1、 International Telecommunication Union ITU-T J.242TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU (12/2006) SERIES J: CABLE NETWORKS AND TRANSMISSION OF TELEVISION, SOUND PROGRAMME AND OTHER MULTIMEDIA SIGNALS Measurement of the quality of service A method to reconstruct the received video sequence
2、seen at the receiver using transmission error information to monitor the perceptual video quality at the receiver in digital cable television and video telephony ITU-T Recommendation J.242 ITU-T Rec. J.242 (12/2006) i ITU-T Recommendation J.242 A method to reconstruct the received video sequence see
3、n at the receiver using transmission error information to monitor the perceptual video quality at the receiver in digital cable television and video telephony Summary ITU-T Recommendation J.242 specifies a method for a transmitting side to reconstruct the received video sequence seen at a receiver u
4、sing transmission error information. The method can be used with an objective model for video quality measurement to monitor the quality of the received sequence. It is suggested that a standardized method should be used. The method in this Recommendation is applicable in order to: monitor the video
5、 quality of the received sequence seen at the receiver, with a minimum consumption of additional bandwidth; assess the real-time video quality of the received video sequence by the transmitting side. Source ITU-T Recommendation J.242 was approved on 14 December 2006 by ITU-T Study Group 9 (2005-2008
6、) under the ITU-T Recommendation A.8 procedure. ii ITU-T Rec. J.242 (12/2006) FOREWORD The International Telecommunication Union (ITU) is the United Nations specialized agency in the field of telecommunications. The ITU Telecommunication Standardization Sector (ITU-T) is a permanent organ of ITU. IT
7、U-T is responsible for studying technical, operating and tariff questions and issuing Recommendations on them with a view to standardizing telecommunications on a worldwide basis. The World Telecommunication Standardization Assembly (WTSA), which meets every four years, establishes the topics for st
8、udy by the ITU-T study groups which, in turn, produce Recommendations on these topics. The approval of ITU-T Recommendations is covered by the procedure laid down in WTSA Resolution 1. In some areas of information technology which fall within ITU-Ts purview, the necessary standards are prepared on a
9、 collaborative basis with ISO and IEC. NOTE In this Recommendation, the expression “Administration“ is used for conciseness to indicate both a telecommunication administration and a recognized operating agency. Compliance with this Recommendation is voluntary. However, the Recommendation may contain
10、 certain mandatory provisions (to ensure e.g. interoperability or applicability) and compliance with the Recommendation is achieved when all of these mandatory provisions are met. The words “shall“ or some other obligatory language such as “must“ and the negative equivalents are used to express requ
11、irements. The use of such words does not suggest that compliance with the Recommendation is required of any party. INTELLECTUAL PROPERTY RIGHTS ITU draws attention to the possibility that the practice or implementation of this Recommendation may involve the use of a claimed Intellectual Property Rig
12、ht. ITU takes no position concerning the evidence, validity or applicability of claimed Intellectual Property Rights, whether asserted by ITU members or others outside of the Recommendation development process. As of the date of approval of this Recommendation, ITU had received notice of intellectua
13、l property, protected by patents, which may be required to implement this Recommendation. However, implementers are cautioned that this may not represent the latest information and are therefore strongly urged to consult the TSB patent database at http:/www.itu.int/ITU-T/ipr/. ITU 2007 All rights re
14、served. No part of this publication may be reproduced, by any means whatsoever, without the prior written permission of ITU. ITU-T Rec. J.242 (12/2006) iii CONTENTS Page 1 Scope 1 2 References. 1 3 The Method. 1 3.1 Applications 3 4 Messages for sending transmission error information 4 4.1 Messages
15、for decoder information (receiver model information) 4 4.2 Source identifier . 4 4.3 Messages for lost packets . 4 4.4 Messages for delayed frames 4 4.5 Messages for skipped frames 4 4.6 Hand shaking and error handling . 4 4.7 Messages for additional information for transmission errors. 5 Appendix I
16、 Example of error message formats 6 I.1 Messages for decoder information (receiver model information) 6 I.2 Source identifier . 6 I.3 Messages for lost packets . 6 I.4 Messages for delayed frames 6 I.5 Messages for skipped frames 7 iv ITU-T Rec. J.242 (12/2006) Introduction Objective video quality m
17、easurement methods may be classified into three categories: full-reference (FR) models, reduced-reference (RR) models, and no-reference (NR) models. Generally, the accuracy of no-reference models is inferior to that of the FR and RR models. However, both FR and RR models require transmission of addi
18、tional data for video quality assessment. Since bandwidth is a valuable resource in multimedia applications, it is desirable to avoid the transmission of additional data. In a typical multimedia application, video data is transmitted using packets. During transmission, various errors might occur, wh
19、ich include packet loss and delay. These errors can produce frame freezing, frame skipping, block errors, jittering, delay, etc. In packetized video transmission, all these transmission errors and their effects can be accurately identified. Furthermore, in digital communications, if there are no tra
20、nsmission errors, the video quality of the received sequence will be identical to that of the transmitted sequence. ITU-T Rec. J.242 (12/2006) 1 ITU-T Recommendation J.242 A method to reconstruct the received video sequence seen at the receiver using transmission error information to monitor the per
21、ceptual video quality at the receiver in digital cable television and video telephony 1 Scope This Recommendation specifies a method for a transmitting side to reconstruct the received video sequence in order to monitor video quality at the receiver using transmission error information for packetize
22、d video transmission. This Recommendation applies to video services where two-way digital communications are available. The method in this Recommendation requires that each packet can be traced and identified. Some packet transport protocols such as RTP (real-time transport protocol) and ATM (asynch
23、ronous transfer mode)/AAL (ATM adaptation layer) have this feature. In order to evaluate video quality at the receiver, the method needs to be used with objective models for video quality measurement such as those contained in ITU-T J.144. It is suggested that a standardized method should be used. 2
24、 References The following ITU-T Recommendations and other references contain provisions which, through reference in this text, constitute provisions of this Recommendation. At the time of publication, the editions indicated were valid. All Recommendations and other references are subject to revision
25、; users of this Recommendation are therefore encouraged to investigate the possibility of applying the most recent edition of the Recommendations and other references listed below. A list of the currently valid ITU-T Recommendations is regularly published. The reference to a document within this Rec
26、ommendation does not give it, as a stand-alone document, the status of a Recommendation. ITU-T J.144 ITU-T Recommendation J.144 (2004), Objective perceptual video quality measurement techniques for digital cable television in the presence of a full reference. ITU-R BT.1683 ITU-R Recommendation BT.16
27、83 (2004), Objective perceptual video quality measurement techniques for standard definition digital broadcast television in the presence of a full reference. 3 The Method Figure 1 illustrates the procedure. The transmitting side includes a transmitter, a received video estimation unit and a video q
28、uality estimation unit, and may also include an encoder. According to this method, the quality of the received video sequence seen at the receiver can be evaluated at the transmitting side. Therefore, the source video sequence, or features extracted from the source video sequence, must be available
29、to the transmitting side. 2 ITU-T Rec. J.242 (12/2006) J.242(06)_F01Transmitting sideReceiverEncoder Transmitter DecoderReceivedvideosequencePacketizedvideo dataSourcevideosequenceReceived videoestimation unitEstimated receivedvideo sequenceVideo qualityevaluation unitTransmission errordetection uni
30、tFigure 1 A method for a transmitting side to monitor video quality at a receiver using transmission error information The transmitting side transmits packetized video data to the receiver. It is noted that packetization is applied to compressed video data. The receiver has a transmission error dete
31、ction unit which detects the occurrence of transmission errors. If transmission errors occur, the transmission error detection unit sends the transmission error information, which includes packet loss and delay, along with their effects such as frame freezing, frame skipping, block errors, jitter, e
32、tc. to the transmitting side (Table 1 shows typical transmission error information). Then, the received video estimation unit in the transmitting side emulates the receiver and estimates the received video sequence seen at the receiver using the transmission error information and the packetized vide
33、o data produced by the encoder. Finally, a video quality evaluation unit computes the video quality scores at the receiver using the source video sequence and the estimated received video sequence. Figure 2 shows an example of the method when a FR model is used. The estimated received video sequence
34、 in Figure 3 is produced by the received video estimation unit (Figure 2). When the source video sequences are not available at the transmitting side, it is also possible for the transmitting side to use an RR model, provided that feature parameters are available. J.242(06)_F02Transmitting sideRecei
35、verTransmitterReceivedvideosequenceSourcevideosequenceEstimatedreceived videosequenceChannelFRmodelFigure 2 A block diagram for the transmitting side computing the video quality of the received video sequence using the estimated received video sequence (FR model) ITU-T Rec. J.242 (12/2006) 3 J.242(0
36、6)_F03Video telephone terminalTransmission errordetection unitDecoderEncoder TransmitterPacketizedvideo dataReceivedvideosequenceSourcevideosequenceReceived videoestimation unitEstimated receivedvideo sequenceVideo qualityevaluation unitTransmission errordetection unitDecoderTransmitter EncoderRecei
37、vedvideosequenceSourcevideosequenceReceived videoestimation unitVideo qualityevaluation unitVideo telephone terminalTelecommunicationcompanyTransmission error informationPacketizedvideo dataEstimated receivedvideo sequenceTransmission error informationFigure 3 A method for a transmitting side to mon
38、itor video quality at a receiver using transmission error information (video telephony) A video telephone terminal both transmits and receives video signals. Provided that packetized video transmission or similar transmission methods are used, the method can be used in video telephones. Figure 3 ill
39、ustrates how the method can be used for video telephony. In packetized video transmission, the effects of transmission errors can be described as follows: Video degradation, such as block errors due to packet loss. Skipped (lost) frames due to packet loss, delay, overflow and underflow. Delayed fram
40、es due to packet delay and underflow. Therefore, if the receiver sends information on lost or impaired packets, skipped frames and delayed frames to the transmitting side, the transmitting side can reconstruct the received video sequences seen at the receiver. On the other hand, in video telephony (
41、Figure 3), the telecommunication company may want to monitor video quality at the receiver. In this scenario, the telecommunication company may use an NR objective video quality measurement method which uses bit stream data. In this case, the performance of such an NR method can be improved if the r
42、eceiver sends additional information on transmission errors, which includes information on BER (bit error rate), delayed packets, etc. Similarly, some service providers (transmitting side) are provided with compressed video data and may not have any information on source video sequences. In this cas
43、e, an NR method which uses bit stream data may be used and the receiver may send the additional information on transmission errors. 3.1 Applications The method can be used for packetized video transmission when two-way digital communications are available. The method further requires that each packe
44、t can be traced and identified. Some packet transport protocols such as RTP (real-time transport protocol) and ATM (asynchronous transfer mode)/AAL (ATM adaptation layer) have this feature. For example, the method can be used for VoD, IPTV, video telephony and videoconferencing. 4 ITU-T Rec. J.242 (
45、12/2006) 4 Messages for sending transmission error information In this method, the transmitting side and the receiver are cooperative since the receiver provides all the necessary information to the transmitting side. It is also noted that all information on the decoder and post-processing technique
46、s used in the receiver must be provided so that the transmitting side can exactly estimate the video sequence at the receiver. In order for the transmitting side to estimate the received video sequences, the required transmission error information is summarized in Table 1. For each transmission erro
47、r, an error-type specific message is transmitted. Such messages consist of two or three fields: type and binary numbers. A number of messages can be combined and then transmitted. Table 1 Transmission error information Type of transmission error Contents of transmission information Lost or impaired
48、packets Corresponding packet indexes Delayed frames Length of the delay and delayed frame indexes Skipped or lost frames Skipped or lost frame indexes 4.1 Messages for decoder information (receiver model information) In order to exactly estimate the received video sequence, the transmitting side nee
49、ds information on the decoder and post-processing techniques used at the receiver. For this purpose, at the beginning of transmission, the receiver needs to transmit a model identification message. It is assumed that the transmitting side has access to a database and can obtain all the necessary information on the decoder and post-processing techniques of the receiver from the model identification message. 4.2 Source identifier In broadcasting and multicasting environments, when the transmitting side receives transmission error messages, it needs to identify the
