When a compression-coding method such as MPEG-2 standard (ISO/IEC 13818) or H.246 is used in video distribution such as digital broadcasting using radio waves or video distribution such as digital broadcasting using a communication network, an original video image is compression-coded to frames (pictures) such as I, P, and B frames to generate an elementary stream, and the elementary stream is divided into packets called TS packets (Transport Stream Packets) and distributed.
If due consideration must be given to copyright in such video distribution, the payload portion of a TS packet where video data or audio data is stored is encrypted. The encrypted TS packet is received and decrypted by a reception terminal, and finally output as a video and supplied to a viewer.
In these video applications, if an atmospheric condition deteriorates in video distribution using radio waves, or packet loss or delay occurs in a network or a terminal for video distribution using a network, the video quality degrades, resulting in poor service quality. To provide a stable service, it is necessary to manage the quality of a communication network or a terminal to ensure predetermined video quality.
Such quality control requires to manage the quality state by measuring the influence of an atmospheric condition or network quality (e.g., packet loss or delay) on the quality of a video viewed by a user.
A video signal compressed by efficient encoding is transmitted using motion prediction encoding between frames. Since pieces of frame information on the preceding and succeeding sides are used, an atmospheric condition or TS packet loss in a network or a terminal, which causes loss of a packet, may degrade the video quality not only in one video frame but throughout a plurality of frames.
In this case, the video quality degrades in the decoded video of a succeeding frame even without packet loss. The atmospheric condition or packet loss on the network does not necessarily correspond to degradation in the video application. Hence, to accurately obtain the correspondence relationship between the atmospheric condition or network quality and the application quality, it is necessary to correctly grasp the range of influence of quality degradation based on encoded information.
To grasp the range of influence of quality degradation based on encoded information, a technique has been proposed, in which each packet is added with frame type information and distributed, and the receiving side acquires the frame type information and calculates the number of frames to be affected by degradation based on a degraded frame type and the states of preceding and succeeding frames (e.g., Japanese Patent Laid-Open No. 2006-33722). This technique is poor in versatility because frame type information needs to be added to each packet.
To grasp the range of influence of quality degradation based on encoded information, another technique has conventionally been proposed, which calculates the number of frames to be affected by degradation based on a degraded frame type and the states of preceding and succeeding frames (e.g., Japanese Patent Laid-Open No. 2007-60475).