WO2001069940A1

WO2001069940A1 - Device for synchronising interactive applications in a television receiver set

Info

Publication number: WO2001069940A1
Application number: PCT/FR2001/000705
Authority: WO
Inventors: Mary-Luc Champel; Ralf Schaefer
Original assignee: Thomson Licensing S.A.
Priority date: 2000-03-15
Filing date: 2001-03-09
Publication date: 2001-09-20
Also published as: FR2806574A1; FR2806574B1; AU2001242550A1

Abstract

The invention concerns the field of broadcasting, transmission and reception of audio-visual programmes containing interactive applications. Said applications need to be synchronised according to the audio-visual content of the event. The inventive method consists in generating a counter internal to the receiver and programme-specific. Said counter is timed by broadcast clock signals. Since said signals can be irregular, the counter is updated by specific descriptors when such irregularities occur. Thus, when displayed, the interactive event-related applications are properly synchronised.

Description

DEVICE FOR SYNCHRONIZING INTERACTIVE APPLICATIONS IN A TELEVISION RECEIVER

The invention relates to the field of broadcasting, broadcasting and receiving audiovisual broadcasts. Audiovisual broadcasts are transmitted from a broadcasting center and received by television receivers.

More specifically, the invention relates to the synchronization of the processing of interactive applications associated with an event during the viewing of said event, which can be broadcast on another stream.

The MPEG-2 standard describes the format for transmitting audiovisual data constituting an event. The data is transmitted in packets and displayed on the television screen. The display is clocked by clock signals emitted by the broadcaster. These clock signals called PCR (“Program Clock Reference”) according to the MPEG-2 standard, have a count value (with a maximum size of 42 bits) of the periods of a signal at 27 MHz. The evolution of PCE values is always increasing.

The interactive applications associated with an event must be triggered at specific times in the viewing of the audiovisual content of this event. These moments are specified in trigger signals which contain a time indication. The interactive applications are generally broadcast on a different channel from that of the events, or are downloaded from a telephone link. Events can contain the same audiovisual sequence viewed in front, then back and again in front. An interactive application linked to such a sequence must be launched regardless of the direction of viewing. The manufacturers fitted the television receivers with a counter synchronized with the PCR signals. This counter called “STC” is constantly updated by the count values included in the PCR signals, and supplies the different elements of the receiver with continuous values between two receptions of PCR signals. The triggering of interactive applications could be done based on this counter. However, the evolution of the counting value of the PCR signals is not always linear. This value can be subject to sudden jumps. In other words, the values can be discontinuous. In addition, the evolution of the PCR values is always increasing, these signals cannot synchronize audiovisual sequences viewed in opposite directions. The positioning of interactive applications when viewing an event cannot therefore, in a reliable manner and in all cases, use the PCR clock signals defined in the MPEG-2 standard.

The invention aims to solve this problem and to allow synchronization of the processing of interactive applications with the visualization of the event with which they are associated.

The invention consists of a method of generating count signals in a digital television receiver, a broadcasting center transmitting first count values to the receiver, said first count values updating a first counter in the said television receiver characterized in that it comprises a first step of transmitting at the level of the data distribution center containing at least a second count value, and a second step of updating a second counter in the receiver with said second count value previously received, the evolution of the second counter being effected from the signals supplied by the first counter. The invention consists of a digital television receiver comprising means for receiving counting signals transmitted from a broadcasting center, a first counter updated with the aid of said counting signals, characterized in that it comprises means for receiving control signals containing second count values, a second counter updated with the second count values, a means for triggering the update and a means for synchronizing the second counter from the values of the first counter.

Equipped with this new time counter, the interactive television receiver has a reliable timing means to start the processing of interactive applications. The new counter uses the PCR broadcast clock signals but, thanks to the emission of specific descriptors which allow it to be updated, it does not have the drawbacks of the broadcast clock signals.

Other characteristics and advantages of the present invention will emerge from the description of the exemplary embodiments which will follow, taken by way of nonlimiting examples, with reference to the appended figures in which:

FIG. 1 represents a decoder for implementing the invention,

FIG. 2 represents a timing diagram for sending the signals having no discontinuity at the level of the PCR values, FIG. 3 represents a timing diagram for transmitting the signals exhibiting a discontinuity at the level of the PCR values,

• Figure 4 shows a timing diagram showing the triggering of interactive services.

FIG. 1 shows the main elements of an interactive television reception system for implementing the invention. This system comprises a receiver (1) connected to a television screen (2), an antenna (3) which receives the broadcasts broadcast from a broadcasting center and optionally, a connection to the telephone network (4). The receiver (1) comprises a central unit (10) running a program recorded in a program memory (11), a data memory (12), an interface (13) connected to the antenna comprising a tuner (TUNER), a demultiplexer and a decoder, a MODEM type interface (14) for bidirectional communication with the telephone network, an audio / video interface (15) for sending the signals to the television screen (2), and a user interface comprising an infrared receiver (16) and a remote control. The central unit receives the data packets transmitted by a broadcaster from the interface (13) and transmits them via the interface (15) to the television screen.

The television receiver receives either the broadcast channel, the telephone link, or any communication channel (unidirectional or bidirectional), the interactive applications and the signals for triggering the processing of these applications. The format for receiving interactive applications and signals is advantageously of the IP (“Internet Protocol”) type. This data can for example be broadcast on the IP channel of the broadcasting network. The applications and the trigger signals are then stored in data memory (12).

According to the present example, the trigger signals contain the following information:

- a time identifier,

- a type of action,

- an application identifier.

The time identifier is a value of a counter incorporated in the receiver which determines the instant of the triggering of an action linked to the interactive application. The creator of the event creates the signals for triggering by requesting the processing of applications at determined instants of the event. The clock created in the receiver must make it possible to find the instants specified by the creator. The type of action performed by the interactive application can be the launching of an interactive application, or the end of an application, or the execution of an electronic magnifying glass, or the display of an icon, or the 'awaiting a user command with display of a corresponding message, ... etc.

The broadcaster emits PCR signals separated by a tenth of a second maximum. Typically, the diffuser emits 20 PCR signals per second. The 42-bit count value contained in these signals is encoded by the broadcaster in the received data packets. Thus, the PCR count value synchronizes the display of the data packets on the television screen. As mentioned above, the STC counter is updated each time PCR signals are received. In a simple way, the value of the STC counter takes the value of the PCR signal received. Between two receptions, the STC counter thus provides continuous values corresponding to the signals

PCR. These values are used by the audio / video interface (15). The evolution of the STC counter is calculated by linear extrapolation between the two previous receptions and the two time values provided by an internal clock to the decoder during the two receptions. The STC counter is advantageously implemented in the form of a software module but can also be produced by an electronic circuit.

As stated in the introduction, the values of the PCR signals may be discontinuous. That is to say that they may present a significant deviation from their regular development over time. Since the STC counter is constantly updated by PCR signals, it has the same discontinuity as the PCR signals. The diffuser being at the origin of this discontinuity and encoding the data packets with these discontinuous values, this does not pose any problem. at the visualization level. The same is not true of the signals triggering the processing of interactive applications, since these signals are linked to the audiovisual content of the event and not at the time of its broadcasting and viewing. It should for example be taken into account that the same sequence is viewed several times, including one backwards. In this case, an interactive application linked to this sequence is triggered several times. It is therefore necessary to define a new synchronization of the trigger signals which is not disturbed by the abrupt discontinuities of the PCR values and of the STC counter.

To overcome this problem, the present invention provides for creating in the receiver a second counter called “NLC” which is associated with a specific interactive service. The receiver has as many NLC counters as there are operational interactive services.

The updating of an NLC counter is carried out using NLC descriptors broadcast by the broadcasting center. The NLC descriptors have the following structure:

The value “Packet identifier” is used to detect the presence in the stream of an NLC descriptor. The values: Network identifier (16 bits), Channel identifier (16 bits), Service identifier ID (16 bits) precisely identify the service broadcasting the event containing the interactive applications to be synchronized. An advantage of the invention being to use the same communication channel for the interactive applications and the NLC descriptors, the triplet previously described makes it possible to make the link between the broadcast event and the NLC counter. According to a first embodiment, the diffuser is capable of detecting the imminent arrival of a discontinuity. In normal times the "FLAG" flag is at "0" indicating the absence of discontinuity. In this case, when the value of the STC counter is equal to "VAL_STC", then the NLC counter is updated with the value "VAL_NLC". Advantageously, the number of bits of the NLC counter is identical to that of the STC counter, but this is not an obligation. The scaling factors of the numerator and the denominator constitute the elements of a quotient whose result "RATIO" is the evolution coefficient between the two counters STC and NLC. Thus, when the value of the STC counter increases by “N”, that of the NLC counter increases by RATIO x N. If the value of the numerator is negative, the value of the NLC counter decreases. This is a sign that the audiovisual content is viewed backwards. The values VAL_STC, VAL_NLC and the scaling factors are used to initialize the NLC counter when it is started up. We will see it later, in some cases, the scale factors and the VAL-STC value can be omitted. The relation linking the values of the STC and NLC counters between two updates is of affine type. Thus, the values of the NLC counter correspond to the equation: NLC counter value = RATIO x (STC counter value) + OFFSET. The reception of a first complete NLC descriptor (the four identifiers, the values of STC and NLC, the scale factors and the flag) initializes the NLC counter.

The implementation of the NLC counter gives it an autonomous character with respect to the STC counter. However, an alternative embodiment consists in not actually using a counter but the affine relationship which unites the NLC and STC values and in recalculating the RATIO and OFFSET values during the processing of each descriptor received. This variant avoids the implementation of a counter but requires very often to calculate the NLC value to trigger interactive applications at the right time. Since a television displays 25 images per second, and an interactive application can be triggered when viewing a single image, the calculation must be performed at least 25 times per second.

FIG. 2 shows an example of a chronology of events in the absence of discontinuity of the PCR values. In the example, the PCR values are: 1000, 1080, 1180, 1320, ... 1760. They are not sent at regular intervals. Since the evolution is regular over time, the difference between two consecutive values depends on the duration of the interval. The evolution of the STC internal counter value is shown below. Its value is updated each time PCR signals are received. Below, the broadcast by the broadcaster of three NLC descriptors (1), (2) and (3) is shown. The first descriptor is issued when the value of the STC counter is approximately equal to 1040. This descriptor contains the following parameters: STC = 1100, NLC = 300 Ratio = ^_1/2 and FLAG = 0. The receiver stores this data in memory and waits for the moment when the STC counter takes the value 1100. At this moment, the NLC counter is initialized to "300". Then, the value of the NLC counter changes half as fast as that of the STC (Ratio = Vz). When the counter STC has approximately the value 1140, the second descriptor NLC is received. This descriptor contains the following parameters: STC = 1340, NLC = 420, Ratio = -1/2 and FLAG = 0. Au when the STC counter reaches the value "1340", the NLC counter is initialized to "420". The drawing shows a reversal of the direction of evolution of the NLC counter. From this moment, the event is viewed in reverse. For example, if the audiovisual sequence shows a racing car in a turn, from the moment STC = 420, the car starts in reverse on the television screen. The speed of evolution of the NCL values is half that of the STC values (| RATIO | = Y ₂ ).

When the STC counter has approximately the value 1600, the third NLC descriptor is received. This descriptor contains the following parameters: STC = 1600, NLC = 290, Ratio = 1/1 and FLAG = 0. As before, when the STC counter reaches the value "1600", the NLC counter is initialized to "290" . Updating the NLC counter with a value that seems equal to the one it already has, allows small time drifts to be corrected. After the instant STC = 1600, the value of the NLC counter evolves at the same speed as that of the STC (RATIO =%) and in the same direction of growth.

Suppose that the receiver has previously received a trigger signal indicating the processing of an interactive application (X) at time NLC = 350. This equality occurs three times, the first time when STC = 1200, the second STC = 1480 and the third STC = 1660. The interactive application is therefore triggered three times. In the previously cited example of a car race, suppose the car loses its spoiler in the middle of the turn. The creator of the event wishes to highlight the loss of the fin by launching an electronic magnifier. This application is triggered three times. In this first embodiment, once a descriptor has been processed, it is erased from the memory.

When the broadcaster knows that a discontinuity will soon appear in the chronology of the values emitted in the PCR signals, the flag of an NLC descriptor preceding the discontinuity of the PCR / STC is positioned at "1". On the next reception of a PCR signal presenting a discontinuity, the NLC counter is updated with the value VAL_NLC indicated. The value VAL_STC is not taken into account.

FIG. 3 shows an example of a chronology of events with a discontinuity of the PCR signals. In this example, the PCR values are: 1000, 1080, 1180, then the value is suddenly 1440 while regularly, it should have been around 1280. Then they then continue regularly: 1520, 1640, 1740. The evolution of the value of the internal counter STC is shown below. It shows the discontinuity of the PCR signal by the direct passage from the value 1280 to the value 1440. Below, the emission by the broadcaster of three NLC descriptors is shown. The first descriptor is issued when the value of the STC counter is approximately equal to 1020. This descriptor contains the following parameters: STC = 1060, NLC = 300, Ratio = Vz and FLAG = 0. When the STC counter reaches the value 1060, the NLC counter is initialized to "300". Then, the value of the NLC counter changes half as fast as that of the STC (Ratio = Vz). The second descriptor is issued when the value of the STC counter is approximately equal to 1200. This descriptor contains the following parameters: NLC = 410, Ratio = Vz and FLAG = 1. The value of the discontinuity flag makes it possible to manage a possible discontinuity in the emission of the next PCR signals. When the receiver receives the PCR signal indicating the value 1440, the NLC counter keeps the value 410. Only the offset between the values of the STC counter and those of the NLC counter is modified. Since the RATIO value is not modified, the evolution curve of the NLC counter shows no modification when the values of the PCR signal become discontinuous.

Later, a third NLC descriptor is issued, it contains the following parameters: STC = 1820, NLC = 600, Ratio = 1/1 and FLAG = 0. The values of the NLC counter do not have any discontinuity, now they change to the same speed as that of the STC counter (Ratio = 1/1). In this way, the broadcaster can monitor the evolution of the values of the NLC counter, by synchronizing it with the PCR signals and by updating it with descriptors when a divergence occurs or when the PCR signals are no longer regular.

A first alternative embodiment consists in that the receiver calculates itself the evolution coefficient between the two counters STC and NLC. The scaling factors of the numerator and the denominator then become useless and no longer need to be issued. The calculation method is as follows: two descriptors containing the pairs of values (NLC1.STC1) and (NLC2.STC2) are received in a receiver. Let the deviations: ΔSTC = STC2 - STC1 and ΔNLC = NLC2 - NLC1. The ΔNLC / ΔSTC ratio defines the value of the ratio previously calculated from the evolution speeds of the NLC counter with respect to the STC counter. The NLC counter is updated with the new report when the STC counter takes the value STC2. This variant obliges to keep in memory the previous descriptor. It can only be used in the absence of discontinuity (FLAG = "0"). If the PCR values show a discontinuity, the difference ΔSTC is no longer significant and the ratio ΔSTC / ΔNLC can no longer be calculated. In this case, the distributor must indicate with the numerator and the denominator the new ratio.

Figure 4 shows the triggering of interactive services during the normal evolution of the NLC counter.

In the first descriptor, the value of NLC is 30 and STC: 120. In the second descriptor, the value of NLC is 70 and STC2: 200. The differences are: ΔSTC = STC (200) - STC (120) = 80 and ΔNLC = NLC (70) - NLC (30) = 40. The ratio ΔNLC / ΔSTC (= 80/40) is equal to Vz (RATIO = Vz). In the example, an interactive application is triggered at the value 90. When the NLC counter reaches this value, the application is triggered. Yes a discontinuity occurs when the STC counter takes the value of approximately 240, it cannot disturb the processing of the interactive application which is synchronized by the NLC counter.

A second improvement consists in that the receiver has the means to detect the discontinuity. In this case, the updating of the NLC counter no longer takes place during the next reception of PCR signals, but when the decoder effectively detects that the value of the PCR signal which has just been received has a discontinuous nature. Detection can be carried out in the receiver using an internal clock in the form of an integrated circuit for example. The values provided by this clock make it possible to establish the relationship between the evolution of the value of the clock and that of the PCR signals. This report is recalculated during each PCR reception from the time difference since the previous reception and the time indicated by the clock. If the value of this ratio changes suddenly, the last reception of the PCR presents a discontinuity compared to the previous one.

The invention is of course not limited to the embodiments which have just been described. In particular, it makes it possible to synchronize all applications presenting an audiovisual character during the viewing of an event.

Claims

1. Method for generating count signals in a digital television receiver, a broadcasting center transmitting first count values to the receiver, said first count values updating a first counter in said television receiver characterized in that it comprises a first step of transmission at the level of the data distribution center containing at least a second count value, and a second step of updating a second counter in the receiver with said second previously received count value, the evolution of the second counter being effected from the signals supplied by the first counter.

2. Method for developing counting signals according to claim 1 characterized in that the data transmitted by the central office include a first count value and in that the second step of updating the second counter occurs when the value of the first counter corresponds to said first received count value.

3. Method for developing counting signals according to claim 1 characterized in that it comprises a step of receiving data transmitted by the central comprising a second count value and an indicator announcing an irregularity of the next first count value transmitted by the central office, and a third step of updating the second counter with said second count data received, said third step intervening when the next first count value is received.

4. Method for developing counting signals according to claim 1 characterized in that it comprises a step of receiving data sent by the central office comprising a second count value and an indicator announcing an irregularity of the next first count value sent by the central office, and a third step of updating the second counter with said second received counter data, the said third step occurring when the receiver detects that the last first count value received has an irregular character.

5. Method for developing counting signals according to any one of the preceding claims, characterized in that it comprises a step of calculating the evolution coefficient between the values of the first counter and the values of the second counter, prior to each second update step.

6. Method for developing counting signals according to any one of the preceding claims, characterized in that it comprises a step of triggering at least one interactive application activated when the second counter reaches or exceeds a determined value.

7. A digital television receiver comprising means for receiving counting signals transmitted from a broadcasting center, a first counter updated using said counting signals, characterized in that it comprises means for receiving control signals containing second count values, a second counter updated with the second count values, means for triggering the updating of the second counter and means for synchronizing the second counter from the values of the first counter.

8. Digital television receiver according to claim 7 characterized in that it comprises a comparator between the values of the first counter and a value previously received in a control signal and stored in the receiver, the update of the second counter is activated when the two values correspond.

9. Digital television receiver according to claim 7 characterized in that it comprises means for receiving an indicator of irregularity of the counting signals received from the reception means, the updating of the second counter is activated during the reception of counting signals which follows the reception of said indicator.

10. Digital television receiver according to claim 7 characterized in that it further comprises a means of detecting an irregularity of the counting signals received from the reception means, the updating of the second counter is activated upon detection of an irregularity.

11. Digital television receiver according to any one of claims 7 to 10 characterized in that it comprises means for processing interactive applications, said processing means being activated when the value of the second counter reaches a determined value.