low frame rates, time skew other than zero may provide perceptually more-accurate lip-sync. For systems
