Abstract:
A method for reporting a streaming quality is shown, wherein at least one continuous media stream is streamed to a client ( 601 ), and wherein said streaming is controlled by a protocol ( 109 ) that is operated between said client ( 601 ) and a server ( 600 ), the method including selecting at least one quality metric and a quality metrics class from a pre-defined set of at least two quality metrics classes, and reporting to said server ( 600 ) the quality of said streaming based on said at least one selected quality metric and said selected quality metrics class. The protocol ( 109 ) is preferably a Real-time Streaming Protocol in combination with a Session Description Protocol in the context of the 3GPP Packet-Switched Streaming Service. Also shown is a computer program, a computer program product, a system, a client, a server and a protocol.

Description:
FIELD OF THE INVENTION  
       [0001]     The invention relates to a method, a computer program, a computer program product, a system, a client, a server and a protocol for reporting a streaming quality in a streaming system, wherein at least one continuous media stream is streamed to a client, and wherein said streaming is controlled by a protocol that is operated between said client and a server.  
       BACKGROUND OF THE INVENTION  
       [0002]     Streaming refers to the ability of an application settled in a client to play synchronized media streams like audio and video streams in a continuous way while those streams are being transmitted to the client over a data network.  
         [0003]     Applications that can be built on top of streaming services can be classified into on-demand and live information delivery applications. Examples of the first category are music and news-on-demand applications. Live delivery of radio and television programs are examples of the second category.  
         [0004]     Streaming over fixed Internet Protocol (IP) networks is already a major application today. While the Internet Engineering Task Force (IETF) and the World Wide Web Consortium (W3C) have developed a set of protocols used in fixed-IP streaming services, no complete standardized streaming framework has yet been defined. For Third Generation (3G) mobile communications systems, according to the standards developed by the Third Generation Partnership Project (3GPP), the 3G Packet-switched Streaming Service (PSS, 3GPP TS 26.233) fills the gap between the 3G Multi-media Messaging Service (MMS), for instance downloading applications, and conversational services.  
         [0005]     The PSS enables mobile streaming applications, wherein the complexity of the terminals is lower than that required for conversational services, because no media input devices and encoders are required, and because less complex protocols can be used. The PSS includes a basic set of streaming control protocols, transport protocols, media codecs and scene description protocols.  
         [0006]      FIG. 1  schematically depicts the PSS protocol stack  1  that controls the transfer of both streamable and non-streamable content between a content or media server and a client.  
         [0007]     Streamable content  101 , such as video, audio and speech, is first converted to the payload format of the Real-time Transport Protocol (RTP)  102  in an adaptation layer  103 . Said RTP as defined by the IETF provides means for sending real-time or streaming data by using the services of an underlying User Datagram Protocol (UDP)  104 , which in turn uses the services of an underlying Internet Protocol (IP)  105 .  
         [0008]     Non-streamable content  106 , as for instance still images, bitmap and vector graphics, text, timed text and synthetic audio are transferred by the Hypertext Transfer Protocol (HTTP)  107 , which uses the services of the underlying Transport Control Protocol (TCP)  108  and the further underlying IP  105 .  
         [0009]     Whereas for the non-streamable content  106 , the built-in session set-up and control capabilities of the HTTP  107  are sufficient to transfer the content, in case of streamable content  101 , an advanced session set-up and control protocol has to be invoked, for instance to start, stop and pause a streaming video that is transferred from the content server to the client via the RTP/UDP/IP. This task is performed by the Real-time Streaming Protocol (RTSP)  109 , which may either use the underlying TCP  108  or the underlying UDP  104 . RTSP requires a presentation description  110  at least to set-up a streaming session. Such a presentation description  110  may for instance be available in the form of a Session Description Protocol (SDP) file. Said SDP file contains the description of the session, for instance session name and author, the type of media to be presented, information to receive said media, as for instance addresses, ports, formats and so on, and the bitrate of the media.  
         [0010]     If streaming content is to be viewed at the client side, for instance at a mobile terminal, the user of said terminal is first provided with a Universal Resource Identifier (URI) to specific content that suits his terminal. This URI may come form a WWW server, a Wireless Application Protocol (WAP) server, or may have been entered manually via the keyboard of the terminal. This URI specifies a streaming or RTSP server and the address of the content on that or another content server. The corresponding SDP file may now be obtained in a number of ways. It may be provided in a link inside the HTML page that the user downloads, for instance via an embed tag, or may also be directly obtained by typing it as a URI. The SDP file, i.e. the presentation description  110 , then is transferred via the HTTP  107  as indicated in the middle column of the protocol stack of  FIG. 1 .  
         [0011]     Alternatively, it may also be obtained through RTSP  109  signaling, for instance by using the DESCRIBE method of the RTSP  109 , as indicated by the right column of the protocol stack in  FIG. 1 . Note that the presentation description may equally well be transmitted by said RTP  102 . However, for simplicity of presentation, this possibility was not included in  FIG. 1 .  
         [0012]     The subsequent session establishment is the process in which the browser or the user of the mobile terminal invokes a streaming client to set up the session against the content server. The terminal is expected to have an active radio bearer that enables IP-based packet transmission at the start of session establishment signaling.  
         [0013]     The subsequent set-up of the streaming service is done by sending an RTSP SETUP message for each media stream chosen by the client. This returns the UDP  104  and/or TCP  108  port to be used for the respective media stream. The client sends an RTSP PLAY message to the content server that then starts to send one or more streams over the IP network.  
         [0014]     In order to offer service providers in PSS systems means to evaluate the end user streaming experience, streaming service quality metrics have been introduced in PSS systems, as presented in 3GPP Technical document (Tdoc) S4-030860: “Draft Rel-6 PSS Quality Metrics Permanent Document v.0.10”, which refers to 3GPP TSG-SA4 meeting #29 in Tampere, Finland, Nov. 24-28, 2003. The streaming client measures and feedbacks information on the quality of the actual streaming application to a streaming server, wherein said quality is defined in terms of said quality metrics. Said streaming server may for instance be an RTSP server, and said quality metrics may for instance be transported by using said RTSP and SDP.  
         [0015]     Because the service is transparent to the type of RAN and CN, only the streaming client and the streaming server are impacted by the PSS quality metrics. One consequence of this is that the measurements may not rely on information from protocol layers below the RTP layer (e.g. UDP, IP, PDCP, RLC).  
         [0016]     The terminal in a PSS system with quality feedback is responsible to perform the quality measurements in accordance to the measurement definition, aggregate them into streaming client quality metrics and report the metrics to the streaming server. This requirement does not preclude the possibility for the streaming client to report raw quality measurements to be processed by the streaming server into quality metrics.  
         [0017]     The streaming server is responsible to signal the activation of the streaming client&#39;s quality metrics reporting and to gather the streaming client&#39;s quality metrics. The streaming server may process the received streaming client&#39;s quality metrics to build aggregated quality metrics. E.g. it could receive a raw lost packets report and build the Min, Max, Avg and Std packet loss rate for a particular streaming client.  
         [0018]     The objective of the quality metric definition is to obtain consistent measurements across content type, terminals, and types of Radio Access Network (RAN).  
         [0019]     The constraints are to minimize the size of the quality metrics report that will be sent to the streaming server and, the complexity for the terminal.  
         [0020]     The quality metrics can be divided in 3 different types:  
         [0021]     A first set of metrics are computed from terminal-based media quality measurements (measured within the decoder or predicted at the decoder input), e.g. the corruption duration, which is defined as the time from the start of the first corrupted media (audio/speech/video) decoded frame to the start of the first subsequent decoded good frame or the end of the reporting period (whichever is sooner), not including the buffering freezes/gaps and pause freezes/gaps.  
         [0022]     A second set of metrics are computed by the terminal based on the general PSS protocol and the operation of the player that renders the streaming application. E.g. abnormal termination of a session.  
         [0023]     A third set of quality metrics are computed based on terminal-measured network characteristics. E. g. number of packets lost in succession.  
         [0024]     As already mentioned, in PSS systems RTSP is used for the feedback of quality reports according to the quality metrics.  FIG. 2   a  lists the definition of an RTSP protocol data unit header  2   a  QoE-Metrics for the negotiation of the quality metrics between the streaming client and the streaming server, and  FIG. 2   b  lists the definition of an RTSP protocol data unit header  2   b  QoE-Feedback for the actual feedback of quality metrics from the streaming client to the server, wherein QoE stands for “Quality of Experience”.  
         [0025]     The negotiation header  2   a  of  FIG. 2   a  can be used in two ways: 
    1. If only the Off parameter is used, this is an indication that either the streaming server or the streaming client wants to cancel the quality metrics monitoring and reporting.     2. If the header  2   a  contains other parameters, then the quality metrics transmission is requested to start (or restart in case of mid-session monitoring).    
 
         [0028]     If the negotiation header  2   a  is used with the RTSP Session Control url information, then QoE-Metrics is used at the session level. If the url is an RTSP Media Control url, then QoE-Metrics is used at the media level and each media gets its own QoE-Metrics line.  
         [0029]     It is required to set the sending rate. If the Sending-rate value is 0, then the streaming client can send feedback messages at any time depending on the events occurred in the streaming client. Values ≧1 indicate a precise message-sending interval. The shortest interval is once a second and the longest interval is undefined. The feedback sending interval can be different for different medium, but it is recommended to keep a sort of synchronization, to avoid extra traffic in the uplink direction. The value End indicates that only one message is sent at the end of the session. The Range field can be used to define the time limit of feedback sending. In this way it is possible to decide the monitoring time range during the negotiation phase.  
         [0030]     The actual quality metrics feedback can be conveyed to the PSS server by using the SET_PARAMETER method of the RTSP with the feedback header  2   b  of  FIG. 2   b.    
         [0031]     In the feedback header  2   b  of  FIG. 2   b , Stream-url is the RTSP session or media control URL identifier for the feedback parameter. The Metrics field in the Parameters definition contains the name of the metrics/measurements (for instance corruption duration, etc.) and it shall be the same as the Metrics field in the negotiation QoE header  2   a  (QoE-Metrics). It is recommended to keep the order of metrics the same to simplify parsing. The Value field indicates the results. There is the possibility that the same event occurs more than once during a monitoring period. In that case the metrics value can occur more than once, which indicates the number of events to the server. The optional Timestamp indicates the time when the event (or measurement) occurred or when the metric was calculated since the beginning of the session. Also no events can be reported (using the SP—space). The optional Range indicates the reporting period.  
         [0032]     Quality metrics reporting is normally done by the PSS client using the SET_PARAMETER method of the RTSP. However, in particular cases, it is more efficient to use other methods to carry the information, as for instance the TEARDOWN message or the PAUSE message.  
         [0033]     Turning back to the above-stated quality metrics definition of the corruption duration as a representative of a first set of quality metrics that are computed from terminal-based media quality measurements, it is readily seen that, apart from the dependency of this quality metrics definition on the further definition of a “corruption” and a “reporting period”, this quality metrics definition particularly depends on a definition of a “good frame”.  
         [0034]     A good frame is a media (audio/speech/video) decoded frame that is not corrupted, i.e. that doesn&#39;t contain any freezes/gaps or quality degradations. To declare a video or audio frame as good, in Tdoc S4-030860, the following definition is introduced: “A good frame is the earlier of N frames after last loss or a complete I-frame, where N is either (a) signaled or (b) defaults to ∞ (for video) or 1 (for audio)”.  
         [0035]     The application of this definition is not mandatory, resulting in a wide range of interpretations of the definition of a good frame. Thus different streaming clients may report different streaming qualities, because for the same quality metric (for instance corruption duration), different definitions for a “good frame” are applied. A similar ambiguity arises when different terminals use different error tracking algorithms, so that even when using the same definition of a “good frame”, the reported streaming quality in terms of the same quality metric may differ across the terminals. These ambiguities cause the reported quality metrics to be imprecise and effectively worthless.  
       SUMMARY OF THE INVENTION  
       [0036]     In view of the above-stated problems, it is, inter alia, an object of the present invention to provide a method, a computer program, a computer program product, a system, a client, a server and a protocol allowing for an improved, in particular a more significant reporting of a streaming quality.  
         [0037]     It is proposed a method for reporting a streaming quality, wherein at least one continuous media stream is streamed to a client, and wherein said streaming is controlled by a protocol that is operated between said client and a server, comprising selecting at least one quality metric and a quality metrics class from a pre-defined set of at least two quality metrics classes, and reporting to said server the quality of said streaming based on said at least one selected quality metric and said selected quality metrics class.  
         [0038]     Said at least one continuous media stream may for instance contain video, audio or speech information that is continuously transmitted from a server, for instance a content server, to said client and is rendered on the terminal, in which said client is set up, in a synchronized manner. This streaming may take place in a streaming session, wherein several media streams may be concurrently streamed to said client. Said streaming is controlled by said protocol, for instance a streaming protocol as the RTSP, and may for instance allow to start, stop and/or pause the streaming. Said RTSP is operated by protocol entities in said client and in said server and may be based on an SDP. Said server may be co-located or even be identical with the content server from which said continuous media actually stems from, or may be a different instance. The quality of said streaming is determined at the client site according to said at least one quality metric, as for instance a corruption duration or a re-buffering event. Said quality metrics class at least partially defines how said at least one quality metric has to be determined. For instance, if said at least one quality metric depends on the decision whether a frame of said continuous media stream is a good frame, said quality metrics class may define how this decision has to be come to. Said set of at least two quality metrics classes is pre-defined. In said step of selecting, at least said client or said server choose at least one quality metric, for instance from a pre-defined set of quality metrics, and at least said client or said server choose a quality metrics class from said pre-defined set of at least two quality metrics classes defined. Said pre-defined sets may for instance be defined within an RTSP and/or an SDP. Said step of selecting may further comprise the negotiation between said client and server on at least one of said quality metrics and a quality metrics class. Said negotiation may be done between said client and server through said protocol, for instance RTSP and SDP. Based on said at least one selected quality metric and said at said quality metrics class, said client then reports said quality of said streaming to said server.  
         [0039]     Thus according to a first aspect of the present invention, the incorporation of additional quality metrics classes restricts the interpretation of the quality metrics definitions and thus contributes to make the quality reports more significant and concise.  
         [0040]     According to a second aspect of the present invention, the incorporation of said additional quality metrics classes adds an additional degree of freedom in the definition of quality metrics. For instance, if a corruption duration, which, inter alia, depends on the decision whether frames of said continuous media stream are good frames or corrupted frames, is selected as quality metric, this quality metric can be further specialized by the selection of the quality metrics class, which may for instance provide a variety of definitions of a good frame. Thus, without loosing conciseness of the quality metric itself, because each definition of a good frame according to the quality metrics class is fixedly prescribed, the scope of application of the quality metric is extended.  
         [0041]     According to the method of the present invention, it may be preferred that said step of selecting said quality metrics class comprises the step of negotiating said quality metrics class between said client and said server. Said negotiation may be based on said protocol that also controls said streaming, for instance RTSP in combination with SDP, and may further comprise the negotiation of said at least one quality metric.  
         [0042]     According to the method of the present invention, it may be preferred that said protocol defines a quality metrics class field within at least one of its protocol data units, wherein said quality metrics class field is capable of identifying each quality metrics class of said pre-defined set of at least two quality metrics classes. Each quality metrics class may for instance be assigned a unique number, and said quality metrics class field then contains the number of the quality metrics class that has been selected. Similarly, said protocol data units may further contain a field for the identification of said at least one selected quality metric and a field for carrying a feedback value that has been determined according to said at least one quality metric and said quality metrics class. Said protocol data unit may either be a protocol data unit for negotiation or a protocol data unit for feedback. Signaling said selected quality metrics class during negotiation may be sufficient, so that no fields in feedback protocol data units may be required. Said field may be an optional field or mandatory field in said protocol data units.  
         [0043]     According to the method of the present invention, it may be preferred that said quality metrics class field is located in a header section of said at least one protocol data unit. Alternatively, it may also be comprises in the payload section of said at least one protocol data unit.  
         [0044]     According to the method of the present invention, it may be preferred that said at least one selected quality metric is a Quality of Experience (QoE) metric that is at least partially based on the decision whether at least one frame of said at least one continuous media stream is a good frame. Said quality metric may for instance be a corruption duration, wherein said corruption duration may be defined as the time between a corrupted frame and the next good frame.  
         [0045]     According to the method of the present invention, it may be preferred that each quality metrics class in said pre-defined set of at least two quality metrics classes defines a different set of rules on how to decide whether a frame of said continuous media stream is a good frame. Said quality metrics classes may for instance be based on an error tracking algorithm or on a decoding quality evaluation algorithm.  
         [0046]     According to the method of the present invention, it may be preferred that said set of rules defined by at least one of said quality metrics classes comprises deciding the earlier of a completely received I-frame of said at least one continuous media stream or the N-th completely received frame of said at least one continuous media stream after the last error or loss to be a good frame, wherein the integer N is either signaled or defaults to ∞ in case of a video frame or 1 in case of an audio frame, and deciding a frame of said at least one continuous media stream following a good frame to be a good frame, if said frame is completely received, and said frame and all subsequent frames until the next good frame to be corrupted, otherwise. Said I-frame may for instance be a frame within a coded video stream wherein said frame contains the complete pixel information. In case of the H.264 or MPEG-4 Advanced Video Coding (AVC) codecs, said I-frame represents an IDR-frame. If said client can derive the actually required value of N from extra information, e.g. information obtained from the AVC recovery point Supplemental Enhancement Information (SEI) message for AVC video, that value may override the signaled or default value of N. Said frame may be understood to be completely received if all bits encoding said frame are correctly received and no bit error occurred.  
         [0047]     According to the method of the present invention, it may be preferred that said set of rules defined by at least one of said quality metrics classes comprises deciding a coded frame of said at least one continuous media stream as a good frame based on an error tracking algorithm.  
         [0048]     According to the method of the present invention, it may be preferred that said set of rules defined by at least one of said quality metrics classes comprises deciding an intra-coded frame of said at least one continuous media stream to be a good frame, if it is completely received at said client, and to be a corrupted frame otherwise, or deciding a predictively coded frame of said at least one continuous media stream to be a good frame, if it is completely received at said client and if all its prediction reference samples belong to good frames, and to be a corrupted frame otherwise. Said intra-coded frames, for video, may be understood as frames without temporal motion-compensated prediction, but possibly with removal of spatial redundancy within the frame, and said predictively coded frames, for video, may be understood as frames with temporal motion-compensated prediction to reduce the temporal redundancy by taking advantage of the strong correlation among the video frames. Said prediction reference samples may for instance be prediction reference pixels in case of video.  
         [0049]     According to the method of the present invention, it may be preferred that said set of rules defined by at least one of said quality metrics classes comprises deciding a coded frame of said at least one continuous media as a good frame according to a decoding quality evaluation algorithm.  
         [0050]     According to the method of the present invention, it may be preferred that said set of rules defined by at least one of said quality metrics classes comprises deciding an intra-coded frame of said at least one continuous media stream to be a good frame, if it is completely received at said client, and to be a corrupted frame otherwise, or deciding a predictively coded frame of said at least one continuous media stream to be a good frame, if it is completely received at said client and all of its prediction reference samples belong to good frames, or if at least a part of said frame is completely received, all prediction reference samples, for instance reference pixels for video, of said completely received parts of said frame belong to good frames, and all concealed parts of said frame are considered as good, wherein concealed parts of said frame are obtained by applying an error concealment algorithm to lost or erroneous parts of a decoded version of said frame, and wherein said concealed parts are considered as good if an average boundary difference between said concealed parts and surrounding completely received and decoded parts of said frame is below a threshold. Said concealment may for instance comprise estimation of reconstruction of lost or erroneous pixels based on spatial and/or temporal neighbors of said pixels. Said average boundary difference may quantify a sum of luminance differences between pixels at the edges of concealed parts. Said threshold may for instance be equal to 3.  
         [0051]     According to the method of the present invention, it may be preferred that said protocol is a Real-time Streaming Protocol RTSP in combination with a Session Description Protocol SDP in the context of a Packet-Switched Streaming Service PSS of a third generation mobile communications system. Said SDP may for instance provide the presentation description that is required by the RTSP in order to control said streaming.  
         [0052]     According to the method of the present invention, it may be preferred that said SDP comprises at least one SDP attribute that defines at least one quality metrics class field, wherein said quality metrics class field is capable of identifying each quality metrics class of said pre-defined set of at least two quality metrics classes. Each quality metrics class may for instance be assigned a unique number, and said quality metrics class field then contains the number of the quality metrics class that has been selected. Similarly, said SDP attribute may further contain a field for the identification of said at least one selected quality metric.  
         [0053]     According to the method of the present invention, it may be preferred that said RTSP is used to negotiate a quality metrics class between said client and said server at least partially based on said SDP attribute. SDP may for instance be used to initiate the negotiation of quality metrics and quality metrics classes. It is then advantageous to add said field to the SDP attribute that is used for the negotiation initiation.  
         [0054]     According to the method of the present invention, it may be preferred that said RTSP uses a DESCRIBE method for said negotiation. Said negotiation may for instance be initiated by using said RTSP DESCRIBE method in conjunction with said SDP attribute.  
         [0055]     It is further proposed a computer program with instructions operable to cause a processor to perform the above-mentioned method steps. Said computer program may for instance be run on a processor that is integrated in either said client or said server.  
         [0056]     It is further proposed a computer program product comprising a computer program with instructions operable to cause a processor to perform the above-mentioned method steps.  
         [0057]     It is further proposed a streaming system, comprising at least one client, and at least one server, wherein at least one continuous media stream is streamed to said at least one client, and wherein said streaming is controlled by a protocol that is operated between said at least one client and said at least one server, wherein at least one quality metric and a quality metrics class from a pre-defined set of at least two quality metrics classes are selected, and wherein the quality of said streaming based on said at least one selected quality metric and said selected quality metrics class is reported to said at least one server.  
         [0058]     It is further proposed a client in a streaming system, comprising means for operating a protocol that controls a streaming of at least one continuous media stream to said client, means for selecting at least one quality metric and a quality metrics class from a pre-defined set of at least two quality metrics classes, and means for reporting the quality of said streaming based on said at least one selected quality metric and said selected quality metrics class to a server.  
         [0059]     It is further proposed a server in a streaming system, comprising means for operating a protocol that controls a streaming of at least one continuous media stream to a client, means for selecting at least one quality metric and a quality metrics class from a pre-defined set of at least two quality metrics classes, and means for receiving a reported quality of said streaming from said client, wherein said quality is reported based on said at least one selected quality metric and said selected quality metrics class.  
         [0060]     It is further proposed a protocol for a streaming system, comprising rules for the control of a streaming of at least one continuous media stream to a client, a definition of at least one quality metric and of a set of at least two quality metrics classes, rules for the selection of at least one quality metric and of a quality metrics class from said set of at least two quality metrics classes, and rules for the report of a quality of said streaming based on said at least one selected quality metric and said selected quality metrics class to a server. Said protocol may for instance be the RTSP in combination with the SDP in the context of a 3G PSS system.  
         [0061]     These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter. 
     
    
     BRIEF DESCRIPTION OF THE FIGURES  
       [0062]     In the figures show:  
         [0063]      FIG. 1 : A schematic representation of a Packet-Switched Streaming Service (PSS) protocol stack according to the prior art,  
         [0064]      FIG. 2   a : a definition of a Real-time Streaming Protocol (RTSP) negotiation header according to the prior art,  
         [0065]      FIG. 2   b : a definition of an RTSP feedback header according to the prior art,  
         [0066]      FIG. 3 : a definition of a modified RTSP negotiation header according to the present invention,  
         [0067]      FIG. 4 : an exemplary Macro Block (MB) status map for an error concealment algorithm according to the present invention,  
         [0068]      FIG. 5 : an illustration of a method for the calculation of an average boundary difference according to the present invention,  
         [0069]      FIG. 6 : a flowchart of the method of the present invention, and  
         [0070]      FIG. 7 : a schematic representation of a system according to the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0071]     For the present invention, the protocol stack of  FIG. 1  and the feedback RTSP header as defined in  FIG. 2   b  still apply. However, a modified negotiation RTSP header  3  is defined, as listed in  FIG. 3 .  
         [0072]     The modified negotiation RTSP header  3  of  FIG. 3  provides an additional RTSP field Metrics-class, which may either have the values “0”, “1” or “2”.  
         [0073]     During negotiation between the streaming client and the streaming server, thus not only the quality metric that is to be used in the subsequent quality feedback of the streaming client is agreed upon by utilizing the Metrics RTSP field of the modified negotiation RTSP header  3  of  FIG. 3 , but also the quality metrics class is negotiated by utilizing the Metrics-class RTSP field.  
         [0074]     If SDP is used to initiate QoE metrics negotiation, the Metrics-class field may also be added to the SDP attribute that is used for QoE negotiation initiation.  
         [0075]     The present invention proposes three different methods to judge whether frames of the continuous media stream that is streamed to the streaming client are good frames (otherwise they are considered as corrupted frames). Each of said respective methods is uniquely identified by one of the values “0”, “1” and “2” that the Metrics-class RTSP field can be assigned. Assuming that the quality metric is at least partially based on the decision whether frames are good or corrupted frames, for instance if the quality metric is a corruption duration, the overall information content of the quality metric obeying the judging method according to the selected quality metrics class is much more concise and significant.  
         [0076]     Furthermore, a specialization of the quality metric is achieved, because each quality metric at least partially based on good frame decision now is divided into three quality metrics, each with a different good frame judging method.  
         [0077]     In the sequel of this description, the three judging methods as proposed by the present invention will be discussed.  
         [0000]     First Judging Method  
         [0078]     The first method is similar as the one disclosed in Tdoc S4-030860, with some enhancing modifications. It is described as follows:  
         [0079]     A good frame is the earlier of 1) a completely received I-frame (for H.264 or MPEG-4 Advanced Video Coding (AVC) video, IDR-frame), or 2) the N-th completely received frame after the last error or loss, where N is either signaled or defaults to ∞ (for video) or 1 (for audio). If the client can derive the actually required value of N from extra information, e.g. information obtained from the AVC recovery point Supplemental Enhancement Information (SEI) message for AVC video, that value overrides the above-specified value. “Completely received” means that all the bits are received and no bit error occurred.  
         [0080]     If a frame following a good frame is completely received, it is a good frame. Otherwise, all subsequent frames from the frame in question (inclusive) to the next good frame (exclusive) are corrupted frames.  
         [0000]     Second Judging Method  
         [0081]     The second method is characterized by applying an error tracking algorithm. One possible embodiment of the second method is described as follows:  
         [0082]     For an intra-coded frame, if it is completely received, it is a good frame. Otherwise it is a corrupted frame.  
         [0083]     For a predictively coded frame, if it is completely received and all its prediction reference samples are belonging to good frames, it is a good frame. Otherwise it is a corrupted frame.  
         [0000]     Third Judging Method  
         [0084]     The third method is characterized by applying a certain decoding quality evaluation algorithm. A possible embodiment of the third judging method will be described in the sequel.  
         [0085]     The instance of the third method is at least partially based on the concealment of lost or erroneous parts of a predictively coded frame. Thus a parenthesis on the applied error concealment strategy of predictively coded frame has to precede the presentation of the instance of the third method.  
         [0086]     It is assumed that erroneous or incomplete parts of a frame are not decoded but discarded before decoding, therefore no integrity checking or bit-error detection is performed. All correctly received parts of a picture are decoded first, and then the lost parts are concealed. In practice, a record is kept in a macroblock (MB) based status map of the frame. The status of an MB in the status map is “Correctly received” whenever the part where the MB resides is available for decoding, and “Lost” otherwise. After the frame is decoded, if the status map contains “Lost” MBs, concealment is initiated.  
         [0087]     Given the structure of correctly received and lost parts of a frame and the MB-based status map of a frame, the applied concealment algorithm is MB-based. The missing frame area (pixels) covered by MBs marked as “Lost” in the status map are concealed MB-by-MB (16×16 Y pixels, 8×8 U, V pixels), wherein Y refers to luminance and U and V refer to chrominance pixels. After an MB has been concealed, it is marked in the status map as “Concealed”. Not only the “Correctly received” but also the “Concealed” MBs are treated as reliable neighbors in the concealment process whenever no “Correctly received” immediate neighbor of a “Lost” MB exists. In such cases, an unsuccessfully concealed MB can result in propagation of this concealment mistake to several neighboring concealed MBs. Therefore, the order in which “Lost” MBs are concealed is important. The processing starts with MB columns at the frame boundaries and then moves inwards column-by-column. This processing order helps to prevent a typical concealment mistake that is made in the usually “difficult” (discontinuous motion areas, large coded prediction error) center part of the frame from propagating to the “easy” (continuous motion area, similar motion over several frames) parts of the frame.  
         [0088]      FIG. 4  shows a snapshot of the status map during the concealment phase where already concealed MBs  402  have the status of “Concealed”, correctly received MBs  403  have the status of “Received”, lost MBs  400  have the status “Lost” and the currently processed (being concealed) MB  401  is marked as “Current MB”.  FIG. 4  further indicates a lost part  404 , that can only consist of concealed  402  or lost  400  MBs.  
         [0089]     Only “Correctly received” neighboring MBs  403  are used for concealment if at least two such MBs are available. Otherwise, neighboring “Concealed” MBs  402  are also used in the averaging operation.  
         [0090]     Instead of directly operating in the pixel domain a more efficient approach is to try to “guess” the motion in the missing pixel area (MB)  400  by some prediction schemes from available motion information of spatial or temporal neighbors. This “guessed” Motion Vector (MV) is then used for motion compensation using the reference frame.  
         [0091]     The copied pixel values give the final reconstructed pixel values for concealment, and no additional pixel domain operations are used.  
         [0092]     The motion activity of the correctly received parts (groups of correctly received MBs  403 ) of the current picture is investigated first. If the average MV is smaller than a pre-defined threshold (currently ¼ pixels for each MV component), all lost parts  404  are concealed by copying from the spatially corresponding positions in the reference frame. Otherwise, motion-compensated error concealment is used, and the MVs of the lost MBs  400  are predicted as described in the following paragraphs.  
         [0093]     The motion of a “Lost” MB  400  is predicted from a spatial neighbor MB&#39;s motion relying on the statistical observation, that motion of spatially neighboring frame areas is highly correlated. For example, in a frame area covered by a moving foreground scene object, the MV field is continuous, which means that it is easy to predict.  
         [0094]     The MV of a “Lost” MB  400  is predicted from one of the neighbor MBs (or 8×8 blocks). This approach assumes that the MV of one of the neighbor MBs (or blocks) models the motion in the current MB well. It was found in previous experiments, that median or averaging over all neighbors&#39; MVs did not give better results. For simplicity, in the current implementation the smallest neighbor block size that is considered separately as prediction is set to 8×8 Y pixels. The motion of any 8×8 block is calculated as the average of the motion of the spatially corresponding 4×4 or other shaped (e.g. 4×8) blocks.  
         [0095]     The decision of which neighbor&#39;s MV to use as prediction for the current MB  500  is made based on the smoothness of the concealed (reconstructed) and will be explained with reference to  FIG. 5 . During this trial procedure the concealment pixel values of MB  500  are calculated using the MV  501   a - d  of each candidate (motion compensated pixel values). The MV  501   a - d  that results in the smallest luminance change across block boundaries  502   a - d  when the block  500  is inserted into its place in the frame is selected. The zero MV case is always considered and this copy concealment (copy pixel values from the spatially corresponding MB in the reference frame) is evaluated similarly as other MV candidates.  
         [0096]     The winning prediction MV is the one which minimizes the side match distortion d sm , which is the sum of absolute Y pixel value differences of the IN-block  503  and neighboring OUT-block  504  pixels at the boundaries  502   a - d  of the current block  500 , as shown in eq. (1):  
                 min   ⁢           ⁢   arg       dir   ∈     {     top   ,   bot   ,   left   ,   right     }         ⁢     〈       d   sm     =       1   N     ⁢       ∑     j   =   1     N     ⁢                Y   ^     j   IN     ⁡     (     mv   dir     )       -     Y   j   OUT                  〉             (   1   )             
 
 where Ŷ j   IN  (mv dir ) is the j-th concealed Y value in the IN-blocks  503  using mv dir  to predict the MV, and Y j   OUT  is the j-th reconstructed Y value in the OUT-blocks  504 , and N is the total number of the calculated boundary pixels. 
 
         [0097]     When “Correctly received” neighbor MBs  403  exist, the side match distortion is calculated only over them. Otherwise, “Concealed” neighbor MBs  402  are included in the calculation.  
         [0098]     A possible embodiment of the third method now can be described as follows:  
         [0099]     For an intra-coded frame, if it is completely received, it is a good frame. Otherwise it is a corrupted frame.  
         [0100]     For a predictively coded frame: 
    a) If it is completely/correctly received and all its prediction reference samples are belonging to good frames, it is a good frame.     b) If at least part of the frame is completely/correctly received, and the prediction reference samples of completely/correctly received parts are belonging to good frames, the frame is judged using step c. Otherwise the frame is corrupted.     c) The frame is decoded and the lost or erroneous parts being concealed using the above-described error concealment algorithm. If the average boundary difference, i.e. the side match distortion of eq. (1), between a concealed part and the surrounded completely/correctly received and decoded part is smaller than a threshold, the concealed part is considered as good. If all the concealed parts are good, the frame is a good frame. Otherwise, the frame is corrupted.    
 
         [0104]     The threshold in this method may for instance be chosen equal to 3.  
         [0105]      FIG. 6  depicts a flowchart of the method for reporting a streaming quality according to the present invention. The method steps are represented by requests and acknowledgments that are exchanged between a streaming server  600  and a streaming client  601 , wherein said requests and acknowledgments obey the RTSP. Furthermore, it is readily seen that the method steps can be classified into a negotiation step  602  and a feedback step  603 .  
         [0106]     The Quality Metrics negotiation starts with a response  605  of the streaming server  600  to a DESCRIBE request  604  of the streaming client  601 . Into said response  605 , at least one quality metrics and a quality metrics class as desired by the streaming server  600  for the future quality reporting is embedded by means of Session Description Protocol (SDP) data. If the streaming client  601  supports quality metrics, then it shall send a SETUP request  606  containing the selected/modified quality metrics and quality metrics class for either session level, or the media level, which is being set-up.  
         [0107]     In order for the streaming client  601  to indicate that both session level and media level quality metrics are supported, the client may send all the supported/modified quality metrics related to the media level. It may also send the selected session level quality metrics in at least one of the SETUP requests. In the above SETUP request  606 , the client only modifies the sending rate of the quality metrics for the control URL as compared to the initial SDP description contained in the response  605  of the server  600 .  
         [0108]     Receiving this SETUP request  606 , the streaming server  600  returns back the 200/OK response  607  containing the accepted quality metrics and quality metrics class returned by the streaming client  601  (to re-acknowledge the changes). It may also reject the changes made by the streaming client  601 . If the streaming server  600  rejects the changes, it can either set new values and resend the modified quality metrics and quality metrics class back to the streaming client  601 , or it can simply ignore the quality metrics and quality metrics class and not re-acknowledge them.  
         [0109]     If the streaming server  600  does not approve the modifications done by the streaming client  601 , they can continue to re-negotiate until the RTSP PLAY request  608  and the RTSP PLAY response  609  of the streaming server  600  would return the final negotiated quality metrics and quality metrics class including all session and media level metrics values.  
         [0110]     The actual feedback according to the negotiated quality metric and quality metrics class then is performed in at least one step  610 , for instance based on the RTSP feedback header  2   b  as defined in  FIG. 2   b.    
         [0111]     It should be noted that each time the QoE-Metrics header field is sent in an RTSP request, it shall also be present in the response corresponding to that particular request. Otherwise, the receiver of the response assumes that the other end does NOT support Quality Metrics. The same may apply for the QoE-Metrics-Class header field.  
         [0112]      FIG. 7  schematically depicts the functional components of a system according to the present invention. The PSS system comprises a streaming client  601  and a streaming server  600 , wherein both client  601  and server  600  have at least one RTSP entity  701 ,  700  that is capable of operating the RTSP. The RTSP entities  700 ,  701  use the services of underlying protocol layers that are operated by further protocol entities, of which only the TCP/UDP entities  702 ,  703  and the IP entities  704 ,  705  are shown. The streaming client  601  is further connected to a streaming quality monitor instance  707 , which monitors the quality of the actual streaming application in terms of the negotiated quality metrics and quality metrics class and inputs monitored quality values into said RTSP entity  701 . Said streaming quality monitor may for instance be provided by the terminal, in which said streaming client is set up. Via the RTSP, said monitored quality values are transferred to the RTSP peer entity in the streaming server  600 , where they are input into a quality data processing instance  706  for evaluation and analysis, which may for instance aim at improving the quality of the streaming application by enhancing the data rate of the streaming application if it is found that the re-buffering events become too frequent.  
         [0113]     The invention has been described above by means of a preferred embodiment. It should be noted that there are alternative ways and variations which are obvious to a skilled person in the art and can be implemented without deviating from the scope and spirit of the appended claims. In particular, the quality metrics classes may be used to render the definition of any quality metric that is at least partially based on good frame decision more precisely and at the same time allow a specialization of said quality metric. For instance, quality metrics classes may provide different definitions of what is to be understood under a corruption itself, or may provide definitions for different degrees of frame corruptions, which then, in combination with a quality metric that at least partially depends on a definition of a corruption, allow for a much more concise reporting of streaming quality. The scope of the present invention is by no means restricted to application in third generation mobile communication system. Also application in different wireless and even wired streaming systems may be imagined.