Trick mode system
View Patent ↗A method is described for trick mode playback, the method including selecting a key-frame in a recording substantially in the vicinity of a trick mode playback starting position, preparing a decryption key associated with a key period including the selected key-frame, sending the prepared decryption key to a descrambler, thereby enabling decryption of video beginning at the selected key-frame, sending a first number P seconds of decrypted video frames, starting at the selected key-frame, at a predetermined speed for a predetermined number of seconds, to a video decoder, in parallel to the sending P seconds of video frames, choosing at least a second video section to stream to the video decoder, sending a decryption key associated with the chosen second video section to the descrambler, and repeating the steps of selecting, preparing, sending the prepared decryption key, and sending a first number P seconds of decrypted video frames. Related apparatus and methods are also described.
1. A method for trick mode playback, the method including:
selecting a key-frame in a recording substantially in the vicinity of a trick mode playback starting position;
preparing a first decryption key associated with a key period including the selected key-frame;
sending the prepared first decryption key to a descrambler, thereby enabling decryption of video beginning at the selected key-frame;
sending a first number P seconds of decrypted video frames, starting at the selected key-frame, at a predetermined speed for a predetermined number of seconds, to a video decoder;
in parallel to the sending the P seconds of video frames, choosing at least a second video section to stream to the video decoder;
sending a second decryption key associated with the chosen second video section to the descrambler; and
repeating the steps of:
selecting;
preparing;
sending the prepared first decryption key; and
sending a first number P seconds of decrypted video frames.
2. The method according to claim 1 and wherein the choosing includes defining a new starting position based, at least in part, on the following: the previous starting position; P; and a second number J seconds of video to be skipped.
3. The method according to claim 1 and wherein the recording is encrypted in accordance with a data stream encryption scheme not using ECM and key polarity, and the vicinity includes three consecutive key periods, the middle of the three consecutive key periods including a candidate key period.
4. The method according to claim 2 and wherein the recording is encrypted in accordance with a data stream encryption scheme not using ECM and key polarity, and the vicinity includes three consecutive key periods, the middle of the three consecutive key periods including a candidate key period.
5. The method according to claim 1 and wherein the recording is encrypted in accordance with a data stream encryption scheme using ECM and key polarity, and the vicinity includes one of:
if a candidate key period has the same key polarity as previous frames which were streamed, the vicinity includes:
a key period immediately before the candidate's position; and
a key period immediately after the candidate's position; and
if the candidate key period has the opposite key polarity as previous frames which were streamed, the vicinity includes:
the candidate position's key period;
a key period two key periods prior to the candidate key period; and
a key period two key periods after the candidate key period.
6. The method according to claim 2 and wherein the recording is encrypted in accordance with a data stream encryption scheme using ECM and key polarity, and the vicinity includes one of:
if a candidate key period has the same key polarity as previous frames which were streamed, the vicinity includes:
a key period immediately before the candidate's position; and
a key period immediately after the candidate's position; and
if the candidate key period has the opposite key polarity as previous frames which were streamed, the vicinity includes:
the candidate position's key period;
a key period two key periods prior to the candidate key period; and
a key period two key periods after the candidate key period.
7. A trick mode playback apparatus, the apparatus including:
a key-frame selector, which selects a key-frame in a recording, the key frame being substantially in the vicinity of a trick mode playback starting position;
a decryption key preparer, operative to prepare a first decryption key associated with a key period including the selected key-frame;
a transmitter which transmits the prepared first decryption key to a descrambler, thereby enabling decryption of video beginning at the selected key-frame;
a video decryptor which sends a first number P seconds of decrypted video frames, starting at the selected key-frame, at a predetermined speed for a predetermined number of seconds, to a video decoder;
a video selector which, in parallel to the video decryptor sending the P seconds of video frames, chooses at least a second video section to stream to the video decoder; and
a decryption key transmitter which sends a second decryption key associated with the chosen second video section to the descrambler;
wherein the trick mode playback apparatus is operative to iteratively repeat the:
selecting the key frame;
preparing the first decryption key;
transmitting the prepared first decryption key; and
sending a first number P seconds of decrypted video frames.
8. The apparatus according to claim 7 and wherein the video selector chooses a new starting position based, at least in part, on the following: the previous starting position; P; and a second number J seconds of video to be skipped.
9. The apparatus according to claim 7 and wherein the recording is encrypted in accordance with a data stream encryption scheme not using ECM and key polarity, and the vicinity includes three consecutive key periods, the middle of the three consecutive key periods including a candidate key period.
10. The apparatus according to claim 8 and wherein the recording is encrypted in accordance with a data stream encryption scheme not using ECM and key polarity, and the vicinity includes three consecutive key periods, the middle of the three consecutive key periods including a candidate key period.
11. The apparatus according to claim 7 and wherein the recording is encrypted in accordance with a data stream encryption scheme using ECM and key polarity, and the vicinity includes one of:
if a candidate key period has the same key polarity as previous frames which were streamed, the vicinity includes:
a key period immediately before the candidate's position; and
a key period immediately after the candidate's position; and
if the candidate key period has the opposite key polarity as previous frames which were streamed, the vicinity includes:
the candidate position's key period;
a key period two key periods prior to the candidate key period; and
a key period two key periods after the candidate key period.
12. The apparatus according to claim 8 and wherein the recording is encrypted in accordance with a data stream encryption scheme using ECM and key polarity, and the vicinity includes one of:
if a candidate key period has the same key polarity as previous frames which were streamed, the vicinity includes:
a key period immediately before the candidate's position; and
a key period immediately after the candidate's position; and
if the candidate key period has the opposite key polarity as previous frames which were streamed, the vicinity includes:
the candidate position's key period;
a key period two key periods prior to the candidate key period; and
a key period two key periods after the candidate key period.
13. Trick mode playback apparatus comprising:
means for selecting a key-frame in a recording, the key frame being substantially in the vicinity of a trick mode playback starting position;
means for preparing a first decryption key associated with a key period including the selected key-frame;
means for transmitting the prepared first decryption key to a descrambler, thereby enabling decryption of video beginning at the selected key-frame;
means for decrypting video, the means for decrypting video sending a first number P seconds of decrypted video frames, starting at the selected key-frame, at a predetermined speed for a predetermined number of seconds, to a video decoder;
means for selecting video, the means for selecting video selecting at least a second video section to stream to the video decoder, in parallel to the means for decrypting video sending the P seconds of video frames; and
means for transmitting a second decryption key to the descrambling means, the second decryption key being associated with the chosen second video section;
wherein the trick mode playback apparatus is operative to iteratively repeat the:
selecting the key frame;
preparing the first decryption key;
transmitting the prepared first decryption key; and
sending a first number P seconds of decrypted video frames.