HK1004179A - Method of video information transmission as well as an information carrier, a device for receiving and a device for transmitting video information - Google Patents

Description

Method for transmitting video information, information carrier, and apparatus for transmitting and receiving video information

The invention relates to a method of transmitting video information intended for reproduction on a display by means of an information signal representing the video information, the video information comprising basic information and overlay information (overlay information) associated with the basic information.

The invention further relates to an information carrier on which an information signal is recorded, which information represents video information intended to be reproduced on a display, which video information comprises basic information and overlay information related to the basic information.

The invention further relates to a device for information transmission and a device for information reception using the method.

Such a method, information carrier and device are known from WO 92/00647. The video signal, whose basic information is analog video information, is transferred via a laser disc. Digitally encoded Subtitle (Subtitle) information is recorded on the compact disc as overlay information separated from the video information in the form of subcodes of digital audio signals. When this subcode information is generated, the subtitle information is read from the file, which also indicates the time at which the text is to be displayed. And the subtitles are recorded in the form of subcodes of the audio signal corresponding to the moment. Upon reproduction, the subtitles are displayed once restored from the subcodes.

A problem of the known method is that the subtitles displayed on the television screen stay until the next subtitle is received, for example in case of changing scenes the subtitles may remain on the screen for too long. This may be particularly the case when the next subtitle is not received, for example when the disc is used in a special operating mode such as fast forward or fast reverse.

It is an object of the invention to provide means for transmitting video information such that the reproduction of overlay information is independent of the information to be transmitted at a later stage.

According to a first aspect of the invention, the exemplary method as indicated in the opening paragraph is characterized in that: the overlay information includes time information indicating a time period during which the overlay information is to be displayed. The method according to the invention has the advantages that: for example, the overlay information may be displayed on the television screen for any desired period of time, which makes it possible to display the overlay information more closely related to the base information.

An embodiment of the method according to the invention is characterized in that: the time information comprises a duration indicating the duration calculated from the instant the overlay information may appear on the display. An advantage of this embodiment is that the given duration can be simply calculated during the display. A further advantage is that it is obtained in a fast forward or fast reverse mode, where the overlay information can still be displayed for the original duration.

A further embodiment of the method according to the invention is characterized in that the basic information comprises a time code for indicating the relative time of the basic information, and in that the time information comprises an elimination time for indicating a relative moment after which the specific overlay information is to be eliminated from the display. This embodiment has the advantage that during reproduction the duration can be simply determined by comparing the elimination time with the relative time of operation, and the overlay information is eliminated from the display when an earlier relative time is found.

A further embodiment of the method according to the invention is characterized in that the basic information comprises video information and overlay information comprising graphics information. This embodiment has the advantage that the basic information is a moving image and the overlay information is a graphical picture that can be selectively overlaid.

A further embodiment of the method according to the invention is characterized in that the overlay information comprises subtitle text. An advantage of this embodiment is that the subtitle text can be selectively overlaid on the basic information.

A further embodiment of the method according to the invention is characterized in that the basic information comprises digital, compressed video information. An advantage of this embodiment is that both basic information and overlay information, represented by numerical symbols, can be transferred in a similar manner.

According to a second aspect of the invention, a typical information carrier as indicated in the opening paragraph is characterized in that: the overlay information includes time information indicating a time period during which the overlay information is to be displayed. The information carrier according to the invention has the advantages that: for example, the overlay information may be displayed on the television screen for a desired duration without regard to other information to be read after the particular overlay information. It is an advantage for the provider of the video information that the duration can be determined irrespective of the display device.

According to a third aspect of the invention an apparatus comprises means for receiving an exemplary information signal as indicated in the opening paragraph, and combining means for generating a video signal representing basic information and combined with overlay information, characterized in that the apparatus comprises means for retrieving time information from the information signal, and in that the combining means are arranged for displaying the overlay information as a function of the time information. The advantages of the device according to the invention are: for example, for a desired duration of time to display information on a television screen, this overlay information may be combined with the base information without the overlay information having to take into account other information to be received after this particular overlay information.

According to a fourth aspect of the invention, an apparatus comprises generating means for generating an information signal of the type indicated in the opening paragraph, and means for transmitting the information signal, characterized in that the apparatus comprises means for generating time information, and the generating means are arranged for adding the time information to the overlay information. The advantages of the device according to the invention are: for example, during transmission, it can be determined how long the overlay information is displayed with the base information without the need to include the information in the information signal at a later time.

These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter.

In the drawings:

FIG. 1 shows a video information television screen displayed;

FIG. 2 shows a system for transmitting video information;

FIG. 3 shows a duration-information table;

fig. 4 shows an information carrier;

FIG. 5 shows an apparatus for receiving video information;

fig. 6 shows a device for reading an information carrier;

FIG. 7 shows an apparatus for transmitting video information; and

fig. 8 shows an apparatus for transferring video information via an information carrier.

Elements corresponding to those described in the previous figures are given the same reference characters.

Fig. 1 shows a television screen 1 on which video information is displayed. This video information contains basic information 2 displayed on the entire television screen surface as shown in fig. 1 a. The basic information 2 may be formed of a moving image such as a movie image or a television program. The basic information may also include animated or still photographic images. Fig. 1b shows the same basic information 2, but on top of it the graphical information 3 is displayed as overlay information. For example, the basic information 2 may be kept on the background as well, and a new note may be repeatedly displayed as the overlay information. Fig. 1c shows subtitle text 4 as overlay information, which may be used for example for movies. In a television system, overlay information is combined with base information prior to transmission, and this overlay information is transmitted with each image of the base information. By transmitting the cover information in a separate manner, for example as is implemented in said WO92/00647, more than one piece of cover information can be transmitted together, so that the user can for example choose from several languages, or omit subtitles 4 altogether.

Fig. 2 shows a system for video information transfer. Video information is transmitted, for example, by an information signal such as a television signal, by a digitally modulated signal of a network, or by a magnetic tape such as a VCR (video cassette recorder), by a signal recorded on an optical disk such as a laser disk or a digital video disk. The device 21 for transmitting information signals will transmit video information signals to the receiving device 23 by means of the transmission channel 22. The receiving device 23 reproduces this video signal for the user. The information signal comprises at least an analog video signal, for example of PAL or NTSC, or an MPEG-1 or MPEG-2 digitally encoded and compressed video signal, representing the basic information. Furthermore, the information signal comprises a representation of the cover information encoded by means of information symbols, which symbols are separately recoverable from the basic information. The cover information page will be replaced if the next cover information page is received after a period of time. Another alternative is to transmit overlay information with each new image. However, this is at the cost of greater transmission capacity, particularly when, for example, subtitles in multiple languages are to be transmitted. In video information, the symbols may be transmitted together in the form of a digital signal during the horizontal or vertical blanking interval, and in a fully digitized stream the different user data streams may be multiplexed, for example by further packing the digital data streams into packets and providing them with a header indicating the type of information. In the case of MPEG-2, the video information is encoded as described in International Standard ITU/ISO 13818-2. In ITU/ISO13818-1 it is described how an elementary stream of encoded video data is multiplexed with other encoded data, e.g. representing audio and subtitles, into an MPEG-2 program stream. Information of a type not specified by MPEG is included in the "private package" in a format that can be selected at will. MPEG-2 recognizes the packet with the additional header of the prescribed format as "private stream 1", and the packet without the prescribed format as "private stream 2". Subtitles, for example, may be included in packets of private stream 1; these packets may contain an optional presentation time stamp indicating the start of presentation on the television screen. The subtitles are not replaced until the presentation time of the next subtitle has come.

In the information signal according to the invention the overlay information contains time information indicating a period during which the overlay information is to be displayed on the television screen. The above-mentioned symbols intended for covering information are included in the information signal, for example in private packets of an MPEG-2 stream. These packets currently contain a time code. An example of an information signal according to the invention with a time code that can be added to the overlay information to control the display of the overlay page is given in the table of fig. 3. The number of bits available per parameter is given. page _ start _ code specifies the beginning of a page, page _ data _ length specifies the total amount of information for the page, and there is room for other control information, e.g., duration 25. The time code may specify a number of seconds, for example, a duration (or portion thereof). Different suitable time units, such as frame number or available system clock units, e.g. 90KHz of MPEG, may also be selected. This period starts when the overlay information is displayed on the television screen, for example after the presentation time stamp of MPEG-2.

In the case where the basic information signal contains a time code indicating the relative time of the basic information, there is an indication of the time available for the basic picture to be displayed. In the case where the time information may be indicated by a clearing time, which indicates a (relative) moment from which the particular overlay information is no longer displayed on the television screen, MPEG-2 time information may be included in, for example, an extension of the packet header or in the user data.

Fig. 4 shows an optically readable information carrier 30 in the form of a disc, such as a CD or a laser disc. An information signal representing video information to be displayed on a television screen is recorded on the spiral or concentric track 31. A description of reading CDs can be found in the title "optical disc System principles" (ISBN 0-85274-785-3) written by Brouwhuis et al. The video information and information signals are described with reference to fig. 1 and 2, and the overlay information contains time information indicating the duration during which the overlay information is to be displayed on the television screen, in the manner described with reference to fig. 3.

Fig. 5 shows an apparatus for receiving video information, such as a satellite receiver or a television signal decoder, also referred to as a set-top-box (set-top-box). The transmitted signal reaches the receiving means 42 via an antenna system 41 (not part of the apparatus) or via a cable connector, where the information signal is recovered and sent to combining means 43, where the basic information is combined with the overlay information to generate a video signal. The information signal is also sent to means 44 to recover the time information, while these means 44 give a command to the combining means 43 at the appropriate instant according to the time information to remove the covering information from the television screen. The video signal may be provided to a user via output 46. In a further embodiment the device further comprises a display 45 on which the image can be directly reproduced.

Fig. 6 shows a device for reading an information carrier 30, such as for example a CD. The apparatus comprises scanning means 51 for scanning the track 31 by the laser beam. The apparatus corresponds more to the apparatus of fig. 5, the received signal goes to the receiving means 42 and then to the combining means 43 and means 44 for recovering the time code, the processing of the information signal having been described with reference to fig. 5.

Fig. 7 shows an apparatus for transmitting video information, such as a television transmitter. The video information is fed to an image generating means 62, the basic information being fed via an input 60 and the overlay information being fed via a separate input 61. The image generation means 62 encodes the video information and generates an information signal. The information about the display of the overlay information is fed via an input 67 to time code generating means 63 which generate a time code for the duration of the display. The duration may be predetermined and stored in a computer file, for example, but the duration may also be derived automatically from the length of the subtitles or given manually by an operator. In the multiplexer 64 the generated time code is added to the covering information, after which the entire information signal is amplified in the transmitting means 65 for transmission via the antenna 66. If two languages are available for the subtitle text of the film, the time code generating means 63 will generate time codes for the two languages, respectively. In the receiver, a choice can be made between no subtitles and subtitles in any one language.

Fig. 8 shows an apparatus for transferring video information via an information carrier, such as a CD-ROM. A master information carrier is first produced using the apparatus shown, from which a large number of information carriers are then copied by means of a conventional coining process (not shown). The complete information signal is generated by means of the generating means (62, 63, 64) described with reference to fig. 7. The channel encoding unit 70 encodes the information signal in a conventional manner for disc-shaped carriers and supplies this information to the transmitting unit 71. The transmitting unit 71 acts on the mother information carrier 73 by means of a transmitting beam 72, for example a high intensity laser beam. A system controller (not shown) of conventional type provides speed control of the disk rotation and positioning of the emitter units 71 on the tracks 31. For further explanation of the CD system, the topics set forth with reference to FIG. 4 may be consulted. In another embodiment a similar device is adapted for recording information signals on a record carrier which is directly re-recordable, e.g. re-recordable CD, VCR tape or optical tape.

Embodiments of the apparatus are not limited to the examples of fig. 5, 6, 7, and 8, but include any apparatus for receiving and/or transmitting video information, where the overlay information contains time information specifying a display duration.

Claims (17)

1. A method of transmitting video information intended to be reproduced on a display by means of a signal representing the video information, the video information comprising basic information and overlay information related to the basic information, characterized in that the overlay information comprises time information, which time information indicates a time period during which the overlay information is to be displayed.

2. A method according to claim 1, characterized in that the time information comprises a duration indicating the duration calculated from the instants at which the overlaid information is likely to appear on the display.

3. A method according to claim 1 or 2, characterized in that the basic information comprises a time code to indicate the relative time of the basic information; and in that the time information includes an erasure time to indicate a relative moment after which the particular overlay information will be erased from the display.

4. A method as claimed in claim 1, 2 or 3, characterized in that the basic information comprises video information and the overlay information comprises graphics information.

5. Method according to one of the claims 1 to 4, characterized in that the overlay information comprises subtitle text.

6. Method according to one of the claims 1 to 5, characterized in that the basic information comprises digital, compressed video information.

7. Information carrier having an information signal recorded thereon, which signal represents video information intended to be reproduced on a display, which video information comprises basic information and overlay information related to the basic information, characterized in that the overlay information comprises time information, which time information indicates a time period during which the overlay information is to be displayed.

8. An information carrier as claimed in claim 7, characterized in that the time information comprises a duration indicating the duration calculated from the instants at which the overlay information is likely to appear on the display.

9. An information carrier as claimed in claims 7 and 8, characterized in that the basic information comprises a time code to indicate the relative time of the basic information; and in that the time information includes an erasure time to indicate a relative moment after which the particular overlay information will be erased from the display.

10. An information carrier as claimed in claim 7, 8 or 9, characterized in that the basic information comprises video information and the cover information comprises graphics information.

11. Information carrier as claimed in one of the claims 7 to 10, characterized in that the overlay information contains subtitle text.

12. Information carrier as claimed in any one of claims 7 to 11, characterized in that the basic information comprises digital, compressed video information.

13. Apparatus for use in a method as claimed in one of the claims 1 to 6, the apparatus comprising means (42) for receiving an information signal and combining means (43) for generating a video signal representing a combination of basic information and overlay information, characterized in that the apparatus comprises means (44) for recovering time information from the information signal, and in that the combining means (43) are arranged for displaying the overlay information as a function of the time information.

14. Device according to claim 13, characterized in that the receiving means comprise means (50, 51) for reading the information signal from the information carrier (30) of one of claims 7 to 12.

15. A device according to claim 13 or 14, characterized in that the device comprises a display (45).

16. Apparatus for use in a method as claimed in one of the claims 1 to 6, the apparatus comprising generating means (62, 64) for generating an information signal, and means (65) for transmitting the information signal, characterized in that the apparatus comprises means (63) for generating time information, and in that the generating means (64) are arranged for adding the time information to the overlay information.

17. Apparatus according to claim 16, characterized in that the apparatus comprises means (70, 71, 72) for recording an information signal for generating an information carrier as claimed in one of claims 7 to 12.