# US 7,609,836 B2 · Seamless switching between multiple pre-encrypted video files

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- Number: US 7,609,836 B2
- Document ID: US7609836B2
- Status: Granted
- Kind: B2
- Application number: 11/759,014
- Filed: 2007-06-06
- Published: 2007-10-04
- Granted: 2009-10-27
- Earliest claimed: 2003-06-06
- Assignees: General Instrument Corporation
- Inventors: Lawrence D. Vince
- Web page: https://patentgrep.com/patent/US7609836B2

## CPC

- H04N 21/23473: {by pre-encrypting}
- H04N 7/1675: {Providing digital key or authorisation information for generation or regeneration of the scrambling sequence (pseudo-random number generators in general G06F7/58)}
- H04N 7/17336: {Handling of requests in head-ends}
- H04N 21/234381: {by altering the temporal resolution, e.g. decreasing the frame rate by frame skipping}
- H04N 21/2387: Stream processing in response to a playback request from an end-user, e.g. for trick-play
- H04N 21/26606: {for generating or managing entitlement messages, e.g. Entitlement Control Message [ECM] or Entitlement Management Message [EMM] (arrangements for conditional access to broadcast information or to broadcast-related services H04H60/14)}
- H04N 21/47202: {for requesting content on demand, e.g. video on demand}
- H04N 21/6587: Control parameters, e.g. trick play commands, viewpoint selection
- H04N 21/8541: involving branching, e.g. to different story endings
- H04N: PICTORIAL COMMUNICATION, e.g. TELEVISION

## Abstract

In a video on demand (VOD) system, methods and apparatus are provided for seamlessly switching back and forth between two pre-encrypted files having changing encryption keys Such switching back and forth may be required when a VOD server stores both a “normal” copy of a movie and a “special” copy such as a “trick-play” version for, e g, fast forward and rewind effects Instead of using keys with changing parities in both streams, the special stream is encrypted with keys using the same parity (even or odd), while the normal stream is encrypted with one dynamic key (odd or even) and one fixed key (even or odd) Other special streams, such as scene branch streams and alternate angle streams can also be accommodated.

## Claims

### Claim 1

A method for delivery of pre-encrypted program content comprising: encoding master content into digital form; encrypting the master content in its entirety; storing the encoded, encrypted content in a VOD server from which it can be broadcast, on demand, to end-users; wherein: the master content comprises a first file and a second file which is associated with the first file; the first file is encrypted according to a first encryption scheme using a fixed key having a fixed parity alternating with a changing key having a second parity opposite the fixed parity; the second file is encrypted according to a second encryption scheme using the fixed key; and in response to a request from an end-user, delivering the encoded, encrypted content to the end-user.

### Claim 2 (depends on 1)

A method in accordance with claim 1, wherein the first file is a normal file and the second file is a scene branch file.

### Claim 3 (depends on 1)

A method in accordance with claim 1, wherein the first file is a normal file and the second file is an alternate camera angle file.

### Claim 4 (depends on 1)

A method in accordance with claim 1, wherein: the master content is encoded using the MPEG-2 standard.

### Claim 5 (depends on 1)

A method in accordance with claim 1, wherein: the first file is a normal file; and the second file is a trick play file.

### Claim 6 (depends on 1)

A method in accordance with claim 1, wherein: the second file is appended to the first file.

### Claim 7 (depends on 1)

A method in accordance with claim 1, wherein: the second file is encrypted after the first file is encrypted.

### Claim 8 (depends on 1)

A method in accordance with claim 1, wherein: the first file is a normal file; the second file is a trick play file; the second file is encrypted after the first file is encrypted; and the encrypted second file is appended to the encrypted first file.

### Claim 9

A method for delivery of pre-encrypted program content comprising:
encoding master content into digital form;
dividing the master content into first and second files, wherein the first file includes a first sequence of groups of transport packets and the second file includes a second sequence of groups of transport packets;
encrypting alternating groups in the first sequence with a fixed key and encrypting remaining groups in the first sequence with a changing key;
encrypting each of the groups in the second sequence with the fixed key;
storing the encoded, encrypted master content in a VOD server from which it can be broadcast, on demand, to end-users; and
in response to a request from an end-user, delivering the encoded, encrypted content to the end-user.