Scrambling and descrambling a high definition TV signal
View Patent ↗Method and apparatus for scrambling a high definition television signal to discourage unauthorized recording of same. While recording per se is not prevented, the resulting recorded signal is rendered unusable due to an induced “wobble” between the active video and the associated sync pulses. The scrambled television signal is readily viewable on a compliant high definition television set which descrambles the HDTV signal using an encoded indication of the amount of wobble accompanying the HDTV signal. Also provided is a special interface to prevent unauthorized persons from using the indication of the amount of wobble so as to defeat the scrambling. Also provided are method and apparatus for defeating the scrambling method and hence allowing recording of the scrambled video signal.
1. A method for scrambling a high definition television (HDTV) signal, comprising the acts of:
providing the HDTV signal;
time shifting the active picture portion of scan lines of the HDTV signal relative to the line timing reference of each scan line; and
inserting into the HDTV signal an indication of the amount of the time shifting;
wherein a maximum amount of the time shifting is predetermined and is included in the HDTV signal in such a manner as not to be recordable by at least some video recorders.
2. The method of claim 1 , wherein the amount of the time shifting of each scan line is constant for all scan lines of a particular frame or field of the HDTV signal.
3. The method of claim 1 , wherein the line timing reference is a color burst or a synchronization pulse.
4. The method of claim 1 , further comprising the act of encoding the indication of the amount of time shifting into data of predetermined length.
5. The method of claim 1 , wherein the inserting includes inserting the indication of the amount of time shifting into a blanking interval of the HDTV signal.
6. The method of claim 5 , wherein the indication is modulation in time of a predetermined synchronization pulse in a preceding field or frame of the HDTV signal.
7. The method of claim 6 , further comprising the act of suppressing a pedestal level of the predetermined synchronization pulse.
8. The method of claim 6 , wherein the indication is modulation in time of a predetermined edge of the predetermined synchronization pulse.
9. The method of claim 1 , further comprising the act of varying the amount of the time shifting in each field or frame.
10. The method of claim 9 , wherein the variation is random or pseudo random.
11. The method of claim 1 , further comprising the acts of:
converting the provided HDTV signal to digital component format, prior to the time shifting;
time shifting each of the digital components; and converting the time shifted components to an analog HDTV signal.
12. A method of descrambling a scrambled high definition television (HDTV) signal, the scrambled HDTV signal having, in its active picture portion, video lines time shifted relative to the line timing reference of each video line, and having an indication of the amount of the time shifting associated with the HDTV signal in such a manner as not to be recordable by at least some video recorders, the descrambling comprising the acts of:
receiving the scrambled HDTV signal;
extracting from the scrambled HDTV signal the indication of the amount of time shifting;
generating a new line timing reference; and
establishing a stable relationship between the generated line timing reference and the active picture portion of the video lines, using the extracted indication of the time shifting.
13. The method of claim 12 , wherein the amount of the time shifting of each video line is constant for a particular frame or field of the HDTV signal.
14. The method of claim 12 , wherein the line timing reference is a color burst or a synchronization signal.
15. The method of claim 12 , wherein the indication of the amount of time shifting is encoded into data of predetermined length.
16. The method of claim 12 , wherein the indication of the amount of time shifting is inserted into a blanking interval of the HDTV signal.
17. The method of claim 12 , wherein the indication is in a predetermined synchronization pulse in each of a preceding field or frame of the HDTV signal.
18. The method of claim 17 , wherein a pedestal level of the predetermined synchronization pulse is suppressed.
19. The method of claim 17 , wherein the indication is a location of a predetermined edge of the predetermined synchronization pulse.
20. A high definition television (HDTV) receiver adapted to descramble a scrambled HDTV signal, comprising:
an input terminal for receiving the HDTV signal;
a separator circuit coupled to the input terminal and which extracts from the HDTV signal indications of time shifting of the active picture portion of video lines of the HDTV signal relative to the line timing reference of each line;
a phase lock loop coupled to the separator circuit, which generates a new line timing reference and establishes a stable relationship between the generated line timing reference and the active picture portion of the video lines using the extracted indications; and
a deflection circuit having an input terminal coupled to the phase lock loop and having an output terminal coupled to drive a television display.
21. The apparatus of claim 20 , wherein the amount of the time shifting of each video line is constant for a particular frame or field of the HDTV signal.
22. The apparatus of claim 20 , wherein the line timing reference is a color burst or synchronization signal.
23. The apparatus of claim 20 , wherein each indication of the amount of time shifting is encoded into data of predetermined length.
24. The apparatus of claim 20 , wherein each indication of the amount of time shifting is in a blanking interval of the HDTV signal.
25. The apparatus of claim 24 , wherein each indication of the amount of the time shifting is in a predetermined synchronization pulse in a preceding field or frame of the HDTV signal.
26. The apparatus of claim 25 , wherein a pedestal level of the predetermined synchronization pulse is suppressed.
27. The apparatus of claim 25 , wherein the indication is a location of a predetermined edge of the predetermined synchronization pulse.
28. The apparatus of claim 20 , wherein the separator circuit is coupled between the input terminal for receiving the HDTV signals and a video amplifier coupled to drive the television display.
29. The apparatus of claim 20 , further comprising a video amplifier coupled between the input terminal for receiving the HDTV signal and the separator circuit.
30. An apparatus for scrambling a high definition television (HDTV) signal, comprising:
an input terminal for receiving the HDTV signal;
a source of a time varying signal;
a storage coupled to the source of the varying signal and coupled to the input terminal, which time shifts the active portion of video lines of the HDTV signal by an amount determined by the varying signal, relative to the line timing reference of each video line;
a switch coupled to the storage and to the source of the time varying signal, thereby to insert into the HDTV signal an indication of the amount of the time shifting in such a manner as not to be recordable by at least some video recorders; and
an output terminal coupled to the switch and which outputs the time shifted HDTV signal with the inserted indication.
31. The apparatus of claim 30 , wherein the amount of the time shifting of each video line is constant for a particular frame or field of the HDTV signal.
32. The apparatus of claim 30 , wherein the line timing reference is a color burst or a synchronization pulse.
33. The apparatus of claim 30 , wherein the indication of the amount of time shifting is encoded into data of predetermined length.
34. The apparatus of claim 30 , wherein the indication of the amount of time shifting is inserted into a blanking interval of the HDTV signal.
35. The apparatus of claim 30 , wherein the indication is inserted into a predetermined synchronization pulse in a preceding field or frame of the HDTV signal.
36. The apparatus of claim 35 , wherein a pedestal level of the predetermined synchronization pulse is suppressed.
37. The apparatus of claim 35 , wherein the indication is a location of a predetermined edge of the predetermined synchronization pulse.
38. The apparatus of claim 30 , wherein the apparatus varies the amount of the time shifting in each field or frame.
39. The apparatus of claim 30 , wherein the variation in the time varying signal is random or pseudo random.
40. The apparatus of claim 30 , wherein the received HDTV signal is in digital form and the signal at the output terminal is in analog form.
41. The apparatus of claim 30 , further comprising a pulse generator coupled between the switch and the source of the time varying signal, thereby to insert a representation of the time shifting into the blanking interval.
42. A method of coupling a scrambled high definition television (HDTV) signal between a source and an HDTV receiver, wherein a coded pulse for descrambling the HDTV signal is located at a predetermined portion of a blanking interval of the scrambled HDTV signal, comprising the acts of:
transmitting the HDTV signal in analog form from the source;
conveying the transmitted HDTV signal on a conductor to the receiver;
except when the predetermined portion of the HDTV signal is being conveyed, providing a standard video connection on the conductor between the source and the receiver; and
when the predetermined portion is being conveyed, transmitting that portion of the HDTV signal as a current signal on the conductor.
43. The method of claim 42 , further comprising clipping a voltage of the HDTV signal when the predetermined portion is being conveyed.
44. An output interface in a source of scrambled high definition television (HDTV) signal wherein a coded pulse for descrambling the HDTV signals is located at a predetermined portion of a blanking interval of the scrambled HDTV signal, the interface comprising:
an input terminal for receiving the scrambled HDTV signal;
an output terminal for connecting to a HDTV receiver; and
an interface circuit coupled to a node between the input and output terminals and having a control terminal coupled to receive a control signal, wherein during the predetermined portion of the blanking interval, in response to the control signal, the interface circuit provides a current signal to the output terminal to be included in the scrambled HDTV signal to be output to the HDTV receiver on the output terminal.
45. An input interface in a high definition television (HDTV) receiver adapted for descrambling a received scrambled HDTV signal including a coded pulse located at a predetermined portion of the scrambled HDTV signal, the interface comprising:
an input terminal for connecting to a source of the scrambled HDTV signal;
an output terminal connected to display circuitry of the receiver; and
an interface circuit coupled to a node between the input and output terminals and having a control terminal for receiving a control signal indicating the predetermined portion of the HDTV signal, wherein during the predetermined portion, in response to the control signal and an input current signal, the interface circuit provides a corresponding signal to the output terminal.
46. A method of modifying a high definition television (HDTV) signal which has been subject to time shifting of the active video in a video line relative to a timing reference of the line, wherein an indication of the amount of time shifting is associated with the HDTV signal and not recordable by at least some video recorders, for inhibiting the making of acceptable recordings of the HDTV signal therefrom, the method comprising the acts of:
receiving the HDTV signal including the associated indication of the amount of time shifting;
modifying the HDTV signal so that the indication of the amount of time shifting is recordable; and
recording the HDTV signal along with the indication of the amount of time shifting, thereby to permit later playback of a more acceptable video recording of the HDTV signal.
47. The method of claim 46 , wherein the act of modifying includes at least one of:
a) level shifting the indication;
b) level shifting at least a portion of the indication;
c) increasing an amplitude of at least a portion of the indication;
d) placing the indication in an above black level portion of the HDTV signal;
e) placing the indication in an active video portion of the HDTV signal;
f) placing the indication in an audio channel associated with the HDTV signal; and
g) encoding the indication and placing the encoded indication in a blanking interval of the HDTV signal.
48. The method of claim 46 , wherein the act of modifying includes modifying the HDTV signal so that at least a portion of the HDTV signal carrying the indication is recordable.
49. The method of claim 46 , wherein the act of modifying includes providing the indication in a recordable portion of the HDTV signal.
50. The method of claim 46 , wherein the act of modifying includes:
extracting the indication from the HDTV signal; and
conveying the extracted indication in a channel not carrying a remainder of the HDTV signal.
51. The method of claim 46 , wherein the act of recording includes converting the HDTV signal to digital form, and wherein the act of modifying includes changing an amplitude of at least a portion of the HDTV signal carrying the indication, prior to the converting, to a level at which the indication can be converted to the digital form.
52. The method of claim 51 , further comprising changing an amplitude of an active picture portion of the HDTV signal.
53. The method of claim 51 , wherein the indication is at an edge of a sync pulse in the HDTV signal, and the act of modifying includes changing an amplitude of at least the edge of the sync pulse.
54. The method of claim 46 , wherein the act of recording includes converting the HDTV signal to digital form, and wherein the act of modifying includes moving a portion of the HDTV signal carrying the indication to a location in the HDTV signal, wherein the indication is a pulse train.
55. The method of claim 50 , wherein the act of conveying includes modulating the indication onto an audio frequency carrier signal on an audio channel.
56. The method of claim 46 , wherein the act of modifying includes:
extracting the indication;
coding the indication; and
inserting the coded indication into a predetermined portion of the HDTV signal.
57. The method of claim 56 , wherein the predetermined portion is one of active video or a blanking interval.
58. The method of claim 46 , wherein the act of modifying includes:
correcting time shifting between the active video and the timing reference in the video line, prior to the act of recording, thereby obviating the need to record the indication of the amount of time shifting.
59. The method of claim 58 , further comprising correcting any time base error in the video line after the correcting of the time shifting.
60. An apparatus for modifying a high definition television (HDTV) signal which has been subject to time shifting of the active video in a video line relative to a timing reference of the video line, wherein an indication of the amount of the time shifting is associated with the HDTV signal and not recordable by at least some video recorders, for inhibiting the making of acceptable recordings of the HDTV signal therefrom, the apparatus comprising:
an input terminal for receiving the HDTV signal including the associated indication of the amount of time shifting;
modifier circuitry coupled to the input terminal and processing the HDTV signal so the indication of the amount of time shifting is modified so as to be recordable; and
an output terminal coupled to the modifier circuitry for outputting the modified HDTV signal to a video recorder.
61. The apparatus of claim 60 , wherein the modifier circuitry does one of:
a) level shifting the indication;
b) level shifting at least a portion of the indication;
c) increasing an amplitude of at least a portion of the indication;
d) placing the indication in an above black level portion of the HDTV signal;
e) placing the indication in an active video portion of the HDTV signal;
f) placing the indication in an audio channel associated with the HDTV signal; and
g) encoding the indication and placing the encoded indication in a blanking interval of the HDTV signal.