WO1999040722A1

WO1999040722A1 - Method and apparatus for record and playback processing of television auxiliary data signals

Info

Publication number: WO1999040722A1
Application number: PCT/GB1999/000387
Authority: WO
Inventors: Kenneth Austin
Original assignee: Danmere Limited
Priority date: 1998-02-05
Filing date: 1999-02-05
Publication date: 1999-08-12
Also published as: AU2529399A; GB9802414D0

Abstract

Signal processing apparatus comprising means operating on an input comprising data signals transmitted via or through terrestrial, cable or satellite television networks and generating an output in a form suitable for storage onto magnetic video tape. The apparatus comprising error correction means to reduce stored errors. Programming means is provided to provide an adjustable storage rate. A method of recording such a signal on magnetic storage after decoding and error coding is also described.

Description

METHOD AND APPARATUS FOR RECORD AND PLAYBACK PROCESSING OF TELEVISION AUXILIARY DATA SIGNALS

DESCRIPTION

The present invention relates to the processing and storage of television signals, and in particular to the processing of such signals to facilitate recordal and/or retrieval of audio visual and data signals using a Video Cassette Recorder. Many modern television receivers are adapted to receive data transmitted alongside the standard television picture. In the United

Kingdom the system is known as Ceefax and Oracle. Data is transmitted on the first few lines of picture corresponding to the Vertical Blanking Interval (VBI). As these lines are not normally displayed on a television set, the data does not interfere with the normally received picture.

In the United States of America the data signals convey information which is related to the picture that is being transmitted, such as video clips, music, internet links, games or software. Data transmitted in this manner is modulated in a form suitable for transmission over normal television systems such as terrestrial, cable or satellite television systems.

When these transmissions are recorded onto domestic videotape the data signals are lost as the VCR does not have sufficient bandwidth to record the data in its original form. The

video recorder also introduces errors associated with the signal processing characteristics of the VCR, such as the dropout compensation circuitry and the picture edge enhancement circuitry Accordingly, it is not currently possible to use a VCR to record on domestic video tape such transmissions including the transmitted data so that either can be retrieved at a later date. 2

Similarly it is not possible to recover data recorded on video tape using an existing VCR.

Television based data retrieval systems are known, but suffer from a lack of local high capacity data storage and from the fact that analog and digital information cannot be stored on the same media.

It is an aim of the present invention to provide a solution.

Accordingly, one aspect of the invention provides signal processing apparatus comprising converter means operating on an input comprising data signals transmitted via or through terrestrial, cable or satellite television networks and generating an output in a form suitable for storage onto magnetic storage tape.

More particularly said converter means operates on data transmitted in the Vertical Blanking Interval and converts it into a form suitable for recording, thereby enabling any data and any analogue picture component where present, to be recorded on the magnetic storage tape. The preferred magnetic storage tape is a video cassette. Said signal processing apparatus operates to provide the signals to be recorded onto a Video Cassette Recorder (VCR). Preferably said signal processing apparatus incorporates programmable means to provide an adjustable storage rate. It is also preferred to provide programmable means to provide one of a plurality of selectable modulation techniques. Such means facilitate operation with different data formats and video recorder characteristics.

The signal processing apparatus comprises an error correction means which operates on

the data to render it suitable for recording onto the storage tape. The error correction means is operable to reduce stored errors rather than errors associated with data transmission. 3

Conveniently the signal processing means further comprises means which acts to adjust the number and/or the position of lines used for encoded digital data. The number of lines may be set to cover up to the entire number of visible lines in a picture frame. Associated means may be provided for blanking the video signal where data would otherwise be visible in the video frame, or for providing a graphical substitute such as a banner, menu or computer type icons.

The apparatus may be provided with additional input provisions whereby data from

other sources, such as via a modem or other data link, may be processed for recording on said magnetic storage tape.

The preferred signal processing apparatus also comprises means for decoding data signals recorded onto magnetic storage tape into a format suitable for viewing on television. The decoding provisions correspond to the encoding provisions.

Another aspect of the invention provides a method of recording on magnetic storage tape a signal transmitted via or through a terrestrial, cable or satellite television network incorporating a data signal, comprising isolating the data signal and converting the recovered data into a form suitable for storage onto said magnetic storage tape.

More particularly the method comprises operating on the signal recovered from a tuner

to extract data from the Vertical Blanking Interval using a Vertical Blanking Interval decoder and passing the signal from the VBI decoder to an error coder that adds redundancy to the data for performing an error detection and correction operation. The method further comprises passing the data encoded with redundancy to a shuffle memory which transposes bits over 4

several lines or frames to spread burst errors. The method further comprises passing the encoded data to a coder, preferably one of a number of coders, where the data rate and the number of bits per pixel is assigned.

The method further comprises converting the data to an analogue signal using a digital

to analogue converter, and the resulting signal is added to a carrier reference and line and frame reference signals. This signal is then mixed with analog picture signal to form a combined data and picture signal. For a combined signal the data portion may be restricted to a small number of the video lines - such as those in the vertical blanking interval. Where higher data storage is

required or where the video recorder to be employed can only handle a slower data rate, the number of lines assigned for data storage is increased. Data lines which extend into the visible portion of the video frame may be blanked out when the data is recovered. If no picture component is required the whole of the video frame is available for data storage. This provides a means of storing entire digital frames of data on the same tape as the analogue video component. This facilitates the storage and retrieval of for example content related data down

loaded from the internet or other sources of such information - (say at the end of a recorded television programme) as well as the recovery of data from pre-recorded video cassettes available to buy, rent or hire.

The present invention will now be described further, hereinafter, by way of example

only, with reference to the accompanying drawings; in which:-

Figure 1 illustrates in block diagram form signal processing apparatus according to the present invention, 5

Figure 2a illustrates one embodiment of programmable data encoder, Figure 2b illustrates one embodiment of programmable data decoder, Figure 3, 4 and 5 illustrate diagrammatically various error correction schemes, Figure 6 illustrates schematically the composition of a one line video signal, and Figure 7 illustrates by way of example various encoded and recovered signals.

In a known set top device, television signals are processed by a tuner T to separate data located in the vertical blanking interval from the picture signal. The picture signals are processed by a video system 1 and passed to the television 2. The data signals are processed by a CPU and held in memory M until they are required to be routed through the video system to the television for viewing. The transmitting of the picture signals or the recovered data signals

to the television monitor is under the control of the user and is usually controlled by an infrared controller IR which communicates with the CPU. Such a system is similar to boxes A and B in Figure 1 but the output from the video system would be routed directly to the television and there would be no data or control line X between the CPU and the box C. A video cassette recorder (VCR) is disposed signal flowwise between the television and the processing apparatus which receives signals from the terrestrial, cable or satellite networks. The infra-red controller for the set top box is advantageously used for controlling the VCR.

Data signals are recovered and processed as described below with reference to Figure 2a to facilitate recording onto magnetic storage tape.

Firstly, television signals recovered from a tuner T are passed to the Vertical Blanking

Interval decoder (VBI). Data from the VBI decoder is passed to an error coder that adds 6

redundancy to the data, so as to enable error detection and correction of the recovered signal. Two methods are used, Cyclic Redundancy Checks (CRC) and Reed Solomon coding. These techniques are well known in the art and are not described in further detail. Other schemes could be employed as will be apparent to those skilled in the art. The data encoded with redundancy is now passed to the shuffle memory SM, which transposes bits over several lines or frames to spread burst errors that would otherwise prevent recovery of data. Data encoded with redundancy is passed to one of a number of coders where the data rate and the number of

bits per pixel is assigned. It will be appreciated that a single coding option may be provided where the characteristics of the VCR are known and/or where the format of the transmitted data is uniform. However, it is advantageous to be able to select from a number of coders in order to enable the best modulation technique to be selected having regard to the format of the transmitted data and the characteristics of the VCR which is to be used to record the data. The apparatus is preferably programmable to select one of the available coders. More preferably, the device incorporates means for selecting the most appropriate coder. By carrying out trial recordings of data using different coding techniques and analysing the signals on playback, the record characteristics of the VCR can be assimilated and the coding method chosen which

produces the best results. This can be done automatically under the control of programming software. Alternatively the manufactures of a VCR may provide code information relating to the data record characteristics. Inputting this code to the processing apparatus will enable it to select which of the available coders is the most suitable.

There are two basic types of encoder illustrated. An NRZ encoder assigns a single bit per pixel, whereas other coder utilise multi-bit pixels. A multi-bit pixel is formed by first splitting a word into one or more groups of bits. These groups are then processed separately to form symbols that modulate two carriers of single frequency quadrature phase. These two carriers which are separated by a 90° phase shift are generated by a phased locked loop. The

two modulated carriers are then combined and filtered and passed to a gate circuit G which adds a start and end sequence to each data block.

Alternatively data can enter the gate through the symbol encoder path from the NRZ encoder, both are under control of a mode circuit which performs the selection and the clock rate which controls the number of data pixels per video line.

The data from the gate circuit is converted to an analog signal by the digital to analog converter means DAC, the resulting signal is added to a carrier reference and line and frame synchronisation signals. This combined signal is then mixed with the analog picture signal to form a combined data and picture signal. For a combined signal the data portion is usually restricted to a small number of the video lines, such as those in the vertical blanking interval

say of the order of 25.

It may be desirable to increase the number of lines to achieve higher data storage or to

accommodate a lower data rate associated with old or worn video recorders. Data lines that extend into the visible portion of the video frame can be blanked when the data is recovered to

prevent unwanted interference with the picture. The result is a black border at the top and/or bottom of the TV picture.

If no picture component is required the whole of the video frame is available for data 8

storage, such as for appending content related data down loaded from the Internet to the end of a recorded television program. It will be appreciated that pre-recorded video cassettes could be provided with data recorded onto them either as a supplement to audio/visual program material or otherwise.

Decoding of the recorded signal is described further hereinafter with reference to Figure 2b which illustrates a programmable data decoder. The video signal from video recorder is converted into a digital signal by an analog to digital converter means ADC. Data

from the ADC is passed to one of a plurality of different decoding schemes which are each the reverse of the ones used for encoding.

For single bit encoded pixels the Non Return to Zero (NRZ) is utilised. For multi-bit pixels the Quadrature Amplitude Modulation decoder is employed. Two carriers identical in phase and frequency to the original carriers are produced by the phase locked loop, these are multiplied with the digitised signal to reproduce after filtering the original multi-bit symbols that modulated the original earners. These symbols are converted into the original binary form by signal slicers.

The recovered bits are then combined to form a multi-bit binary word, which is passed

to the transposition memory to arrange the bits into the original sequence. Some of these bits will have been corrupted by the video processing circuits in the VCR. The Cyclic Redundancy Check (CRC) locates the errors, which are then conected by the Reed Solomon error correction scheme to recover the original data.

The carrier reference preamble (?) is transmitted just after Back Porch (BP) portion of 9

the video signal that follows the line synchronisation pulse (S) - see Figure 6. A sync detector detects each line sync pulse and through the line sync fly wheel PLL circuit (X) generates an enable pulse to the PLL that generates a phase locked carrier replica. If any individual line sync signal is lost the flywheel PLL generates the appropriate enable pulse with reference to previously received line syncs.

The start of a video frame is identified by the frame sequence detector (FSD) which through the frame sync flywheel PLL (Y) generates a video frame reference signal which is used to identify the data position in a video frame.

Figure 7 illustrates the recovered analog signal of one of the modulated carriers (one of two) after filtering. Also illustrated are two bits (two channels of one bit per symbol per carrier) forming two channels that were encoded on to the carrier and the recovered versions of each.

An example of the preferred error conection scheme is described hereinafter.

Figure 3 illustrates a block of data and the associated CRC scheme. Six rows of thirteen data words are encoded into six CRC check values P1-P6. A fault in any of the data words can be located to within a single row by this technique.

Locating the faulty word within a row utilises the Reed Solomon codes Ra S_a and Rb Sb illustrated in Figure 4. Error location is performed by the intersection of these three sets of

checksums and code words as illustrated in Figure 5. Errors are zeroed and then corrected utilising the Reed Solomon code words Ra S_a and Rb Sb.

Operation of the signal processing apparatus is conveniently controlled by an infra-red 10

controller. More particularly the infra-red controller of the set top box facilitates communication with the VCR to control VCR functions using for example a hand held I/R peripheral control unit.

The operator may wish to chose whether to record data associated with picture content and in some instances may wish to record only data. Thus it is proposed to provide a program controller which may be of wireless type - such as the typical infra-red remote controller, or of any other convenient type. Controlling the recording of picture content, associated transmitted data and other data is conveniently done from an on screen menu.

Claims

11CLAIMS

1. Signal processing apparatus comprising converter means operating on an input comprising data signals transmitted via or through terrestrial, cable or satellite television networks and comprising an error conection means to reduce stored errors and operable to generate an output in a form suitable for storage onto video tape.

2. Signal processing apparatus as claimed in claim 1 in which both coded digital data and conventional video pictures are stored on the same tape.

3. Signal processing apparatus as claimed in claims 1 or 2 in which said converter means operates on data transmitted in a vertical blanking interval.

4. Signal processing apparatus as claimed in claims 1, 2 or 3 further comprising programmable means to provide an adjustable storage rate.

5. Signal processing apparatus as claimed in anyone of claims 1 or 4 further comprising means to adjust the number and/or the position of lines used for the encoded digital data.

6. Signal processing apparatus as claimed in anyone of claims 1 to 5 further comprising programmable means to provide one of a plurality of selectable modulation techniques.

7. Signal processing apparatus as claimed in anyone of the preceding claims and further

comprising means for decoding data signals recorded onto magnetic storage tape into a format suitable for viewing on a television screen.

8. Signal processing apparatus as claimed in claim 7 further comprising means for blanking over lines of data during replay which would otherwise be visible on screen. 12

9. Signal processing apparatus as claimed in anyone of the preceding claims and further comprising supplementing the recorded data with data from other sources.

10. Signal processing apparatus as claimed in claim 9 in which the supplemental data is sourced from the Internet, via a modem or other means.

11. A method of recording on magnetic storage tape a signal transmitted via or through a

terrestrial, cable or satellite television network in comprising a data signal, comprising isolating the data signal and converting the recorded data into a form suitable for storage onto said magnetic storage tape passing the decoded signal to an error coder and performing an error detection and correction operation, and duly recording the results signed on to said magnetic storage tape viewing a video cassette recorder or such-like

means.

12. A method as claimed in claim 11 comprising operating on a signal received from a tuner to extract data from the vertical blanking interval using a Vertical Blanking Interval decoder.

13. A method as claimed in claims 11 or 12 in which the error coder adds redundancy to the

signal.

14. A method as claimed in claim 13 further comprising passing the data encoded with redundancy to a shuffle memory which transposes bits over several lines or frames to spread burst enors.

15. A method as claimed in anyone of claims 11 to 14 further comprising passing the recovered data to a coder which assigns the data rate and the number of bits per pixel. 13

16. A method as claimed in anyone of claims 11 to 15 and further comprising converting the data to an analogue signal and adding to a carrier reference and line and frame reference

signals.

17. A method as claimed in claim 16 comprising combining the processed data signals with any analogue picture signal recovered from the timer to form a combined data and picture signal in a format suitable for recording onto video tape.

18. A method as claimed in anyone of claims 11 to 17 further comprising arranging the number of lines of the video storage tape which are to be assigned for data storage.

19. A method of recording on magnetic storage tape a signal transmitted via or through a terrestrial, cable or satellite television network incorporating a data signal substantially as hereinbefore described with reference to the accompanying drawings.

20. Signal processing apparatus constructed and arranged substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.