Abstract:
The invention relates to the field of describing multimedia scenes. A data stream in the BIFS format 121 comprises, in conventional manner, two types of data, descriptions of the scenes 122 and commands 123. According to the invention, a data-processing device intended to convert data from a first format, for example, the BIFS text format, into a second format, for example, the BIFS binary format, comprises a scene transcoder 101 intended to convert the descriptions of the scenes 122 from the first format into the second format, and a command transcoder 111 intended to convert the commands 123 from the first format into the second format and having access to information comprised in the scene description. The invention is particularly interesting for conceiving descriptions of multimedia scenes using, for example, the MPEG4 standard.

Description:
FIELD OF THE INVENTION  
         [0001]    The invention relates to a data-processing device for converting data from a first format into a second format, said data comprising at least a scene description and a command intended to modify said scene description.  
           [0002]    The invention also relates to a data-processing method of converting data from a first format into a second format, said data comprising at least a scene description and a command intended to modify said scene description.  
           [0003]    The invention also relates to a program comprising program code instructions for performing the steps of this method when said program is executed on a processor.  
           [0004]    The invention is used in, for example, a system intended to conceive audiovisual data in an MPEG format.  
         BACKGROUND OF THE INVENTION  
         [0005]    The MPEG4 standard is notably described in the document ISO/IEC 14496-1, entitled “Information Technology—Very Low Bit Rate Audiovisual Coding—part 1: Systems” published by ISO in 1999. This standard particularly describes a binary scene format BIFS having for its object to describe spatiotemporal relations between various graphic objects of a scene. Information which is necessary for composing a scene constitutes a scene description. A concept of a scene description is given in section 9 of this standard. A scene description has a tree structure composed of nodes, each node corresponding to an object and comprising a set of fields. Routes are used to assign the value of one field to another field. A data stream in BIFS format comprises two types of data, scene descriptions and commands. The commands may be of two types:  
           [0006]    commands for replacing the scene, comprising a whole scene description,  
           [0007]    commands for modifying the scene, comprising modifications to be applied to a scene description, like a replacement of one node by another, an addition or a suppression of a node, a modification of a field or of a route.  
           [0008]    A scene description is generally written by an author by using a user-friendly format, for example, a text format. The commands are generally written in the same format. This format will hereinafter be referred to as BIFS text format. However, for a transport of a data stream in the BIFS format, it is necessary to convert the BIFS text format into a binary format, which will hereinafter be referred to as BIFS binary format. Such a conversion allows simultaneous transportation of a very large quantity of information. The BIFS binary format as well as the conversion from the BIFS text format into the BIFS binary format has been described in the above-cited standard. This standard describes how the scene descriptions must be converted and how the commands must be converted from the BIFS text format into the BIFS binary format. However, the above-cited standard does not describe any device for converting the BIFS text format into the BIFS binary format.  
         OBJECT AND SUMMARY OF THE INVENTION  
         [0009]    It is an object of the invention to provide a device with which a BIFS text format can be converted into a BIFS binary format.  
           [0010]    According to the invention, a data-processing device as defined in the opening paragraph is characterized in that it comprises:  
           [0011]    a scene transcoder for converting the scene description from the first format into the second format, and  
           [0012]    a command transcoder for converting the command from the first format into the second format and having access to information comprised in the scene transcoder.  
           [0013]    According to the invention, a data-processing method as defined in the opening paragraph is characterized in that it comprises the steps of:  
           [0014]    transcoding the scene for converting the scene description from the first format into the second format, and  
           [0015]    transcoding commands for converting the command from the first format into the second format by means of information elaborated during the scene transcoding step.  
           [0016]    According to the invention, a BIFS text data stream is converted into a BIFS binary data stream in the following manner. The data relating to the scene description are converted by the scene transcoder as described in the above-cited standard, and the data relating to the commands are separately converted by the command transcoder as described in the above-cited standard. However, to be able to convert the data relating to the commands, the command transcoder must have access to information which is present in the scene transcoder, such as names and identifiers of nodes. Indeed, each node of the scene description has a name and an identifier. The name is a text which allows identification of a node in a user-friendly manner. The identifier is a number which indicates a location of a node in the scene description. Only the identifier of a node is converted into the BIFS binary format. The commands in the BIFS text format only comprise the names of the nodes. Consequently, the command transcoder needs a table of correspondence between the names and the identifiers of the nodes, which table is comprised in the scene transcoder. Consequently, when a command modifies the scene description, it is not necessary to again convert the whole scene description from the BIFS text format into the BIFS binary format, but only the command. The conversion is thus more rapid, which may be advantageous in applications that are subject to real-time constraints.  
           [0017]    In a particularly advantageous embodiment of the invention, a data-processing device as described above is characterized in that it comprises:  
           [0018]    a graphic interface;  
           [0019]    a compositor suitable for supplying an audiovisual representation of the scene description on the graphic interface;  
           [0020]    modification means connected to said graphic interface and being suitable for effecting at least a modification of said audiovisual representation, and  
           [0021]    editing means suitable for generating at least a command in the first format, said command being representative of the modification.  
           [0022]    This embodiment allows an author to modify a scene description in a user-friendly manner. Indeed, by virtue of the compositor and the graphic interface, the author has at any instant an audiovisual representation of the scene description which he wishes to modify. Using a mouse, a keyboard or any other modification means connected to the graphic interface, he modifies this audiovisual representation as he wishes. Editing means allow commands in the BIFS text format to be generated on the basis of the modifications effected by the author. Such editing means are known to those skilled in the art by the term of authoring tool. Moreover, this embodiment allows use of dynamic commands, i.e. commands generating a modification of the scene description which does not take immediate effect, while conserving its user-friendly aspect. For example, it is possible to carry out a command intended to generate the modification of a node at a given future instant. When one is satisfied with converting the scene description into the BIFS binary format at the instant when the command is carried out, this command would not be taken into account because the modification would only take effect at a future instant.  
           [0023]    In so far as the steps described above can be performed by means of software, the invention also provides a program comprising program code instructions for performing the steps of the method described above when said program is executed on a processor.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0024]    [0024]FIG. 1 is a block diagram illustrating characteristic features of the invention;  
         [0025]    [0025]FIGS. 2 a  and  2   b  illustrate two examples of data-processing devices of the prior art, allowing conversion of data from a first format into a second format;  
         [0026]    [0026]FIG. 3 illustrates a data-processing device in accordance with a particularly advantageous embodiment of the invention;  
         [0027]    [0027]FIG. 4 illustrates a graphic interface which can be used in a particularly advantageous embodiment of the invention;  
         [0028]    [0028]FIG. 5 illustrates a telecommunication network using at least one data-processing device according to the invention. 
     
    
     DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0029]    [0029]FIG. 1 illustrates characteristic features of the invention. A data-processing device according to the invention comprises a scene transcoder  101  comprising a decoder  102  and an encoder  104 , a command transcoder  111  and a multiplexer  131 . Data in a first format  121  contain a scene description  122  and commands  123 ; they are converted into data of a second format  143  by means of the data-processing device.  
         [0030]    In the example under consideration, the first format is a BIFS text format and the second format is a BIFS binary format. The scene description in the BIFS text format  122  is decoded by the decoder  102  which constructs a scene graph  103  in the sense of the standard described above. This scene graph  103  notably comprises a tree structure having nodes. The decoder  102  allocates an identifier to each node stored in a node coding table for each node. Based on the information comprised in all the node coding tables, the decoder  102  establishes a table of correspondence  151  between the names and the identifiers of the nodes. The encoder  104  converts this scene graph  103  so as to generate a scene description in the BIFS binary format  141 . The commands in the BIFS text format  123  are converted into commands in the BIFS binary format  142  by the command transcoder  111 . As a command may consist of, for example, a modification of a node of the scene description  122 , the command transcoder  111  has access to the table of correspondence  151  between the names and the identifiers of the nodes. This correspondence table  151  is stored, for example, in the form of a file in the decoder  102 ; the command transcoder  111  opens this file in order to access the required information. Indeed, the above-cited standard indicates that only the identifier of a node must be converted into the BIFS binary format. As the commands in the BIFS text format only comprise the names of the nodes to be modified, it is necessary for the command transcoder  111  to have access to the identifiers of the corresponding nodes.  
         [0031]    The multiplexer  131  regroups the scene description in the BIFS binary format  141  and the commands in the BIFS binary format  142  for generating the data in the BIFS binary format  143 . An example of the scene description in the BIFS text format  122  will be given below:  
                                                                                                                                   OrderedGroup {                Children [                Shape {                appearance Appearance {                material Material {emissiveColor 1 1 1}                }           geometry DEF G1 Circle {radius 20.0}                }                ]                }                      
 
         [0032]    This scene description in the BIFS text format  122  describes a white circle (referred to as circle G1) having a radius of 20 pixels. An example of a command in the BIFS text format  123  will be given below:  
         [0033]    AT 10000 REPLACE NODE G1 BY Rectangle {size 10 20} 
         [0034]    This command in the BIFS text format  123  signifies that, at a certain instant, the circle G1 is replaced by a rectangle having dimensions of 10 by 20 pixels. In this example, this instant occurs 10 seconds after the start of visualizing an audiovisual representation of the scene description  122 . A user can effect such a visualization on a graphic interface.  
         [0035]    [0035]FIGS. 2 a  and  2   b  illustrate two examples of data-processing devices in accordance with the prior art, allowing a conversion of data from a first format into a second format. In FIG. 2 a , the data in the first format  121  are converted into data in the second format  143  by means of a transcoder  201 . The transcoder  201  converts the scene descriptions as well as the commands from the first format into the second format. Such a transcoder  201  is described in the document “ISO/IEC JTC1/SC29/WG11—title: BIFS/OD Encoder version 4.0—author: Zvi Lifshitz” published in November 1999. A drawback of such a data-processing device is that it is not user-friendly. Indeed, such a device does not allow visualization of an audiovisual representation described by the data in the first format  121 . With such a device it is thus difficult for an author to modify the scene description with the aid of a mouse or a keyboard.  
         [0036]    In FIG. 2 b , the data in the first format  121  are decoded by the decoder  102  which constructs the scene graph  103 . The scene graph  103  may be connected to a compositor and a graphic interface (not shown in FIG. 2 b ), allowing an audiovisual representation of the scene description comprised in the scene graph  103 . The graphic interface may also be connected to means for modifying and means for editing commands (not shown in FIG. 2 b ), allowing an author to modify the audiovisual representation with the aid of, for example, a mouse or a keyboard. The scene graph  103  is then modified. This scene graph  103  is subsequently converted into the second format by the encoder  104  which generates the data in the second format  143 . Such a device is described in a document published by CSELT on Dec. 20, 1999, entitled “IM-1 Two-Dimensional Compositor”. A drawback of such a data-processing device is that dynamic commands cannot be effected. Indeed, as the encoder  104  converts the scene graph  103 , only the information present in this scene graph  103  during such a conversion will be taken into account. If one reverts to the preceding example of the circle G1 which is transformed into a rectangle at a certain instant, when the conversion effected by the encoder  104  precedes the instant at which the modification generated by the command  123  takes effect, it is the circle which is taken into account, and when this conversion follows this instant, it is the rectangle which is taken into account. In order that a modification of the audiovisual representation described by the data in the second format  143  effectively takes place at the instant when it must take place, it is necessary to convert the scene graph  103  immediately after this instant. This generates a larger quantity of data to be transmitted, hence a relatively low data-transmission speed.  
         [0037]    The invention mitigates these drawbacks as is shown in a particularly advantageous embodiment of the invention described with reference to FIG. 3.  
         [0038]    [0038]FIG. 3 illustrates a data-processing device in accordance with a particularly advantageous embodiment of the invention. In addition to the elements described with reference to FIG. 1, such a data-processing device comprises a compositor  301 , a graphic interface  302 , modification means  303  and editing means  304  suitable for generating modification commands in the first format  305 .  
         [0039]    With the aid of the compositor  301 , an audiovisual representation of the scene description comprised in the scene graph  103  can be visualized by an author on the graphic interface  302 . Using the modification means  303 , for example, a mouse or a keyboard, the author can modify this audiovisual representation. The editing means  304  provide the possibility of generating modification commands  305  corresponding to the modifications effected by the author. Authoring tools known to those skilled in the art have the functionalities of the compositor  301 , the modification means  303  and the editing means  304 . Software such as Photoshop and Adobe Premiere are examples of such authoring tools. The modification commands  305  are sent to the decoder  102  and to the command transcoder  111 . With the aid of the modification commands  305 , the decoder  102  updates the scene graph  103  so that the modifications which the author has effected can be visualized on the graphic interface  302 . Such an update of the scene graph  103  on the basis of a command is described in the above-cited standard. This data-processing device allows, on the one hand, modification of a scene graph in a user-friendly manner without having to convert the whole scene graph when a modification is effected, because in this case only the modification command  305  must be converted from the first format into the second format. The quantity of data of the second format  143  transmitted per unit of time is therefore relatively small, which allows relatively high data-transmission speeds. On the other hand, the author may effect dynamic commands with the aid of the modification means  303 . Indeed, the command transcoder  111  may take such dynamic commands into account, which is not the case with the encoder  104  which just converts the scene graph  103  into the second format.  
         [0040]    [0040]FIG. 4 illustrates an example of a graphic interface  302 . The graphic interface  302  comprises a visualization zone  401 , action buttons  402 , a dynamic command zone  403  and a cursor  404 . The visualization zone  401  enables an author to obtain an audiovisual representation of the scene graph  103 . The cursor  404  commanded by the modification means  303  allows, for example, selection of an object in the visualization zone  401  so as to displace this object. Subsequent to such a modification of the audiovisual representation, the editing means  304  generate a command which is intended to modify placement parameters of the node of the scene description corresponding to this object. The action buttons  402  allow, for example, modification of a color of an object selected with the cursor  404 . The dynamic command zone  403  enables the author to define at which instant a modification generated by a command must take effect. The author may define such an instant, for example, by means of a keyboard and then change dimensions of an object of the visualization zone  401 . Such a change of dimensions will only take effect at the instant defined by the author.  
         [0041]    [0041]FIG. 5 illustrates an example of a telecommunication network using at least one data-processing device according to the invention. Such a telecommunication network comprises a data-processing device  501  as shown in FIG. 3, a transmission medium  502  and a reception terminal  503 . The data in the first format  121  may be stored, for example, on a data carrier. As has been described in detail with reference to FIG. 3, they may be modified by an author with the aid of the data-processing device  501  which generates the data in the second format  143 . These data  143  are transported by the transmission medium  502  to the reception terminal  503 . The transmission medium  502  may be a transmission medium used for a telecommunication network, such as Internet, for example, Ethernet. The reception terminal  503  may comprise, for example, a central computer unit and a computer screen or a set top box and a television screen. It comprises means for visualizing the data in the second format  143 , for example, a compositor. Such a reception terminal is known to those skilled in the art. Such a telecommunication network thus particularly enables an author to send audiovisual data to a user having a reception terminal  503  and to modify these data in a user-friendly manner and in real time. For example, in a scene description, one of the nodes may correspond to audiovisual information issued from a camera filming a sports event, and another node may correspond to a score. As a function of the evolution of the sports event, the author may modify the score by modifying the contents of the corresponding node. The user will thus be permanently informed of the score of the event.  
         [0042]    The above description with reference to the Figures illustrates rather than limits the invention. In this respect, several remarks will be made below.  
         [0043]    The description of the Figures applies to the example of the BIFS format. It should be noted that the invention is also applicable to other formats, which may be more advanced than the BIFS format in so far as these formats apply to scene descriptions and commands.  
         [0044]    [0044]FIG. 4 only shows several functionalities of a graphic interface. Such a graphic interface may comprise a large number of functionalities, particularly functionalities corresponding to the commands defined by the format used.  
         [0045]    In principle, it is possible to implement the method according to the invention by means of a suitably programmed integrated circuit. A set of instructions comprised in a programming memory may cause the integrated circuit to perform the different steps described hereinbefore. The set of instructions may be loaded into the programming memory by reading a data carrier such as, for example, a disc on which the set of instructions has been encoded. Reading may be effected by means of a communication network such as, for example, the Internet. In this case, a service provider puts the set of instructions at the disposal of those interested.