Patent Publication Number: US-2005141850-A1

Title: Method and apparatus for displaying a received stream of audiovisual information

Description:
The invention relates to a method of displaying a received stream of audiovisual information which is interrupted at a point of interruption during display and in which the display of the stream of audiovisual information is resumed from the point of interruption after the end of the interruption.  
      An embodiment of such a method is known from WO 01/22729 A1. WO 01/22729 A1discloses a method of displaying a stream of audiovisual information. The display of the stream of audiovisual information can be interrupted by interactive applications such as a menu. In such a case, a point of interruption at which the stream of audiovisual information is interrupted is stored. After the interactive application, the stream of audiovisual information is displayed from the point of interruption.  
      The method described in WO 01/22729 A1 has the drawback that the display of the program material trails the transmission of the program material, with a unit of time which is equal to the duration of the interaction.  
      The invention also relates to an apparatus adapted to receive a stream of audiovisual information and to display this stream on a display device, the apparatus being further adapted to interrupt the display at a point of interruption during the display of the stream of audiovisual information, and to a resume the display of the stream of audiovisual information from the point of interruption after the end of the interruption.  
      It is an object of the invention to mitigate the drawbacks of the prior art.  
      This object is achieved with a method according to the invention, which is characterized in that, after resuming the display of the stream of audiovisual information, the stream of audiovisual information is displayed at an accelerated rate up to the point where the displayed stream of audiovisual information is synchronous with the received stream of audiovisual information, further referred to as point of synchronization.  
      This method has the advantage that, if the program expects the viewer to perform a quick interaction with respect to the transmission of the stream of audiovisual information, there is no backlog after the point of synchronization in the display of the audiovisual information and enables a user to react as fast as possible to events in the stream of audiovisual information.  
      An embodiment of the method according to the invention, in which the stream of audiovisual information is built up of consecutive frames, is characterized in that the accelerated display is effected by displaying key frames only, which are chosen on the basis of the information density in the stream of audiovisual information in the vicinity of the key frames.  
      This embodiment has the advantage that the segments of the stream of audiovisual information comprising much information can be displayed in a more extensive way to the user than segments of the stream of audiovisual information comprising relatively less information.  
      The apparatus according to the invention is characterized in that, after resuming the display of the stream of audiovisual information, the apparatus is further adapted to display the stream of audiovisual information at an accelerated rate up to the point where the display of the stream of audiovisual information is synchronous with the reception of the stream of audiovisual information, further referred to as point of synchronization. 
    
    
      These and other aspects of the invention are apparent from and will be elucidated with reference to the embodiments described hereinafter.  
      In the drawings:  
       FIG. 1  shows an embodiment of the apparatus according to the invention,  
       FIG. 2  is an illustration to support the explanation of an embodiment of the method according to the invention. 
    
    
       FIG. 1  shows a system  100  as an embodiment of the invention. The system  100  is adapted to receive and display audiovisual information. The system  100  is also adapted to receive application data comprising instructions which can be performed by a processing unit and to perform said applications. The applications may be interactive applications. The system  100  comprises an apparatus  110 , a display device  102  and an operating panel  104 .  
      The apparatus  110  comprises a processing unit  111 , a first memory  112 , a receiver  113  and a second memory  114 . This apparatus may be a set top box but also another type of dedicated apparatus for passing on and/or displaying audiovisual information. In a further embodiment of the invention, the apparatus  110  is personal computer. This does not depart from the scope of the invention.  
      The receiver  113  is adapted to receive an input signal  115 . The input signal  115  comprises at least a stream of audiovisual information. In a further embodiment, the input signal  115  comprises a stream of audiovisual information as well as a data stream in accordance with the MHP standard in order that applications in the form of instructions which can be executed by the processing unit  111  can also be transmitted. In a further embodiment of the invention, the input signal  115  is a high-frequency signal on which at least a stream of audiovisual information is superimposed.  
      In a preferred embodiment, the input signal  115  is a signal in accordance with the DVB standard. In a further embodiment, the input signal  115  may be, for example, a data stream in accordance with the TCP/IP standard.  
      If the input signal  115  is a high-frequency signal on which the stream of audiovisual information is superimposed, the receiver  113  is also adapted to demodulate the input signal  115  and extract the stream of audiovisual information from the input signal  115 .  
      In a further embodiment, the receiver  113  is a tuner which is known per se. If the input signal  115  comprises a stream of audiovisual information as well as a data stream, the receiver  113  is also adapted to separate the data stream and the stream of audiovisual information.  
      In the embodiment shown, the receiver  113  passes on the stream of audiovisual information and the data stream to the processing unit  111 . The processing unit  111  is adapted to pass on the stream of audiovisual information to the display device  102  for displaying the audiovisual information. The processing unit  111  in the embodiment shown is also adapted to store the stream of audiovisual information in the first memory  112 . In the presented embodiment of the invention, the first memory  112  is a hard disk drive system. However, those skilled in the art will understand that the first memory may be an opto-magnetic disc, a solid-state memory such as a flash memory or another mass storage device. The processing unit is also adapted to read a stream of audiovisual information stored in the first memory  112  and pass it on to the display device  102  in such a way that it can be displayed on the display device  102 . This enables a user to check different aspects of the display by means of the operating panel  104 . Said aspects may be, for example, trick play modes such as fast forward, rewind or pause. This is known per se.  
      In the presented embodiment, said data stream is also stored in the first memory  112 .  
      The processing unit  111  is further adapted to perform applications comprised in said data stream. Associated images and sounds may be displayed on the display device  102 . If interactive applications are concerned, the user of the system  100  may give entries to the apparatus  110  by means of the operating panel  104 . If the user enters information which is used in an application at a later stage, this information is stored in the second memory  114  in this embodiment, which second memory is preferably a rapidly accessible memory such as a SRAM or DRAM.  
      As mentioned hereinbefore, a stream of audiovisual information and a data stream comprising instructions which can be performed by a processing unit for the relevant applications is also transmitted together with the input signal  115 . In this embodiment of the invention, the stream of audiovisual information is interrupted by applications. These applications may start themselves at a given instant but the start of the applications may also be triggered by information in the stream of audiovisual information. In a further embodiment, the display device  102  shows a message to start an application if the user does not give a signal to the apparatus  110  within a predetermined time limit that the application should not be performed. This is effected by means of the operating panel  104 . In the preferred embodiment of the invention, these applications are sent along with the audiovisual information in accordance with the MHP standard, and controlled in the DVB format in the preferred embodiment.  
      If a stream of audiovisual information is interrupted by an application, the user misses a part of the stream of audiovisual information. By storing the stream of audiovisual information in the first memory  112 , reading of the stream of audiovisual information and its display on the display device  102  can be stopped if the application is started. Reading and displaying the stream of audiovisual information is subsequently resumed when the application has been ended.  
      However, if the stream of audiovisual information is not available in the first memory  112  but is directly passed on by the processing unit  111  from the receiver  113  to the display device  102 , this possibility does not exist. A solution to this problem is now presented with reference to  FIG. 2 .  FIG. 2  shows a received stream of audiovisual information  200 , a displayed stream of audiovisual information  210 , an application  220  and a time scale  250 .  
      In the presented embodiment of the invention, said problem is solved by storing the received stream of audiovisual information  200  in the first memory  112  as from the interruption of the display of the displayed stream of audiovisual information  210  by the application at the first instant  252 . After the end of the application at a second instant  253 , the display of the stream of audiovisual information  210  is resumed. A part of the received stream of audiovisual information  200  stored from the first instant  252  is displayed on the display device  102 . According to the invention, a stored part of the stream of audiovisual information  202  is displayed at an accelerated rate after the second instant  253  until the displayed stream of audiovisual information  210  is synchronous again with the received stream of audiovisual information  200 . The point at which the displayed stream of audiovisual information  210  and the received stream of audiovisual information  200  are synchronous with each other is shown as a point of synchronization  254  in  FIG. 2 .  
      In a preferred embodiment of the invention, the duration of a synchronization period  260  is fixed. The ratio between the time required for playing the stored part  202  in the standard play mode and the predetermined synchronization period defines the playback speed of the stored part  202  in the synchronization period  260 . In a further embodiment of the invention, only the ratio between the time taken for playing the stored part  202  in the standard play mode and the synchronization period is determined in advance. In this way, the synchronization period  260  is determined. A further embodiment enables the user to determine the synchronization period of his own preference.  
      In a preferred embodiment of the invention, the synchronization process proceeds automatically after the end of the interruption. This means that, after the end of the application, the accelerated display of the stored stream of audiovisual information  202  up to the point of synchronization  254  is started automatically. In a further embodiment of the invention, this is not effected automatically and the user is enabled to synchronize; by means of a button on the operating panel  104 , the displayed stream of audiovisual information with the received stream of audiovisual information.  
      In a preferred embodiment of the invention, the stored part  202  is displayed on the display device  102  at a constant speed during the synchronization period  260 . In a further embodiment of the invention, the display speed of the stored part  202  is determined by the information density of portions of the stored part. If a segment of the stored part  202  comprises much information, it is displayed at a slower speed than a segment of the stored part  202  comprising little information. For example, a dialogue between two people comprises much information and an impression of a landscape taking 5 minutes generally comprises little information. Based on the information in the stored part  202 , the processing unit  111  subsequently defines a number of key frames which are displayed during the synchronization process. A relatively large number of key frames is chosen from a segment comprising much information and a relatively small number of key frames is chosen from a segment with little information. During the synchronization process, only the key frames are subsequently displayed.  
      In a further embodiment, the key frames are allocated in advance or during transmission by a content provider. In yet another embodiment, the stored part  202  consists of key frames only. This has the advantage that less space is required in the first memory  112 .  
      In the described embodiments of the invention, the stored part  202  is locally stored in apparatus  110  in the first memory  112 . However, it is also possible to store the stored part  202  in a third memory (not shown) with the content provider. During the synchronization period  260 , only the key frames are presented via the input signal  115  to the system  100  for the purpose of display on display device  102 .  
      An application in accordance with the MHP standard has been mentioned as an interruption in relation to the displayed embodiment of the invention. It will be evident to those skilled in the art that this may be alternatively a different application. In a further embodiment of the invention, the input signal is a standard analog high-frequency signal in accordance with the PAL or NTSC standard and the data comprising instructions which can be performed by a processing unit on applications is already available in the second memory  114  as from the manufacture of the apparatus  110 , which second memory has a non-volatile character in this embodiment such as a battery-backed SRAM or an EEPROM memory. It is also possible that the interruption is generated by the user giving the apparatus  110  a command via the operating panel  104 .  
      In summary, the invention relates to a method and apparatus ( 110 ) for receiving and displaying a stream of audiovisual information ( 200 ). During display of the stream of audiovisual information ( 200 ), the display may be interrupted by an application ( 220 ). This causes a user to miss part of the audiovisual information ( 200 ). It is therefore proposed to store the audiovisual information ( 200 ) during the application ( 220 ) and present the missed content ( 202 ) to the user after the interruption. The storage is automatically triggered by the start of the application ( 220 ). However, this causes a delay in the display of the audiovisual information ( 200 ). The user is offered the possibility to let the displayed stream of audiovisual information ( 210 ) catch up with the received audiovisual information ( 200 ). This catch-up may be performed automatically, triggered by the end of the application ( 220 ).