TELEVISION SYSTEM WITH MULTIPLE
VIDEO PRESENTATIONS ON A SINGLE
CHANNEL
FIELD OF THE INVENTION
The present invention is generally directed to a television system which is capable of concurrently distributing multiple video presentations having different video information content over a single television channel for receipt by different respective viewers. For example, a television system in accordance with the present invention can distribute a broadcast video presentation as well as a plurality of interactive presentations from a central presentation system, to respective viewers with associated television set and terminal, by means of a single television channel.
BACKGROUND OF THE INVENTION
An interactive still frame television distribution system is disclosed, for example, in the U.S. Pat. No. 4,734,764 and U.S. Pat. No. 4,924,303. Such systems are particularly suited for interactive video services such as home shopping, financial transactions, education and the like. Generally speaking, in this type of system a viewer sends an indication to a central location describing a video presentation which he desires to receive, e.g. houses being offered for sale by a real estate service. Video frames which show the available houses are individually retrieved from a suitable video presentation which enables it to be retrieved from a suitable video storage medium, and each frame is labelled with an identification code which enables it to be retrieved by the viewer who desires to see it. Other viewers can independently request other presentations available on the system. All of the frames selected by the various viewers are multiplexed onto a transmission medium, such as the trunk cable of a cable television system, and transmitted at the standard television frame rate, e.g. 30 frames per second under the NTSC standard, over a channel associated with the video presentation service. Frame stores are positioned at various locations along the length of the transmission medium, and each is provided with a match code, for example an address. When a video frame is labelled with the match code of a particular frame store, that frame store identifies the frame, stores it in a memory, and then continually retransmits the stored frame at the standard television frame rate to the viewer's television receiver. The continually transmitted frame appears as a still frame on the viewers's television receiver. When the next frame in the presentation is required, this frame is retrieved, labelled with the appropriate code, and transmitted to the frame store for display in the same manner. This process is repeated for all the frames in the still-frame presentation.
A sequence of frames may be sent for each still-frame presentation. If still frames are delivered at sufficient rate, the presentation takes on the appearance of reduced motion rather than distinct still frames. For example, if frames are sent at a rate of 6 per second, 5 concurrent user presentations are possible over a single television channel (having 30 frames per second capacity) with reduced motion. Additional processing within the frame store unit can interpolate several images to display additional images, with the object of producing the appearance of smoother motion.
With the increasing acceptance of the value of interactive television services, there is a clear benefit to the industry to provide an efficient transmission medium for these services. The interactive television systems as disclosed in the U.S. Pat. No. 4,734,764 and U.S. Pat. No. 4,924,303 require a
dedicated television channel to offer interactive services. The high cost of dedicating a television channel solely to an interactive service is viable only for the largest of such services. The present invention enables interactive services to begin with a small amount of channel capacity at a fraction of the channel costs.
Additionally, many television telecasters such as cable, direct broadcast satellite (DBS) and wireless cable companies have reached the limit of their channel capacity and are unable to meet the demand of the proliferation of new programming sources. The result is that interactive service providers are unable to acquire the "full" channel required to offer their services. The present invention enables the sharing of channel capacity enabling an interactive medium for broadcasters and information providers. Furthermore, it is highly desirable to include interactive capabilities with many of these broadcast services. As an example, a Public Broadcast Service (PBS) educational video broadcast could simultaneously support a plurality of viewer requested interactive video presentations for example testing and additional information on a particular subject reviewed in the broadcast. Combining these applications onto one channel would save the cost of an additional channel while providing the benefits of interactivity.
Accordingly, it is an object of the present invention to provide a television system which expands the program capacity of each channel of the television system by distributing at least two distinct presentations concurrently on a single channel. It is a further object of the present invention to address the above-mentioned needs by providing a television system which is capable of distributing multiple interactive and broadcast video presentations, to different respective viewers by means of a single television channel, including the combination of full motion, reduced motion and still-frame video presentations. It is a further object of the present invention that the combination of presentations be dynamically variable so that the system can respond to changing presentation requests over time.
SUMMARY OF THE INVENTION
The present invention provides a television system which increases the capacity of television channels by exploiting the fact that certain presentations do not require the full image capacity of a dedicated television channel and therefore the excess capacity can be used to distribute images of additional presentations over that channel. A television signal having multiple video presentations is transmitted over a single television channel. In an exemplary embodiment of the invention, one video presentation could comprise a motion video program and other presentations could pertain to still-frame interactive video services. The television signal is produced by a multiplexer which combines the still-frame interactive video images and motion video images into a standard (such as NTSC) sequence of images for transmission.
In one embodiment of the invention, each of the interactive video images has an identification associated therewith so that these images can be distinguished from the full motion video images, which have a distinct associated identification. A user terminal which receives the transmitted television signal can be selectably operable to display different presentations. A selection corresponds to one of the video presentations transmitted in the television signal, and causes a television receiver connected thereto to display only the corresponding video presentation. In the specific example described above, the terminal can display either the
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motion presentation or a still-frame interactive presentation. To display a selected television signal corresponding to the associated selected presentation, the terminal identifies the video images of the presentation, stores the selected images, and displays them on an associated television set. Other 5 applications of the invention are also possible. The television signal could combine two or more motion video presentations wherein the content is such that each presentation can be displayed at less than the standard television rate without significant quality loss to the viewer. For example, 10 a movie broadcast could be allocated more or less fields depending on many factors as an example, the number of interactive fields to be transmitted, the motion quality or combination of the above. In the case of an educational program containing a "talking head" the video broadcast 15 could be reduced to 15 fields per second leaving the remaining 45 fields for interactive presentations.
The interactive information to be combined with the motion broadcast can be user activated wherein user requested interactive instructions between a user at the 20 terminal end and the presentation system are carried out via the use of a communication link such as a telephone line. Interactive information is requested by the user at the terminal end using a keypad device such as a wireless infrared remote control, computer keyboard, or telephone 25 keypad. A further extension of the invention provides for the storage of the motion programming on the interactive system whereby the user controls the broadcast of the motion programming through the communications link.
A second method of interactive operation is disclosed 30 whereby interactive images are multiplexed with the broadcast video presentation and continuously transmitted as a plurality of images to all remote terminals. This group of preselected interactive images is referred to as a carousel of images and is similar to the carousel concept employed in 35 teletext based systems. The present invention discloses the transmission of video image(s) rather than teletext graphics and text although the present invention could also transmit video images of teletext generated graphics and text. This second method of interactive operation utilizes the same 40 keypad device as previously described but does not require a communications link to the interactive presentation system as disclosed with user requested interactive presentations.
The invention extends to a digital as well as analog (such as NTSC) transmission format where images or sequence of images are labelled with an identifier. Under a digital television format, additional digital processing such as image compression permits even greater dynamic variation in the trade-off between image transmission rate, image resolution and degree of compression.
With a digital format, broadcast video presentations could be stored on the interactive video presentation system and telecast based on a predetermined schedule or activated and controlled by a user at the terminal end. 55
The foregoing features of the invention, as well as the advantages provided thereby, are explained in greater detail hereinafter with reference to preferred embodiments illustrated in the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS 60
FIG. 1 illustrates a specific example of a sequence of image frames with certain fields being repeated to provide a full motion video sequence;
FIGS. 2A and 2B respectively illustrate a transmitted 65 combined image sequence and a reconstructed motion video sequence;
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FIG. 3 is a block diagram of an interactive television system which operates according to the principles of the present invention;
FIG. 4 is a detailed block diagram of the terminal utilized at the user's end according to the present invention;
FIG. 5 is a more detailed block diagram of the presentation system in the interactive television system and;
FIG. 6 is a more detailed block diagram of the picture multiplexer and associated hardware according to the present invention.
DETAILED DESCRIPTION OF THE
ILLUSTRATED EMBODIMENTS
The present invention achieves increased capacity for a television channel by producing a television signal having video images from at least two distinct video presentations incorporated into a signal transmitted over a single television channel. As used herein, the term "video presentation" is employed to identify video image sequences which correspond to motion television presentations as well as stillframe video presentations. In its transmitted form, the video presentation could comprise an analog video signal or digitally encoded video data. Furthermore, the encoded video data could be in a digitally compressed format.
A standard television signal is comprised of multiple successive images. When the television signal is transmitted in an analog form, each image is called a frame. Under the NTSC standard, for example, video images are transmitted to a standard television receiver at a rate of 30 image frames per second. A single image frame presents a video-quality still image. Each image frame actually consists of two image fields which are interleaved to increase the vertical resolution while reducing flicker in the displayed picture. The image field rate is therefore 60 fields per second. The two interleaved fields are comprised of a plurality of scan lines referred to as the vertical blanking interval (VBI) and a larger plurality of scan lines containing the video signal to be converted to a video image on the television screen.
When the television signal is transmitted in a digital format, each image is sent in a data block that corresponds to one field or frame. Digitally transmitted image data typically does not include a 'vertical blanking interval' as in the analog standards. However, each data block would typically include a header record to identify that image. In a compressed digital video signal, the image rate may be substantially higher than the analog rate of 60 image fields per second. For example, current technology can digitally compress a still video field into 10 kbytes of data, and provide a digital transmission capacity of 20 Mbps (2.5 Mbytes/s) in an NTSC channel. Thus, 250 images may be transmitted every second on a single television channel. This capacity is sufficient to carry various combinations of still and motion presentations. For example, 250 images per second is sufficient to carry 4 full-motion programs on a single channel or support 2,500 interactive viewers requesting still frames every 10 seconds. The present invention provides for various combinations of still and motion presentations. For example, a combination could entail one full-motion broadcast video presentation of 60 fields per second combined with 190 images per second of interactive images whereby the 190 images could be assigned such that 20 images per second could be allocated to the image carousel while the remaining 170 images per second could be dedicated to user requested interactive presentations relating to 1,700 users with an average of 10 seconds between images. The number of images dedicated to the to
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each of the interactive services and video presentation is dynamic. For example, the number of images allocated to the carousel can increase or decrease according to the number of user requested presentations. Technology advances are anticipated to increase channel capacity and 5 reduce compressed image sizes, resulting in higher image rates within the transmission channel.
The television system of the present invention has the capability to transmit a signal over a single television channel having images that are respectively associated with 1° at least two distinct video presentations. For example, the transmitted signal may comprise a sequence of images wherein every other image is associated with a first broadcast video presentation and the remainder are associated with a interactive video presentations. This concept will be :5 further explained with reference to a specific example illustrated in FIGS. 1,2A and 2B. To facilitate an understanding, this particular example pertains to an analog video signal comprised of image frames.
Certain types of full motion presentations, such as 20 movies, consist of 24 image frames per second. To convert a movie to a video signal for transmission and display in a typical television system, the 24 image frames are expanded to 30 image frames by the repetition of 1 video field for every 2 images as illustrated by way of example in FIG. 1. 25 As shown in FIG. 1, a sequence of image frames corresponding to image 1, image 2, image 3, and image 4 are transmitted. Each image frame comprises two distinct fields as previously noted, e.g. image 1 includes a first field Ml-1 and a second field Ml-2. The actual conversion from 24 to 30 30 image frames per second is illustrated by the repetition of a field of image 1 and Ml-3 and a field of 3 as M3-3. Preferably, the first field is repeated to maintain full vertical resolution. The repeated field contains the same information as the previously transmitted field. In accordance with the 35 present invention, this particular attribute can be utilized to increase the capacity of existing channels.
More particularly, the present invention effectively creates a multiplexed channel by transmitting new fields in the 4Q time slots which would normally contain a repeated field in this example. FIG. 2A illustrates a video image sequence wherein fields 3 and 8 are replaced with interactive fields II and 12 rather than being repeated fields of the movie. At the
user's end, when it is desired to view the movie, the „.
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interactive fields II and 12 are removed from the video signal and the appropriate previously sent field of the video signal is repeated. FIG. 2B illustrates a reconstructed video image sequence, at the users end, which corresponds to a full motion video movie sequence. Interactive fields II and 12 5Q have been effectively replaced by the repetition of fields Ml-1 and M3-1 and Ml-3 and M3-3 respectively, at the user's end. This process reproduces the desired video image sequence with no loss of quality. (In the case where the repeated field is the second field of the image, there will be 5J a slight loss of vertical resolution on the repeated field).
Alternatively, if the user desires to access the interactive service, only the fields II and/or 12 is selectively retrieved from the video signal for display on the viewer's receiver. Each retrieved interactive field is continuously displayed on 60 the viewer's receiver at the standard television frame rate, to provide a still frame, until the next interactive field of the presentation is received.
It can therefore be appreciated that in the example described above, the present invention effectively doubles 65 the capacity of a single channel to include the concurrent transmission of, for example, 24 image frames (48 fields)
6
per second which can be utilized for the distribution of a movie, and 12 image fields per second which can be used for an interactive service. Reduced vertical resolution can be alleviated by the terminal with vertical interpolation stored lines of the first field to generate the second field of a frame.
Referring now to FIG. 3, an overall system diagram of a television system combining broadcast and interactive television services is illustrated. When an interactive presentation is requested, according to the present invention, the viewer sends instructions to a presentation system 10 at a central location to identify one or more presentations that are desired to be viewed. These instructions are transmitted from the viewer's remote location to the central location by means of a wire, fibre optics, cellular, radio or other telephone network 12. For example, the instructions might be transmitted as touch tones which the user generates by depressing buttons of the keypad on his telephone set. More preferably, however, the instructions are generated within a user terminal 14 located at the viewer's home, and transmitted over the telephone network as DTMF or modem tones on an analog line, or data on a digital line such as the ISDN format. For ease of use, the terminal 14 is preferably controlled by means of a remote control unit 16 which transmits instructions to the terminal 14 via infrared signals.
The presentation system 10 processes the incoming requests from the viewers and retrieves video images and accompanying audio associated with the presentations desired by the various viewers. In one embodiment of the invention, each image is labelled with a corresponding identification. For example, the identification might indicate the particular video presentation to which it pertains, or it may be an address identifying the viewer for whom it is intended. All of the selected video images are assembled into a video signal that is transmitted to the viewers.
The presentation system 10 basically comprises three main subsystems, an audio subsystem 18, a video subsystem 20 and system controller 22. The servicing of the incoming requests received by the audio subsystem and assembly of requested images into a video signal by the three subsystems is carried out under the management of the system controller 22. Once the various requested images have been assembled into a video signal, this signal is transmitted over a suitable transmission medium 24, such as a CATV system, a terrestrial or satellite broadcast network, or a fibre optic network.
In operation, the terminal 14 selectively stores video images and continuously displays them on to the television set 36. When a viewer activates the terminal 14 to view an interactive presentation, the user terminal 14 is tuned to a television channel associated with the interactive presentation images, e.g. channel 33. The terminal has a code relating to the identification label in the images pertaining to the interactive presentation the viewer desires to see. The user terminal examines the images transmitted over the appropriate channel for those which are labelled with the proper identification, and stores each such image, one at a time, in a memory (not shown). The stored image is continually retransmitted from the terminal 14 to the viewer's television receiver 36 for display as a still image. When the next image in a desired video presentation reaches the user terminal, it replaces the preceding image in the memory and is then displayed.
The presentation system 10 is also operable in a noninteractive display mode. The terminal will store and retransmit only the broadcast video images to the television set 36 in accordance with the process discussed with reference to FIGS. 2A and 2B. When the terminal is operating in
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