Method and apparatus for encoding a video signal having multi-language capabilities

What is claimed is:

1. An audio-video system for encoding and decoding a video signal and a plurality of corresponding audio signals into a standard audio-video format, said format comprising a video signal and at least one full bandwidth audio signal, comprising:

encoder means for receiving an input video signal, a first input audio signal, and a plurality of second input audio signals corresponding to said input video signal, said encoder means generating signals in the standard audio-video format signal by combining said input video signal and said plurality of second input audio signals by replacing selected portions of said input video signal with said plurality of said second input audio signals to produce an encoded video signal, said first input audio signal output as the at least one full bandwidth audio signal, said encoder means outputting said first input audio signal and said encoded video signal in the standard audio-video format;

audio-video signal communication means for receiving in the standard audio-video format, said first input audio signal and said encoded video signal from said encoder means, said communication means outputting said first input audio signal and said encoded video signal in a predetermined manner; and

decoder means coupled to said signal communication means for receiving said encoded video signal and said first input audio signal, said decoder means comprising;

means for separating said plurality of second input audio signals from said encoded video signal so as to form an unencoded video output signal and a plurality of second audio signals; and

combining each of said plurality of second audio signals with the first input audio signal so as to form a plurality of combined audio signals, said decoder means outputting said unencoded video output signal and said plurality of combined audio signals.

2. The system of claim 1, further comprising a signal delivery means coupled to said decoder means, said signal delivery means including a selection means such that at least one of said plurality of said combined audio signals may be played with said unencoded video output signal.

3. The system of claim 1 wherein said input video signal represents a video picture made up of a plurality of horizontal scan lines and said selected portions of said input video signal correspond to a predetermined number of said scan lines.

4. The system of claim 3 wherein said scan lines are located at a top portion of said video picture.

5. The system of claim 3 wherein said predetermined number of scan lines are equal to the number of said second input audio signals.

6. The system of claim 5 wherein said portion of said video signal corresponding to a selected scan line exclusively stores information from one of said second input audio signals.

7. The system of claim 1 wherein said first input audio signal is a high bandwidth signal, and said plurality of second input audio signals are low bandwidth signals.

8. The system of claim 1 wherein said encoder means comprises:

input means for receiving said input video signal and said plurality of second input audio signals;

synchronization means responsive to said input video signal for sensing timing signals contained in said input video signal;

audio signal linking means responsive to said plurality of second input audio signals for converting said plurality of second input audio signals into a stream of information;

data storage means operatively coupled to said audio signal linking means for storing said stream of information;

timing means responsive to said synchronization means and in communication with said storage means, said timing means triggering a release of said stream of information from said storage means in discrete bursts of data responsive to said synchronization means; and

video signal combining means coupled to said input means and said data storage means for combining said bursts of data into said input video signal in a predetermined manner so as to form said encoded video signal, said combining means then outputting said encoded video signal.

9. The system of claim 8 wherein said audio signal linking means comprises a time division multiplexer.

10. The video system of claim 9 wherein said audio signal linking means further comprises an analog-to-digital converter for converting said stream of information from the analog domain to the digital domain.

11. The system of claim 10 further comprising a digital-to-analog converter coupled between said data storage means and said video signal combining means for converting said bursts of data from the digital domain to the analog domain.

12. The system of claim 1 wherein said signal communication means further includes data storage means for storing said encoded video signal.

13. The system of claim 1 wherein said audio-video signal communication means comprises a video cassette player.

14. The system of claim 1 wherein said audio-video signal communication means comprises a satellite communication system.

15. The system of claim 1 wherein said audio-video signal communication means comprises a video disk player.

16. The system of claim 1 wherein said decoder means comprises:

input means for receiving said encoded video signal and said first input audio signal, said encoded video signal having segments with said plurality of second input audio signals encoded thereon;

timing means responsive to said encoded video signal for identifying said segments of said encoded video signal containing said plurality of second input audio signals;

memory means coupled to said timing means and said input means for storing said segments of said encoded video signal containing said plurality of second input audio signals;

audio signal separating means coupled to said memory means and responsive to said timing means for separating said plurality of second input audio signals from the encoded video signal;

audio signal combining means coupled to said audio signal separating means and said input means for receiving said separated audio signals and said first input audio signal, said audio signal combining means combining a reproduction of said first input audio signal with each of said plurality of separated audio signals; and

output means for outputting said video signal and said plurality of combined audio signals.

17. The system of claim 15 further comprising line blanking means coupled to said timing means for recording a null signal over said storage segments of said restored video signal prior to outputting said restored video signal.

18. The system of claim 15 wherein said audio signal separating means comprises a demultiplexer.

19. The system of claim 15 wherein said timing means includes a phase-locked loop.

20. A device for decoding an encoded video signal having segments with a plurality of audio signals encoded thereon, and a corresponding full bandwidth audio signal, each of said plurality of audio signals comprising voice audio corresponding to the video signal, said encoded video signal in a standard audio-video format, said format comprising a video signal and at least one full bandwidth audio signal, said device comprising:

input means for receiving said encoded video signal and at least one full bandwidth audio signal, said full bandwidth audio signal comprising music and effects corresponding to the video signal;

timing means responsive to said encoded video signal for identifying said segments of said video signal containing said plurality of audio signals;

memory means coupled to said timing means and said input means for storing said segments of said encoded signal containing said plurality of audio signals;

audio signal separating means coupled to said memory means and responsive to said timing means for separating said plurality of audio signals from said encoded video signal so as to form an unencoded video signal;

audio signal combining means coupled to said audio signal separating means and said input means for receiving said separated audio signals and said full bandwidth audio signal, said combining means combining said music and effects audio signal with each of said voice audio signals; and

output means for outputting said unencoded video signal and said plurality of combined audio signals.

21. An audio-video system for encoding and decoding a video signal and a plurality of corresponding audio signals, said video signal representing a video picture made up of a plurality of horizontal scan lines, said system comprising:

encoder means comprising;

means for receiving an input video signal, a first audio signal, and a plurality of second audio signals corresponding to said input video signal,

means for replacing portions of said input video signal which correspond to preselected scan lines of said video picture with said plurality of second audio signals so as to form an encoded video signal; means for outputting said encoded video signal and first audio signal in a standard audio-video format comprising a video signal and at least full bandwidth audio signal;

audio-video signal communication means for receiving said first audio signal and said encoded video signal from said encoder means in said standard audio-video format, said communication means outputting said first audio signal and said encoded video signal in a predetermined manner, said signal communication means further including a data storage means for storing said encoded video signal; and

decoder means coupled to said signal communication means comprising;

means for receiving said encoded video signal and said first audio signal,

means for separating said plurality of second audio signals from said encoded video signal so as to form a decoded video signal and plurality of second audio signals, and

combining each of said plurality of second audio signals with said first audio signal so to a form a plurality of combined audio signals, said decoder means outputting said unencoded video signal and said plurality of combined audio signals; and

a signal delivery means coupled to said decoder means, said delivery means including a selection means such that at least one of said plurality of said combined audio signals may be played with said decoded video signal.

22. The system of claim 21 wherein said first audio signal corresponds to the music and effects portion of a complete audio signal and wherein said plurality of second audio signals correspond to a plurality of sets of voices in different languages, such that each set of voices in each of said languages may be combined with music and effects signal to form said complete audio signal.

23. A method for decoding an encoded video signal having intervals with a plurality of audio signals representing voice audio in different languages corresponding to the video signal encoded thereon, said encoded video signal in a standard audio-video format comprising a video signal and at least one full bandwidth audio signal, said method comprising the steps of:

receiving a said encoded video signal and a full bandwidth audio signal comprising a music and effects audio signal corresponding to the video signal;

locating said intervals of the video signal containing the plurality of audio signals;

writing said intervals to a memory storage device in bursts corresponding to said intervals of the video signal;

removing said audio signals from said video signal so as to form an unencoded video signal;

passing said stored audio signals through a demultiplexer to an audio signal combining device;

inputting said music and effects audio signal to the audio signal combining device;

combining said music and effects audio signal with each of said plurality of audio signals to form a plurality of combined audio signals comprising music and effects and voice audio in different languages corresponding to the video signal;

transmitting said unencoded video signal and combined plurality of audio signals to a predetermined destination.

24. An audio-video system for encoding and decoding a video signal and a plurality of corresponding audio signals into a standard audio-video format, said format comprising a video signal and at least one full bandwidth audio signal, comprising:

encoder means for receiving an input video signal, a first input audio signal, and a plurality of second input audio signals corresponding to said input video signal, said encoder means generating signals in the standard audio-video format signal by combining said input video signal and said plurality of second input audio signals by replacing selected portions of said input video signal with said plurality of said second input audio signals to produce an encoded video signal, said first input audio signal output as the at least one full bandwidth audio signal, said encoder means outputting said first input audio signal and said encoded video signal in the standard audio-video format;

audio-video signal communication means for receiving in the standard audio-video format, said first input audio signal and said encoded video signal from said encoder means, said communication means outputting said first input audio signal and said encoded video signal in a predetermined manner; and

decoder means coupled to said signal communication means for receiving said encoded video signal and said first input audio signal, said decoder means comprising;

means for separating at least one of said plurality of second input audio signals from said encoded video signal so as to form an unencoded video output signal and at least one of the plurality of second audio signals; and

combining each of at least one of the plurality of second audio signals with the first input audio signal so as to form at least one combined audio signal corresponding to the unencoded video signal, said decoder means outputting said unencoded video output signal and at least one combined audio signal.

25. The system of claim 24 wherein said encoder means comprises:

input means for receiving said input video signal and said plurality of second input audio signals;

synchronization means responsive to said input video signal for sensing timing signals contained in said input video signal;

audio signal linking means responsive to said plurality of second input audio signals for converting said plurality of audio signals into a stream of information;

data storage means operatively coupled to said audio signal linking means for storing said stream of information;

timing means responsive to said synchronization means and in communication with said storage means, said timing means triggering a release of said stream of information from said storage means in discrete bursts of data responsive to said synchronization means; and

video signal combining means coupled to said input means and said data storage means for combining said bursts of data into said input video signal in a predetermined manner so as to form said encoded video signal, said combining means then outputting said encoded video signal.

26. The system of claim 24 wherein said decoder means comprises:

input means for receiving said encoded video signal and said first input audio signal, said encoded video signal having segments with said plurality of second input audio signals encoded thereon;

timing means responsive to said encoded video signal for identifying said segments of said encoded video signal containing said plurality of second input audio signals;

memory means coupled to said timing means and said input means for storing said segments of said encoded video signal containing said plurality of second input audio signals;

audio signal separating means coupled to said memory means and responsive to said timing means selection means for separating at least one of the second input audio signals from the encoded video signal;

audio signal combining means coupled to said audio signal separating means and said input means for receiving said separated audio signals and said first input audio signal, said audio signal combining means combining the first input audio signal with each of said separated audio signals; and

output means for outputting said video signal and said the combined audio signals.

27. A device for decoding an encoded video signal having segments with a plurality of audio signals encoded thereon, and a corresponding full bandwidth audio signal, said plurality of audio signals comprising voices corresponding to the video signal, said encoded video signal in a standard audio-video format, said format comprising a video signal and at least one full bandwidth audio signal, said device comprising:

input means for receiving said encoded video signal and at least one full bandwidth audio signal, said full bandwidth audio signal comprising music and effects corresponding to the video signal;

timing means responsive to said encoded video signal for identifying said segments of said video signal containing said plurality of audio signals;

memory means coupled to said timing means and said input means for storing said segments of said encoded signal containing said plurality of audio signals;

audio signal separating means coupled to said memory means and responsive to said timing means for separating at least one of the audio signals from said encoded video signal so as to form an unencoded video signal;

audio signal combining means coupled to said audio signal separating means and said input means for receiving said separated audio signals and said full bandwidth audio signal, said combining means combining said full bandwidth audio signal and each of the separated audio signals such that the music and effects audio signal is combined with each of the separated voice audio signals; and

output means for outputting said unencoded video signal and the combined audio signals.

28. A method for decoding an encoded video signal having intervals with a plurality of audio signals representing voice audio in different languages corresponding to the video signal encoded thereon, said encoded video signal in a standard audio-video format comprising a video signal and at least one full bandwidth audio signal, said method comprising the steps of:

receiving a said encoded video signal and a full bandwidth audio signal comprising a music and effects audio signal corresponding to the video signal;

locating said intervals of the video signal containing the plurality of audio signals;

writing the intervals of at least one of the voice audio signals to a memory storage device in bursts corresponding to said intervals of the video signal;

removing said audio signals from said video signal so as to form an unencoded video signal;

passing said stored audio signals through a demultiplexer to an audio signal combining device;

inputting said music and effects audio signal to the audio signal combining device;

combining said music and effects audio signal with each audio signal to form at least one combined audio signals comprising music and effects and voice audio in a predetermined language corresponding to the video signal;

transmitting said unencoded video signal and combined audio signals to a predetermined destination.

Description Submit all comments and votes

FIELD OF THE INVENTION

The present invention relates to the field of video signals and more particularly to a method and apparatus for encoding and decoding a video signal having multi-language capabilities.

BACKGROUND OF THE INVENTION

In places where multiple languages are spoken, there is a need to provide movies, prerecorded television programs, educational videos as well as many other forms of video/audio programing in multiple languages to accommodate the multi-lingual viewing audience. Most often it desired to have the capability to play back the multiple languages simultaneously with a single video signal. One technique used to achieve this result is to use different viewing channels for the different channels. A separate prerecorded video tape is generated for each language. Each tape contains the same video information but necessarily has a different audio signal for each desired language. The tapes are individually played and broadcasted on different channels The viewer selects the channel according to the language he wishes to hear. This method is quite obviously inefficient as it requires a number of video playback means and available television channels or frequencies equal to the number of languages in question.

Briggs, U.S. patent application Ser. No. 07/411,214 entitled Multi-Language Recording and Reproducing System describes a multiple language system wherein a plurality of audio tracks, each representing a different language, are encoded into the video signal using frequency modulation techniques. However, that method is disadvantageous because it employs analog techniques which compromise video quality and produce an encoded signal incompatible or marginally compatible with several classes of important communications channels.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide a video system in which multiple languages can be encoded within the bandwidth of a standard video signal.

It is another object of the present invention to provide a multiple language system that can operate in conjunction with existing videotape formats and existing videotape players without modification of either the format or the player.

It is another object of the present invention to provide a multiple language broadcast system which provides a selectable multi-lingual capability without modification of the bandwidth of the broadcast signal.

It is further an object of the present invention to provide a multiple language broadcast system which provides selectable multi-lingual capability with little or no degradation in video quality or sound quality.

An audio/video system for encoding and decoding a video signal and a plurality of corresponding audio signals is disclosed. The system includes an encoder means for receiving an input video signal, a first audio signal, and a plurality of second audio signals which correspond to the input video signal. The encoder means combines the input video signal and the plurality of second audio signals to produce an encoded video signal but leaves the first audio signal substantially unchanged and then outputs the first audio signal and the encoded video signal. An audio/video signal communication means is connected to the encoder. The audio/video signal communication means accepts the encoded video signal and the first audio signal and transmits them to a decoder. The decoder is coupled to the signal communication means and accepts the encoded video signal and the first audio signal. The decoder means then separates the plurality of second audio signals from the encoded video signal leaving an unencoded video signal. The decoder then combines each of the plurality of second audio signals with a reproduction of the first audio signal so as to form a plurality of combined audio signals. The decoder then outputs the unencoded video signal and the plurality of combined audio signals. A signal delivery means which is coupled to the decoder includes a selection means. Selection means allows at least one of the plurality of the combined audio signals to be played with the unencoded video signal in a manner determined by the user.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of the components of the present system, showing their respective input/output signals.

FIG. 2 is a block diagram of the encoder element of the present invention.

FIG. 3 is a block diagram of the decoder element of the present invention.

FIG. 4 is a block diagram of the preferred embodiment of the delivery system of the present invention in conjunction with the decoder element.

FIG. 5 is a block diagram of an alternative embodiment of the delivery system.

DETAILED DESCRIPTION OF THE INVENTION

An audio/video system with multi-language capability for encoding a video signal is described. In the following description, numerous details such as sampling rates and signal levels are set forth in order to provide a better understanding of the present invention. It will be apparent to those skilled in the art that the invention may be practiced without these specific details. In other instances, well known components such as the phase locked loop circuit are shown in block form so as not to obscure the present invention unnecessarily.

In order to better understand the operation of the present invention, it is helpful to briefly describe the manner in which a video signal is reproduced on a video monitor. The composition of the video signal is governed by industry standards--e.g., those established by the National Television System Committee. ("NTSC"). Under the NTSC standard, the video screen is divided up into 2621/2 separate horizontal lines of picture elements. The electron beam which is used to actually generate the picture by exciting the picture elements which causes the picture elements to be illuminated at a predetermined intensity scans the lines in a left to right, top to bottom fashion. As the electron beam moves across the video screen it is modulated in intensity so as to modulate the intensity of the picture elements and produce the video picture that is visible to the user.

Timing pulses are embedded within the NTSC video signal to control the operation of the electron beam. This is best explained by an example. Assume that the electron beam is horizontally scanning across one of the 525 lines on the video monitor. Just as the beam reaches the right edge of the screen, a timing pulse in the video signal will indicate to the beam that it is to stop scanning. This timing pulse is known as a "horizontal retrace" pulse. The beam will briefly turn off and execute a horizontal retrace function. During this function, the electron beam will drop down to the next lower scan line and return to the left side of the video screen. After the horizontal retrace, the beam will turn back on and re-commence scanning. This process repeats until all 2621/2 lines of the video screen have been scanned by the electron beam. When the complete screen has been scanned, a "vertical retrace" timing pulse is inserted into the video signal. The electron beam is again briefly turned off and executes a vertical retrace function, when it returns to the beginning point at the top scan line of the video screen. In this manner, the entire screen is continuously updated so as to form the entire video picture.

This discussion is not intended as a complete description of the operation of the video monitor. Instead, it is included only to the extent that it assists in the understanding of the structure and operation of the present invention. Also, the present invention is not limited to use with the NTSC standard for the composition of video signals. It will be apparent to those skilled in the art that the techniques of the present invention may be adapted for use with any sequential video format. These may include the formats which are known in the art as PAL, SECAM, EMAC and the like. In any event, the video monitor is not an element of the present invention. The invention consists of the system for encoding a video signal as described.

Referring first to FIG. 1, a block diagram of the preferred embodiment of the major components of the present invention and their corresponding input and output signals is shown. The system includes an encoder element 10 which accepts a standard NTSC compatible signal. Any NTSC compatible signal has two components--the video portion and the audio portion. The encoder element 10 therefore accepts an input video signal 13, as well as a first audio signal which is termed herein the as the "music and effects" signal 14. The standard NTSC signal provides two dedicated, high bandwidth, channels for audio information. These two channels typically correspond to the left and right stereo channels of the complete audio signal. The stereo channels are usually timed to be in synchronization with the video portion of the NTSC signal. In this description, these two channels collectively make up the music and effects signal 14.

It has been found that the language portion of any given audio signal does not occupy a large bandwidth. For example, a complete audio signal will typically occupy a signal range from 0-20,000 Hz. However, the language portion will usually occupy only a 4 kHz portion of that total signal bandwidth. The rest of the bandwidth is occupied by other sounds such as music, background noises, and the like.

As noted above, the language portion of the audio signal has a relatively narrow bandwidth. The audio/video system of the present invention takes advantage of the narrow bandwidth of the language portion of the audio signal to combine the audio information on the auxiliary language tracks 15 with the video signal. The music and effects channel 14 contains all of the remaining audio information that would normally accompany the video signal.

The language portion of the audio signal is input through the auxiliary audio channels 15. In the preferred embodiment there are twelve such channels. In the preferred embodiment, these signals correspond to the left and right stereo channels of complete audio signal for six different languages. While the preferred embodiment inputs multiple language tracks in stereo through the auxiliary channels 15, it will be understood by those skilled in the art that other information can be provided through these channels without departing from the overall scope of the present invention. For example, there may be twelve monaural language signals or some combination of stereo and monaural signals. Alternatively, the auxiliary channels may be used to transmit other types of information through the video format of the present invention. All of the auxiliary audio channels in the preferred embodiment are timed to be in synchronization with the video portion of the NTSC signal. It will be apparent to those skilled in the art that this synchronization is not required. Depending on the type of information which is being transmitted, the synchronization may or may not be desirable. In the preferred embodiment, the synchronization is accomplished by ensuring that the input video signal and the auxiliary channels are in synchronization as they are being input to the encoder. It will be apparent to those skilled in the art that various time delay features could be built into the encoder so that the input signals do not need to be in exact synchronization when they are input. The nature and structure of these time delay features will be apparent to those skilled in the art from reading the following description of the encoder element.

The encoder element 10 combines the input video signal 13 with the auxiliary audio channels to form an encoded video signal 16 which is NTSC compatible. (For commercial reasons it is desirable that all video signals be compatible with a particular standard. This allows the signal to be used in conjunction with existing video equipment. A standardized signal obviates the need to purchase specialized equipment.) The combination of the audio and video signals is accomplished by "overwriting" the language tracks from the auxiliary channels 15 onto preselected portions of the input video signal 13. The music and effects audio signal 14 is simply passed through the encoder element 10 without any substantial change. All of the signals are then output by the encoder element 10. The structure and operation of the encoder element 10 is described in more detail below with respect to FIG. 2.

The output of the encoder element 10 is passed to an audio video signal communication means 11 as shown in FIG. 1. The function of the signal communication means 11 is to transfer the encoded video signal 16 and the music and effects audio signal 14 from the encoder element 10 to the decoder element 12. Additionally, the signal communication means may store the signals for use at a later time. In the preferred embodiment, the signal communication means 11 is a standard video cassette recorder ("VCR"). The VCR allows the output of the encoder element 10 to be recorded for playback at any desired time. It will be apparent to those skilled in the art, however, that many other devices can be used with equivalent results. For example, the signal communication means may simply comprise a fiber optic transmission cable or microwave transmitter for transmitting the signals in real time to a distant location. Alternatively, the content of the audio and video signals may be digitized and stored in a binary computer memory for reproduction at a later date. These and other equivalent means may be substituted for the VCR, as will be apparent to those skilled in the art.

Referring again to FIG. 1, the present invention also includes a decoder element 12. The function of the decoder element is to transform the encoded video signal 16 into a signal which allows the information contained on any or all of the auxiliary audio channels 15 to be played in conjunction with the input video signal 13. As noted above, the decoder element 12 accepts the audio and video signals from the signal communication means 11. The decoder element 12 then removes the language tracks from the encoded video signal 16. The decoder element 12 duplicates the music and effects signal 14. Each of the language tracks are combined with a reproduction of the music and effects signal 14 so as to form a number of composite audio signals 18. These combined audio signals 18 are high bandwidth signals. They are output by the decoder element for eventual use by a user. The structure and operation of the decoder element is described in more detail below with respect to FIG. 3.

Referring next to FIG. 2, a block diagram of the encoder element 10 is shown. As discussed above, the encoder element 10 accepts three separate groups of input signals. These are the input video signal 13, the auxiliary audio channels 15, and the music and effects channel 14. As shown in FIG. 2, the music and effects signal is passed through the encoder without any substantial change. The video signal 13 is divided into two components. The first component passes through amplifier 31. The second component enters element 32. Element 32 is termed a synchronization stripper in the preferred embodiment because it separates the synchronization (timing) pulses from the video signal. These timing signals are used to direct the horizontal and vertical retrace functions of the electron beam as was described above. The output of the synchronization stripper 32 is used to generate a system clock 40 for the encoder element 10. The system clock is made up of the phase locked loop 33 ("PLL") and the voltage controlled oscillator 34 ("VCO"). The operation of the PLO/VCO combination is well-known to those skilled in the art and the operation of the clock 40 will therefore not be described in detail herein. It is only necessary that the clock generate a series of timing pulses at a desired frequency rate. The output of the synchronization stripper 32 is transferred via signal line 41 to the timing logic and address generator means 35. The output of the clock 40 is also applied to the timing means 35 over signal line 42. The timing logic and address generator means 35 uses these two signals to control the operation of the digital memory 39 as will be described more fully below.

The timing logic and address generator means 35 controls the overall operation of the encoder 10. It is chosen from any one of a number of suitable devices which have the capability to control the operation of several digital components simultaneously. In the preferred embodiment, the timing logic means 35 is a custom made programmable gate array ("PGA"). The PGA is chosen for the preferred embodiment because it allows high speed operation with a low manufacturing cost. It will be apparent to those skilled in the art that other, equivalent, devices can be used with equal effectiveness. For example, a digital microcomputer could replace the PGA and still effectively control the encoder 12.

The auxiliary audio channels 15 are input in a parallel fashion to the multiplexer 37. The multiplexer 37 is essentially a digital switch. It uses time division multiplexing techniques in order to sequentially sample each of the auxiliary audio channels. It is well known to those skilled in the art that a minimum sampling rate will allow each of the auxiliary audio channels to be multiplexed onto a single line without the loss of any of the information contained therein. This minimum sampling rate is known as the "Nyquist" rate. For any given analog signal the Nyquist rate is equal to twice the bandwidth of the signal. As noted above, the auxiliary audio channels will--in the preferred embodiment--contain language information. These signals typically have a bandwidth of approximately 4 kHz. Therefore, the Nyquist sampling rate for these signals is 8 kHz. It has been found that the construction of filters and other electric components is simplified when the sampling frequency of the signal which is being processed is increased. Therefore, in the preferred embodiment of the present invention, the auxiliary audio channels 15 are sampled by the multiplexer 37 at a frequency rate of 15.75 kHz. It will be apparent to those skilled in the art that this particular frequency is an arbitrary design choice and that other frequencies can be used with equal effectiveness. The timing details of the sampling rate are controlled by appropriate clock pulses generated by the timing logic and address generator means 35.

After the audio channels are sampled, they are converted to a digital format by the analog to digital converter 43. This type of analog to digital converter is well known to those skilled in the art and will not be described in detail herein.

The output of the analog to digital converter 43 is transferred over signal line 44 and stored in digital memory 39. Digital memory 39 is partitioned into a number of sections. (Those partitions are not necessarily physical in nature, but instead refer to the fact that the memory stores several discrete groups of data.) The number of partitions is equal to the number of auxiliary audio channels 15 which are input into the encoder 10. Thus, in the preferred embodiment of the invention, there are 12 separate partitions of the memory 39. The input stream from each auxiliary audio channel is sequentially stored within its corresponding partition of the memory 39. The timing logic and address generator means 35 generates an address signal over address lines 45 which instructs the memory where to store each bit of information from analog to digital converter 43. Timing is controlled by the timing signals generated by the system clock 40 over signal line 42. It is the information in memory 39 which is combined with the input video signal 13 so as to form the encoded video signal 16.

The present invention encodes the audio information onto the video signal by selecting a portion of the video signal which corresponds to certain scan lines on the video display and replacing the existing video information with desired audio information. In this description, when information is described as being written onto (or read from) a given scan line, it is to be understood that the audio is being combined with (or being removed form) that portion of the video component of the signal formal which corresponds to the particular scan line in question. The information is not actually "written onto" a scan line; it is simply inserted into the video signal at the proper time.

In the preferred embodiment of the invention, a preselected number of scan lines located at the top portion of the video pictures are used to store audio information. These specific lines are chosen for a variety of reasons. Most importantly, when the video signal is displayed, these lines cannot be seen by a user. Thus, there will be no loss of picture quality and the user will not notice that the audio information has been encoded onto the video signal. Of course, any of the other scan lines can be used to store the audio information. In particular, the bottom scan lines can be used because they too are not seen by the user when the picture is displayed.

In the preferred embodiment of the invention, one entire scan line is dedicated to each separate auxiliary audio channel. Thus, in the preferred embodiment of the invention, the portion of the video signal corresponding to the top 12 lines of the video picture are encoded with audio information.

The operation of the actual encoding process is as follows. After the electron beam executes a vertical retrace it will begin to scan the first line of the video signal. The synchronization stripper 32 separates the vertical retrace signal from the overall video component and transmits it to the timing logic means 35 over signal line 41. The timing means 35 will recognize the vertical retrace signal and instruct the memory 39 to output the desired information for the first auxiliary audio channel. To do so, it sends a signal over read/write line 46 instructing the memory to write data, and transmits the proper address for the initial location in the first partition of the memory over address line 45. Memory 39 then outputs (in proper sequential format) the information which had been previously stored for a first auxiliary audio channel.

The digital information from memory 39 is transmitted to digital to analog converter 38 where it