Generation of encrypted video information
View Patent ↗An encrypted stream of video information ( 20 ) contains first video frames ( 22 ) and second video frames which are accessible and not accessible during trick play respectively. From a source stream encrypted that is for decryption with repeatedly changing control words sections of the stream are identified where respective first ones of the frames occur in the stream. Control words for decryption ( 24 ) are included in the stream. At least part of the control words are included in the stream at positions selected synchronized to the identified sections.
1. A method of generating an encrypted stream of video information that represents video frames, the video frames comprising a plurality of first video frames accessible during a special mode of play and a plurality of second video frames not accessible during a special mode of play, the method comprising:
encrypting the video information to produce an encrypted stream for decryption with control words, the stream of encrypted video information being divided into successive crypto-periods, each of the successive crypto-periods requiring a respective control word for decryption of the encrypted stream of video information: identifying a plurality of sections of the source stream of video information that represent the plurality of first video frames;
providing items of decryption information each comprising a first control word and a second control word for decryption of the encrypted stream of video information; and
inserting items of decryption information into the encrypted stream in each of the plurality of successive crypto-periods, at least some of the items of decryption information being inserted into the encrypted stream of video information at times synchronized to first video frames, wherein:
the first control word is configured to decrypt the encrypted stream during a current crypto-period that is the crypto-period in which the decryption information is inserted;
the second control word is configured to decrypt the encrypted stream during another one of the plurality of crypto-periods;
for the items of decryption information located substantially in a first half of a crypto-period, the second control word is configured to decrypt the encrypted stream during the crypto-period that precedes the crypto-period in which the decryption information is inserted thereby providing the next past control word required for reverse play; and
for items of decryption information located substantially in a second half of a crypto-period, the second code word is configured to decrypt the encrypted video stream during the crypto-period that follows the crypto-period in which the decryption information is inserted thereby providing the next future control word required for forward play.
2. The method according to claim 1 further comprising:
selecting the plurality of first video frames based on a detection of video frames that are decodable without reference to other video frames; and
inserting the items of decryption information into a position within the one of the plurality of successive crypto-periods such that the position is synchronized to the plurality of sections, wherein each of the plurality of sections start and end with information from one of the plurality of first video frames.
3. The method according to claim 2 further comprising inserting a respective item of decryption information in each of the plurality of sections.
4. A method of generating an encrypted stream of video information that represents video frames, the video frames comprising a plurality of first video frames accessible during a special mode of play and a plurality of second video frames not accessible during a special mode of play, the method comprising:
encrypting the video information to produce an encrypted stream for decryption with control words, the stream of encrypted video information being divided into successive crypto-periods, each of the successive crypto-periods requiring a respective control word for decryption of the encrypted stream of video information;
identifying a plurality of sections of the source stream of video information that represent the plurality of first video frames;
providing items of decryption information each comprising a first control word and a second control word for decryption of the encrypted stream of video information; and
inserting items of decryption information into the encrypted stream in each of the plurality of successive crypto-periods, at least some of the items of decryption information being inserted into the encrypted stream of video information at times synchronized to first video frames, wherein:
the first control word is configured to decrypt the encrypted stream during a current crypto-period that is the crypto-period in which the decryption information is inserted;
the second control word is configured to decrypt the encrypted stream during another one of the plurality of crypto-periods;
for the items of decryption information located substantially in a first half of a crypto-period, the second control word is configured to decrypt the encrypted stream during the crypto-period that precedes the crypto-period in which the decryption information is inserted thereby providing the next past control word required for reverse play;
for items of decryption information located substantially in a second half of a crypto-period, the second code word is configured to decrypt the encrypted video stream during the crypto-period that follows the crypto-period in which the decryption information is inserted thereby providing the next future control word required for forward play;
storing the encrypted stream; and
selectively retrieving parts of the encrypted stream in a trick play mode, including the plurality of sections.
5. A storage medium configured to store an encrypted stream of video information representing video frames, the encrypted stream of video information comprising:
a plurality of sections comprising a plurality of first video frames accessible during a special mode of play; a plurality of second video frames not accessible during a special mode of play;
the encrypted stream being encrypted for decryption with control words;
the stream of encrypted video information being divided into successive crypto-periods, each of the successive crypto-periods requiring a respective control word for decryption of the encrypted stream; and
the encrypted stream also comprising items of decryption information each comprising a first control word and a second control word, wherein:
the items of decryption information are inserted into the encrypted stream in each of the plurality of successive crypto-periods;
at least some of the items of decryption information being inserted into the encrypted stream of video information at times synchronized to first video frames;
the first control word is configured to decrypt the encrypted stream during a current crypto-period that is the crypto-period in which the decryption information is inserted;
the second control word is configured to decrypt the encrypted stream during another one of the plurality of crypto-periods;
for the items of decryption information located substantially in a first half of a crypto-period, the second control word is configured to decrypt the encrypted stream during the crypto-period that precedes the crypto-period in which the decryption information is inserted thereby providing the next past control word required for reverse play; and
for items of decryption information located substantially in a second half of a crypto-period, the second code word is configured to decrypt the encrypted video stream during the crypto-period that follows the crypto-period in which the decryption information is inserted thereby providing the next future control word required for forward play.
6. The encrypted stream according to claim 5 , further comprising an item of decryption in each of the plurality of sections.
7. Dallard discloses an apparatus for generating an encrypted stream of video information, the stream of video information representing a plurality of first video frames accessible during a special mode of play and a plurality of second video frames not accessible during a special mode of play, the apparatus comprising:
a video source unit configured to provide a source stream of video information;
an encryption unit to encrypt the source stream to produce an encrypted stream for decryption with control words, the stream of encrypted video information being divided into successive crypto-periods, each of the successive crypto-periods requiring a respective control word for decryption of the encrypted stream of video information;
a section identification unit configured to identify a plurality of sections of the source stream of video information including the plurality of first video frames;
a control word generator configured to provide items of decryption information each comprising a first control word and a second control word for decryption of the encoded video stream; and
an insertion unit configured to insert the items of decryption information into each of the plurality of successive crypto-periods, wherein:
the first control word is configured to decrypt the encrypted stream during a current crypto-period that is the crypto-period in which the decryption information is inserted;
the second control word is configured to decrypt the encrypted stream during another one of the plurality of crypto-periods;
for the items of decryption information located substantially in a first half of a crypto-period, the second control word is configured to decrypt the encrypted stream during the crypto-period that precedes the crypto-period in which the decryption information is inserted thereby providing the next past control word required for reverse play; and
for items of decryption information located substantially in a second half of a crypto-period, the second code word is configured to decrypt the encrypted video stream during the crypto-period that follows the crypto-period in which the decryption information is inserted thereby providing the next future control word required for forward play.
8. The apparatus according to claim 7 wherein the selection identification unit is further configured to select the plurality of first video frames based on a detection of video frames that are decodable without reference to other video frames, and the insertion unit is further configured to insert the items of decryption information into a position within the successive crypto-periods such that the position is synchronized to the plurality of sections, wherein each of the plurality of sections start and end with information from one of the plurality of first video frames.
9. The apparatus according to claim 8 wherein the insertion unit is further configured to insert a respective item of decryption information in each of the plurality of sections.
10. A computer readable medium configured to store an encrypted stream of video information representing video frames, the encrypted stream of video information comprising:
a plurality of sections comprising a plurality of first video frames accessible during a special mode of play;
a plurality of second video frames not accessible during a special mode of play;
the encrypted stream being encrypted for decryption with control words;
the stream of encrypted video information being divided into successive crypto-periods, each of the successive crypto-periods requiring a respective control word for decryption of the encrypted stream; and
the encrypted stream also comprising items of decryption information each comprising a first control word and a second control word, wherein:
the items of decryption information are inserted into the encrypted stream in each of the plurality of successive crypto-periods;
at least some of the items of decryption information being inserted into the encrypted stream of video information at times synchronized to first video frames;
the first control word is configured to decrypt the encrypted stream during a current crypto-period that is the crypto-period in which the decryption information is inserted;
the second control word is configured to decrypt the encrypted stream during another one of the plurality of crypto-periods;
for the items of decryption information located substantially in a first half of a crypto-period, the second control word is configured to decrypt the encrypted stream during the crypto-period that precedes the crypto-period in which the decryption information is inserted thereby providing the next past control word required for reverse play; and
for items of decryption information located substantially in a second half of a crypto-period, the second code word is configured to decrypt the encrypted video stream during the crypto-period that follows the crypto-period in which the decryption information is inserted thereby providing the next future control word required for forward play.