Systems and methods for playing back alternative streams of protected content protected using common cryptographic information

1. A playback device, comprising:

a processor;

non-volatile memory containing a client application comprising a set of machine readable instructions;

wherein the set of machine readable instructions configures the processor to:

register with a content distribution system in order to obtain cryptographic data bound to the playback device from the content distribution system;

request adaptive bitrate streaming of protected video from the content distribution system using the bound cryptographic data;

obtain a top level index file from the content distribution server, wherein the top level index file identifies a plurality of alternative streams of protected video that have been protected by a common set of frame keys generated by a source encoder, and wherein the top level index file comprises (i) an encrypted copy of a first key from the common set of frame keys and (ii) a set of DRM information that identifies protected portions of the alternative streams of protected video and frame keys to utilize in accessing the protected portions of the alternative streams;

obtain a first portion of protected video from a given stream of protected video from the content distribution system, wherein the first portion of protected video is protected by the first key from the common set of frame keys;

decrypt the encrypted copy of the first key using the bound cryptographic data;

decrypt the first portion of protected video using the decrypted first key according to the obtained set of DRM information;

playback the decrypted first portion of video from the given stream;

obtain a second portion of protected video from the given stream of protected video from the content distribution system, wherein the second portion of protected video is protected by a second key from the common set of frame keys;

obtain an encrypted copy of the second key from the common set of frame keys from the source encoder, wherein the encrypted copy of the second key has been generated by the source encoder;

decrypt the encrypted copy of the second key using the bound cryptographic data;

decrypt the second portion of protected video using the decrypted second key according to the obtained set of DRM information; and

playback the decrypted second portion of video from the given stream.

2. The playback device of claim 1 , wherein:

the alternative streams of protected video are encoded at different maximum bitrates using different sets of encoding parameters; and

the set of machine readable instructions further configures the processor to decode the encoded frames of video prior to playback of the obtained portions of video.

3. The playback device of claim 1 , wherein:

the plurality of alternative streams of protected video are contained in container files that comprise at least one header that includes information that describes the encoding of the stream of protected video; and

the top level index file identifies the location of the at least one header within each container file.

4. The playback device of claim 3 , wherein:

each container file containing one of the alternative streams of protected video further comprises an index; and

the set of machine readable instructions further configures the processor to:

request at least a portion of an index from the given container file;

identify the portion of the given container file containing a specific portion of video using the index; and

request the identified portion of the given container file.

5. The playback device of claim 3 , wherein the container files are Matroska container files.

6. The playback device of claim 5 , wherein the common set of frame keys is stored in a common DRM Header element contained within a Tracks element within each of the Matroska container files containing the alternative streams of protected video.

7. The playback device of claim 1 , wherein the common set of frame keys is part of a frame key table that is common to each of the plurality of alternative streams.

8. The playback device of claim 1 , wherein the set of machine readable instructions further configures the processor to securely receive a content key, and wherein the common set of frame key is encrypted.

9. The playback device of claim 8 , wherein the set of machine readable instructions further configures the processor to:

obtain the content key that can be used to decrypt the encrypted common set of frame keys; and

decrypt the common set of frame keys using the obtained content key.

10. The playback device of claim 8 , wherein the set of machine readable instructions configures the processor to obtain a common DRM Header element by requesting a Tracks element from a Matroska container file identified in the top level index file.

11. The playback device of claim 5 , wherein:

each Mastroska container file containing an alternative stream of protected video further comprises an index contained within a Cues element; and

the set of machine readable instructions further configures the processor to request a portion of video from one of the Matroska container files by configuring the processor to:

request at least a portion of a Cues element from a Matroska container file containing one of the alternative streams of protected video;

identify a portion of the Matroska container file containing a specific portion of video using at least one CueTrackPosition element within the Cues element; and

request the portion of the Matroska container file identified by the at least one CueTrackPosition element.

12. The playback device of claim 11 , wherein the index comprises a plurality of CueTrackPosition elements that identify the location of a plurality of Cluster elements within the Matroska container file.

13. The playback device of claim 12 , wherein:

each Cluster element contains a plurality of BlockGroup elements including encoded portions of video;

a CueTrack Position element indexes each Cluster element; and

each CueTrackPosition element includes the size of the Cluster element that it indexes.

14. The playback device of claim 11 , wherein:

each of the Matroska container files containing an alternative stream of protected video includes a set of BlockGroup elements that each contain a DRMInfo element and an encrypted frame of video, where the DRMInfo element is a part of the set of DRM information for each of the Matroska container files; and

the set of machine readable instructions further configures the processor to decrypt encrypted video frames of the obtained portions of video using the decrypted copy of the common set of frame keys by configuring the processor to:

obtain a BlockGroup containing an encrypted frame of video;

parse the BlockGroup element to obtain a DRMInfo element indicating at least a portion of the encrypted frame of video that is encrypted using a frame key from the common set of frame keys;

decrypt the at least one encrypted portion of the encrypted frame of video using the identified frame key; and

decode the frame of video.

15. A method comprising:

registering a playback device with a content distribution system in order to obtain cryptographic data bound to the playback device from the content distribution system using the playback device;

requesting adaptive bitrate streaming of protected video from the content distribution system using the bound cryptographic data and using the playback device;

obtaining a top level index file from the content distribution server using the playback device, wherein the top level index file identifies a plurality of alternative streams of protected video that have been protected by a common set of frame keys generated by a source encoder, and wherein the top level index file comprises (i) an encrypted copy of a first key from the common set of frame keys and (ii) a set of DRM information that identifies protected portions of the alternative streams of protected video and frame keys to utilize in accessing the protected portions of the alternative streams;

obtaining a first portion of protected video from a given stream of protected video from the content distribution system using the playback device, wherein the first portion of protected video is protected by the first key from the common set of frame keys;

decrypting the encrypted copy of the first key using the bound cryptographic data and the playback device;

decrypting the first portion of protected video using the decrypted first key according to the obtained set of DRM information using the playback device;

playing back the decrypted first portion of video from the given stream using the playback device;

obtaining a second portion of protected video from the given stream of protected video from the content distribution system using the playback device, wherein the second portion of protected video is protected by a second key from the common set of frame keys;

obtaining an encrypted copy of the second key from the common set of frame keys from the source encoder using the playback device, wherein the encrypted copy of the second key has been generated by the source encoder;

decrypting the encrypted copy of the second key using the bound cryptographic data and using the playback device;

decrypting the second portion of protected video using the decrypted second key according to the obtained set of DRM information and using the playback device; and

playing back the decrypted second portion of video from the given stream using the playback device.