Patent Publication Number: US-8117638-B2

Title: System and method for improved multi-stream multimedia transmission and processing

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a divisional of U.S. patent application Ser. No. 09/871,547, filed May 30, 2001, for “System and Method for Improved Multi-Stream Multimedia Transmission and Processing,” which is incorporated herein by reference. 
     BACKGROUND 
     1. Field of the Invention 
     This invention relates generally to the field of multimedia systems. More particularly, the invention relates to a system and method for multimedia simulcast using different encryption and/or compression techniques. 
     2. Description of the Related Art 
     As illustrated in  FIG. 1 , the “headend” in a cable television network is the facility where video feeds from various content providers (e.g., HBO, NBC, FOX, . . . etc) are received via satellite dish  108  and/or television antenna  109 , processed by headend equipment  100  and transmitted to cable subscribers. Headend equipment  100  for processing the video feeds typically includes one or more MPEG-2 compression modules  101 ; conditional access (“CA”) encryption modules  103  and  105 ; and quadrature amplitude modulation (“QAM”) modules  110 . 
     The MPEG-2 compression modules  101  compress any incoming video streams which have not already been compressed according to the MPEG-2 video compression standard. As indicated in  FIG. 1 , if the video content has already been compressed by the content provider, additional MPEG-2 compression will not be required at the headend (represented by the MPEG-2 stream feeding CA module  105 ). 
     Once compressed, the video content may be encrypted by conditional access (“CA”) encryption modules  103 ,  105  to prevent users from viewing content which they do not have the right to view (e.g., subscription-based content such as HBO or pay-per-view channels). Standard CA encryption systems are well known in the art and are currently manufactured by only a relatively small group of companies including Scientific Atlanta™, Motorola™, and News Data Systems™. 
     As indicated in  FIG. 1 , not all video content transmitted over cable networks is encrypted. For example, analog channels are transmitted unencrypted over most cable networks. As such, to prevent users from illegally viewing the analog channels, cable companies must physically disconnect the user&#39;s home from the cable network (e.g., using remote disconnect mechanisms such as a “trap” or a manual disconnect at the user&#39;s home by a cable technician). 
     The encrypted and/or unencrypted channels are then modulated and statistically multiplexed by a quadrature amplitude modulation (“QAM”) module  110 . As is known in the art, QAM uses phase and amplitude shaping to define a string of digital data. Cable companies generally use 64 QAM or 256 QAM modulation techniques, which transmit digital content using 6-bit or 8-bit symbols, respectively. Certain multimedia systems (primarily satellite systems) use a different modulation technique known as Differential Phase Shift Keying (“DPSK”) rather than QAM to modulate the video content. Once the digital content has been QAM-modulated, it is transmitted across the cable system via one or more RF modulators  115 . Note that the analog signal in  FIG. 1  is fed directly into the RF modulators  115  for transmission over the cable network (i.e., it is not encrypted or QAM-modulated). 
     As illustrated in  FIG. 1 , an allocation of all available bandwidth  120  on a cable network typically includes an unencrypted analog component  121 , a compressed and encrypted digital component  122  (compressed via MPEG-2 and encrypted using standard encryption as described above), and a third miscellaneous component reserved for transmitting various types of control signals and data (e.g., according to the DOCSIS cable modem standard). 
     As illustrated in  FIG. 2 , a typical multimedia receiver  120  (referred to generally as a “set-top box”) for receiving cable or satellite channels includes one or more tuners  210  which lock on to the video signal  200  at a particular carrier frequency and down-convert the signal to a baseband signal. A QAM demodulator  220  then demodulates the baseband video signals; a CA decryption module  230  decrypts the digital video content contained in the video signal using a series of decryption keys provided via a secure micro unit (not shown); and an MPEG-2 decoder module  240  decompresses the content. An NTSC encoder  250  may also be used to encode the digital video content so that it may be properly displayed on a standard NTSC television  260 . As indicated in  FIG. 2 , if the analog signal is not encrypted, it may be transmitted directly through to the television  260  following demodulation. 
     One problem which exists with the foregoing configuration is that cable operators are unable to change the types of encryption and/or compression used for transmitting video content without upgrading all of the multimedia receivers used by current subscribers. For example, the standard CA decryption modules  230  found in current multimedia receivers are incapable of decrypting content using a non-standard encryption algorithm. Similarly, multimedia receivers equipped with MPEG-2 decoder modules  240  are only capable of decompressing video content according to the MPEG-2 standard. As such, cable operators are unable to realize the benefits of more advanced compression algorithms (e.g., such as MPEG-4 and RealVideo™ 8), and/or alternative, open encryption techniques. 
     Accordingly, what is needed is a system and method which will allow cable operators to implement different compression and/or encryption techniques without upgrading multimedia receivers used by current subscribers. What is also needed is a system and method which will allow cable operators to seamlessly integrate more advanced compression and encryption techniques as those techniques are developed. 
     SUMMARY OF THE INVENTION 
     A method for efficiently transmitting several multimedia streams to one or more multimedia receivers comprises transmitting a first plurality of channels within a first plurality of frequency blocks having a first frequency range, said first frequency range being the range to which a legacy group of multimedia receivers are capable of tuning; and simulcasting said first plurality of channels within one or more alternate frequency blocks having an alternate frequency range, said alternate frequency range being the range to which an alternate group of multimedia receivers are capable of tuning. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A better understanding of the present invention can be obtained from the following detailed description in conjunction with the following drawings, in which: 
         FIG. 1  illustrates a prior art headend system for receiving and processing video content. 
         FIG. 2  illustrates a prior art multimedia receiver apparatus for receiving, decrypting and decoding cable/satellite channels. 
         FIG. 3  illustrates one embodiment of a system for storing and processing multiple broadcast multimedia streams. 
         FIG. 4  illustrates an embodiment of a system for storing and processing multiple broadcast multimedia streams wherein the streams are demultiplexed before being stored. 
         FIG. 5  illustrates more detail of an embodiment of a system for storing and processing multiple broadcast multimedia streams wherein the streams are demultiplexed before being stored. 
         FIG. 6  illustrates operation of one embodiment which employs a buffer of a specified duration. 
         FIG. 7  illustrates an embodiment in which a user may watch any program currently being broadcast from the beginning. 
         FIG. 8  illustrates a graphical user interface for selecting programs from a program guide and/or acquiring additional program-related information according to one embodiment of the invention. 
         FIG. 9  illustrates a wideband implementation according to one embodiment of the invention. 
         FIG. 10  illustrates operation of a conditional access module and a secure micro unit. 
         FIG. 11  illustrates a system for processing multiple multimedia streams and associated conditional access data. 
         FIG. 12  illustrates a timestamp index employed in one embodiment of the invention. 
         FIG. 13  illustrates techniques for identifying I-frames within a multimedia stream. 
         FIG. 14  illustrates operation of a fast forward function according to one embodiment of the invention. 
         FIG. 15  illustrates an embodiment witch includes one or more remote nodes for processing multimedia content. 
         FIG. 16  illustrates one embodiment of the invention for simulcasting channels in two or more encrypted formats. 
         FIG. 17  illustrates another embodiment of the invention for simulcasting channels in two or more encrypted formats. 
         FIG. 18  illustrates one embodiment of an apparatus for receiving and processing multimedia channels. 
         FIG. 19  illustrates an embodiment of the invention for digital signal simulcast which includes a mass storage device. 
         FIG. 20  illustrates another embodiment of the invention for digital signal simulcast which includes a mass storage device. 
         FIG. 21  illustrates an embodiment which transmits multimedia content over wider frequency blocks. 
         FIG. 22  illustrates an embodiment of a centralized uplink facility operable to receive video feeds from content providers, process the video feeds, and transmit the processed video feeds to headend systems. 
     
    
    
     DETAILED DESCRIPTION 
     In the following description, for the purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the present invention. It will be apparent, however, to one skilled in the art that the invention may be practiced without some of these specific details. In other instances, well-known structures and devices are shown in block diagram form to avoid obscuring the underlying principles of the invention. 
     Embodiments of a System and Method for Processing Multiple Broadcast Multimedia Streams 
     As illustrated in  FIG. 3 , one embodiment of the invention includes one or more tuners  320 ,  321  for receiving numerous statistically multiplexed streams within a specified frequency range and corresponding QAM and/or DPSK modules  330 ,  331  for demodulating the multiplexed streams. Unlike prior art systems, however, the system illustrated in  FIG. 3  transfers all of the statistically multiplexed multimedia content (or a subset thereof directly to multi-stream buffers  361 ,  362  on the mass storage device  360 . The buffers may be configured to store a specified duration of content (e.g., two hours) and/or a specified amount of content (e.g., 80 Gbytes). When a user selects a particular cable or satellite channel, the PID filter modules  340  and  341  (also referred to herein as a “PID depacketizer”) extract the multimedia packets for that channel (i.e., identified by the channel&#39;s PID codes) and reconstruct the underlying audio/video content by combining the packets in the proper order (i.e., the PID filter modules demultiplex and/or depacketize the content). One or more decoder modules  170  then decode the multimedia content using the appropriate decode/decompression algorithm (e.g., MPEG-2, MPEG-4, RealVideo® 8, Windows Media Technologies (“WMT”), . . . etc) and transmit the decoded multimedia content to a display  135  (e.g., a computer monitor or a television). 
     As mentioned above, if MPEG-2 is used as the compression algorithm, one set of multiplexed streams may have a combined bitrate approaching 40 Mbits/sec (or 16 Gbytes/hr); two sets, a combined bitrate of 80 Mbits/sec (or 32 Gbytes/hr) as indicated in  FIG. 3 . Accordingly, the mass storage device  360  of this embodiment is equipped with sufficient storage capacity and read-write bandwidth to store and process the multiplexed signal(s). More specifically, the mass storage device  360  in one embodiment is coupled to the system via an Ultra DMA-66/Ultra ATA-66 or faster interface (capable of supporting a throughput of at least 528 Mbits/sec), and has a storage capacity of 80 Mbytes or greater. It should be noted, however, that the particular interface type/speed and drive storage capacity is not pertinent to the underlying principles of the invention. For example, various different interfaces such as Small Computer System Interface (“SCSI”) may be used instead of the Ultra-ATA/Ultra DMA interface mentioned above, and various different drive capacities may be employed for storing the incoming digital content. 
     Storing content from multiple channels/streams on the mass storage device  360  in the foregoing manner provides numerous advantages over prior systems. More specifically, one embodiment of the invention uses the content stored in the multi-stream buffers  360 ,  361  to provide trick modes and other short term storage functions for all channels within the statistically-multiplexed group. For example, if a two-hour multi-stream buffer  361  is established, as indicated in the program guide  600  shown in  FIG. 6 , a user may pause any channel for up to two hours or rewind any channel back two hours (e.g., at 11:15 PM the user can rewind any channel back to 9:15 PM). Accordingly, if the user watching Program B on HBO East (PIDs  1 - 5  in the example) at 11:15, and decides to watch Program F from the beginning on the HBO Family channel (PIDs  11 - 15  in the example), and indicates so by choosing Program F via a remote control device or cursor control device, selection logic  350  will direct the PID filter module  340  to extract Program F from the multi-stream buffer  361 . In this manner, the user will be able to view Program F in its entirety even though the broadcast of Program F started approximately 1½ hours earlier. Similarly, users may select programs on any of the other channels (e.g., Program L on Cinemax® East) broadcast up to two hours earlier. It should be noted that a two-hour buffer is described above merely for the purpose of illustration. Various alternate buffer sizes may be employed while still complying with the underlying principles of the invention. 
     One embodiment of the invention demultiplexes the incoming multimedia streams before storing them to a multi-stream buffer on the mass storage device  460 . As illustrated in  FIG. 4 , this embodiment includes one or more multi-stream PID filter modules  440 ,  441  which extract the multimedia streams from the multiplexed signal and store them on the mass storage device  460  separated from one another. Thus, as illustrated in greater detail in  FIG. 5 , if the input to PID filter module  441  is a set of ‘n’ multiplexed streams, then the output will be ‘n’ independent, demultiplexed streams stored in a demultiplexed multi-stream buffer  502 . Storage buffers  445 ,  446  may be used by each of the multi-stream PID filters  440 ,  441 , respectively, to construct a portion of each stream (e.g., several Kbytes) before storing the portion to the mass storage device  460 . This will avoid excessive seeking of the mass storage device  460  (e.g., which would result if the storage device  460  were configured to write a small amount of data such as a single PID packet for each stream at a time). 
     Selection logic  550 , responsive to a user request to view a particular program (e.g., via remote control and/or cursor control device), will direct the decoder module  171  to read and decode one of the streams (i.e., the streams associated with PIDs  2 - 3  and  101 - 102  in the example) for rendering on a television or other display device  136 . The same operations may be performed on a separate group of ‘m’ multiplexed streams extracted by multi-stream PID filter module  440 . 
     As indicated in  FIG. 5 , each of the embodiments described herein may also employ a long term storage buffer  500  for recording programs specified by a user (e.g., similar to the long-term recording functionality of a VCR). In one embodiment, if a user selects a program for recording while the program is already in progress, the program content already stored in one of the demultiplexed multi-stream buffers will be transferred to the long term storage buffer  500  as well as any new program content. Alternatively, or in addition, the program content may simply be reclassified as long term storage content by changing the classification of its directory entry on the storage device rather than moving the content itself. 
     One benefit of separating the streams before storing them in the foregoing manner is that, in one embodiment, a user will be able to watch any program currently being broadcast from the beginning (i.e., the system will record back on each channel to the last complete program). Thus, as illustrated in the program guide  500  of  FIG. 7 , at 11:15 a user may watch program N on HBO Signature (PIDs  31 - 35  in the example) from the beginning even though the program started at 8:30. Similarly, the user may watch each of programs B, D, F, G, J and F from start to finish. 
     In one embodiment, a user may configure different buffer sizes for different channels. For example, a user who regularly watches a number of shows on HBO may decide to establish a large (e.g., 6 hour) buffer for that channel (e.g., by programming the system using a remote control, mouse or other cursor control device), whereas the same user may configure smaller buffers for channels which the user does not watch regularly (e.g., CSPAN). In one embodiment, the system will actively monitor the user&#39;s preferences and set larger buffer sizes based on which channels the user views the most frequently and/or the times/days during which the user views the channels. Various other buffer configuration schemes may be employed while still complying with the underlying principles of the invention. 
     It should be noted that various system functions described herein (e.g., the selection logic  350 ,  450 ,  550  used to select a particular multimedia stream; the PID filtering; the buffer settings; . . . etc) may be embodied in software executed by the CPU  125 . Alternatively, or in addition, these functions may be embodied in any combination of hardware (e.g., an application-specific integrated circuit (“ASIC”)), software and/or firmware while still complying with the underlying principles of the invention. 
     Using the improved buffering techniques described above, one embodiment of the invention provides users with a listing of all currently available programs from which they may select (e.g., those programs which may be viewed in their entirety). As illustrated in  FIG. 8 , one embodiment of the program listing is provided in the form of an interactive graphical user interface (“GUI”). The user may select a particular program listing by moving a highlight bar  803  through the listings using a cursor control device such as a remote control, keyboard or mouse. When the highlight bar  803  is highlighting the program entry which the user wishes to view, the user may select the program entry by clicking the enter key on the keyboard/remote or the select button on a mouse. 
     Each program entry in the particular embodiment illustrated in  FIG. 8  includes a video portion  800  and an informational portion  801 . The video portion in one embodiment is a thumbnail of the actual video content provided over the cable/satellite channel. For example, if the first entry in the program list shown in  FIG. 8  is HBO, then the video portion  800  of the entry will contain actual HBO video content. As a user moves through the various program entries, in one embodiment, the audio associated with that entry will also be generated. Moreover, in one embodiment, the system will display various types of user-specified broadcast content including, for example, live content (i.e., the program as it is currently being broadcast by HBO), recorded content (e.g., the first few minutes of the movie), or previews of the program (e.g., movie trailers). The underlying principles of the invention remain the same regardless of the type of content transmitted to the video portion  800  of the program entry. 
     Rendering audio/video content from each of the cable/satellite channels is simplified using embodiments of the present invention because the full set of multiplexed streams/channels are transmitted to the mass storage device and are accessible by the decoder modules  170 ,  171 . Such a configuration was not possible in prior systems which only transmit one or two de-multiplexed streams to the mass storage device and decoder modules. 
     In one embodiment, a selection region  805  will be provided for each program entry. If a user decides that he/she would like the program entry associated with the selection region  805  to be saved, the user may simply place a check mark (or other mark) in the selection region corresponding to that entry using a remote control or other cursor control device. The system will then store the program in long term storage and/or reclassify the content as long term content as described herein. If the embodiment shown in  FIG. 3  is employed, one embodiment of the invention will depacketize/demultiplex the selected program and save the program back to the mass storage device  360  (e.g., in either a packetized or a depacketized format). If the user does not wish to view the program immediately, this operation may be accomplished as a background task using the PID filters  340 ,  341  or other extraction software executed on the CPU  125 . 
     The information portion  801  of the program entry may include various types of program-related data including, for example, the title and year of the movie (if the program is a movie), program reviews, and/or actors in the program, to name a few. In one embodiment, the program-related data includes links to additional information. For example, the links may be network addresses such as uniform resource locators (“URLs”) which point to additional data stored on a network (e.g., the Internet). In response to a user selecting a URL (e.g., via a cursor control device), additional data addressed by the URL may be downloaded to the system and displayed to the user. Accordingly, this embodiment of the system is equipped with a modem or other device for providing two-way communication over the Internet or other network (e.g., the cable/satellite provider&#39;s network). Various types of modems may be employed including digital subscriber line (“DSL”) modems, cable modems, and plain old telephone system (“POTS”) dial up modems (i.e., depending on the particular type of communication channel used by the system). Of course, the type of modem used to support interactive communication is not pertinent to the underlying principles of the invention. 
     Wideband Implementations 
     In one embodiment of the invention, illustrated in  FIG. 9 , a wideband tuner  910  is configured in to lock on to several groups of multiplexed streams at once as opposed to just a single group. In the illustrated embodiment, the wideband tuner  910  is comprised of an analog-to-digital (“A/D”) converter  920  for receiving and digitizing numerous incoming streams—potentially all streams transmitted by a particular cable/satellite provider (e.g., over a 1 GHz frequency range); a multi-pass filter  930  which divides the digitized wideband signal into a plurality of discrete frequency bands (e.g., bands of 100 MHz); and a wideband QAM/DPSK module  935  which individually demodulates the content from each of the discrete frequency bands to reproduce all of the multiplexed multimedia streams. In one embodiment, the QAM/DPSK module  935  is comprised of a series of digital signal processors (“DSPs”) (e.g., one DSP per frequency band), each programmed with a QAM function for performing QAM demodulation and/or a DPSK function for performing DSPK demodulation. In addition, the DSPs may perform other functions such as signal equalization and noise filtering. In one embodiment, the DSPs operate under the control of the system&#39;s CPU  125  (e.g., the CPD executes software comprising the QAM/DPSK functions). 
     All of the groups of multiplexed streams (which, as indicated in  FIG. 9 , may include 500 or more PIDs), are transmitted through a wideband PID selector  940  which, in response to selection logic  450 , selects a subset of all the multiplexed PIDs for storage on the mass storage device  460 . The particular number of PIDs selected by the PID selector  940  may vary depending on the preferences of the user and/or the capabilities of the mass storage device  460  (e.g., the device&#39;s bandwidth and storage capacity). For example, in one embodiment, users may be prompted to select a set of “favorite” channels to be continually buffered on the mass storage device  460  (whereas the user&#39;s non-“favorite” channels will not be buffered, or will only be buffered for a limited time period). To support the increased storage and bandwidth requirements of the several sets of additional streams, one embodiment of the invention includes one or more additional mass storage devices (e.g., connected through a multi-drive high speed communication interface such as UDMA or SCSI). 
     In one embodiment, a PID demultiplexer  945  demultiplexes/depacketizes the streams selected by the wideband PID selector before storing them on the mass storage device  460 . Alternatively, or in addition, the streams may initially be stored in a multiplexed format on the mass storage device and the PID depacketizer  945  may extract PID packets only when a user decides to watch/record a particular program (e.g., as described above with respect to the embodiment shown in  FIG. 3 ). Once selected by a user, the stream is then transmitted through a decoder module  170  for MPEG-2 decoding (or other type of decoding, depending on how the stream was initially encoded) and to a display  135 . Although illustrated above as two separate modules, it will be appreciated that the functionality of the PID demultiplexer  945  and wideband PID selector  940  may be combined within a single module. 
     In one embodiment, a separate set of analog modules  911  may be included in the system to process and store legacy analog broadcasts. The analog components may include an analog tuners  902  for receiving the analog broadcast at a particular frequency, a decoder/digitizer module  904  for decoding and performing A/D conversion on the analog signal, and a compression module  906  for compressing the signal before storing it to the mass storage device  460 . 
     In one embodiment, the digital components may be configured to provide the analog functionality just described. For example, the DSPs within the QAM/DPSK module  935  may be programmed with an NTSC or PAL demodulation function for demodulating the incoming analog signal  901  (i.e., after the signal is digitized via the A/D converter). 
     Conditional Access Embodiments 
     In order to prevent users from viewing multimedia content which they do not have the right to view (e.g., subscription based channels, pay-per-view channels . . . etc) the multimedia content is frequently encrypted using a series of encryption keys before being transmitted. Accordingly, multimedia systems are generally equipped with conditional access (“CA”) subsystems for decrypting the incoming multimedia content. 
       FIG. 10  illustrates a CA module  1010  decrypting an incoming multimedia stream  1030  to produce a decrypted multimedia stream  1035 , which is then decoded by decoder  170  (e.g., using an MPEG-2 decoder) and rendered on a television display  135 . The decryption keys  1025  used to decrypt the multimedia content are transmitted to the CA module  1010  from a secure micro unit  1020 . Because the keys used to encrypt the multimedia stream typically change every few seconds, these key changes must be synchronized at the secure micro  1020  and CA modules  1010 . Accordingly a key selection data stream  1040  (also referred to herein as the “PID:CA” stream or “conditional access data”) is provided to the secure micro unit  1020  so that it knows precisely which key to transmit to the CA module  1010  at a given point in time. 
     As a result of the CA subsystem, if the incoming multimedia stream is stored in an encrypted format on a mass storage device, the decryption key changes associated with that multimedia stream must also be stored (i.e., so that when a user selects the stream, the secure micro will provide CA module with the decryption keys required to decrypt the stream). Prior systems deal with this problem simply by decrypting the multimedia stream before it is stored. However, storing decrypted content on a long term storage device in this manner leaves the copyright holder of the content exposed to unauthorized copying. In addition, because CA subsystems are typically only capable of decrypting one stream at a time, this configuration only provides for storage of only a single stream per CA module. 
     One embodiment of a system for concurrently processing decryption keys for multiple streams is illustrated in  FIG. 11 . Like prior embodiments, this embodiment includes one or more tuners  1020 ,  1021  for locking on to multimedia stream within a specified carrier frequency and one or more QAM and/or DPSK demodulators  1030 ,  1031  for demodulating the multimedia stream. 
     Unlike prior systems, however, the illustrated embodiment stores the PID:CA key selection data  1145  identifying the keys  1146  to be supplied by the secure micro  1160  to the CA modules  1170 ,  1171  for each multimedia stream, as well as timing data indicating the points in time at which each portion of the multimedia stream and associated key selection data  1145  were received/stored on the system (or alternatively, the points in time at which the stream/content was transmitted). When a user subsequently chooses a particular multimedia stream for playback, the secure micro  1160  uses the key selection data PID:CA  1145  for that stream to provide the correct series of keys to the CA modules  1170 ,  1171  for decryption of the selected stream. As in the embodiments described above, the user may be able to watch any program stored on the mass storage device for a predetermined buffer period or from the beginning (e.g., as described above with respect to  FIGS. 6 and 7 , respectively). In one embodiment, stream selection logic  1155  (embodied in hardware or software executed by the CPU  1185 ) will select the correct multimedia stream and PID:CA stream at the correct point in time (e.g., using techniques described in greater detail below) responsive to the user&#39;s selection (e.g., via a remote control or a cursor control device). Once the multimedia stream is decrypted by one of the CA modules  1170 ,  1171 , one or more decoder modules  1180  then decode the stream using an appropriate codec (e.g., MPEG-2) and transmit the decoded stream to a display  135 . 
     Identifying the correct points in time within the multimedia stream to begin playback is complicated by the fact that MPEG-2 data (as well as other types of encoded multimedia content) is not typically received by the system at a steady rate. For example, a portion of an MPEG-2 stream which contains significant movement between each of the image frames (e.g., a video of an explosion) will typically consume significantly more bandwidth than a portion of an MPEG-2 stream that contains little or no movement. Thus, as illustrated in  FIG. 12 , four 1-second portions ( 1211 ,  1212 ,  1213 ,  1214 ) of the incoming multimedia stream  1210  may occupy different amounts of space on the mass storage device. As such, in one embodiment of the system, an index of timing data  1200  is provided so that the stream selection logic  1155  can accurately locate where on the hard drive to start decrypting/rendering the multimedia stream in response to a user request to play back a particular program. Included within the index  1200  is a series of address pointers  1201 - 1204 , each associated with a timestamp (labeled 8:00:00 through 8:00:03). In operation, if a user selects a stored program which started at 8:00, for example, the stream selection logic  1155  will identify the 8:00:00 timestamp within the index  1200  and will start decrypting/playing the program stream back from the address identified by pointer  1201 . 
     In one embodiment, the stream selection logic  1155  will also identify the appropriate point within the PID:CA stream from which to read the necessary key changes. In one embodiment, a separate set of pointers to the PID:CA stream may be included within the timestamp index  1200  or, alternatively, within a separate PID:CA index (not shown). Alternatively, the conditional access data PID:CA may be stored directly within the index  1200 . However, in an embodiment in which the PID:CA stream is not encrypted and/or is transmitted at a steady rate (e.g., 1 Mbit/sec), address pointer entries to the PID:CA stream may not be required (i.e., the selection logic will be able to accurately identify where to read from the PID:CA stream without the need for an index). 
     In one embodiment, the timing index  1200  is transmitted along with the multiplexed multimedia streams in the form of an additional PID stream (e.g., a PID:INDEX stream transmitted from the head-end or uplink satellite that feeds the head-end). In other words, in this embodiment, the organization providing the source material (e.g., the cable or satellite provider) will generate and transmit the index to the end user&#39;s system. 
     However, if the content provider does not transmit the index, one embodiment of the system will construct the index  1200  as the multimedia streams are received and written to the mass storage device. For example, index/timestamp generation logic executed by the CPU  1185  (or embodied in hardware) may be configured to generate a new timestamp entry every 1/100 of a second and continuously store the results to the mass storage device  1140 . However, it should be noted that the particular frequency with which timestamp entries are generated is not pertinent to the underlying principles of the invention. 
     As illustrated in  FIG. 13 , an MPEG-2 stream  1310  is comprised of a series of I-frames separated by B-frames and P-frames. MPEG-2 uses similar DCT-based intraframe coding as the JPEG standard for each of the I-frames, but compresses the intervening video content by encoding only the differences between periodic I-frames within the B-frames and P-frames. Accordingly, it would be preferable if the pointers  1201 - 1204  contained in the timestamp index  1200  pointed to I-frames within the MPEG-2 stream rather than B or P frames (i.e., because the B and P frames are meaningless outside of the context of the two I-frames they connect). Accordingly, if the timestamp index is generated by the organization providing the source material, each of the pointers  1201 - 1204  should be selected to point to I-frames within the MPEG-2 stream. 
     If, however, the timestamp index  1200  is generated by the system, as described above, then the pointers  1201 - 1204  may not necessarily point to an I-frame. Accordingly, in one embodiment of the invention, if a stream is played back from an address pointer which does not point to an I-frame (e.g., such as pointer  1201  in  FIG. 13 ) then it will decrypt/decode the stream up until it reaches an I-frame and will begin playback from that point. For example, in  FIG. 13 , the system will begin decrypting the stream at the point identified by pointer  1201  (in the middle of B &amp; P frames  1302 ) but playback would not start until the decryption process reached I-frame  1303 . In one embodiment, the system identifies the I-frame  1303  by decrypting its I-frame header. 
     Similar techniques may also be employed to allow users to fast-forward through the multimedia content. More specifically, in response to a fast forward command, one embodiment of the system will display a series of I-frames in succession. Depending on the speed at which the fast forward is set to, this embodiment may jump several I-frames at once (as described in greater detail below). If the timestamp index described above contains pointers which point directly I-frames, then the I-frames will be identified directly via the index. 
     If, however, the index is constructed as the multimedia stream is received, then jumping from one I-frame to the next may not be entirely accurate because the number of B and P frames between each I-frame and the data contained within each B and P frame is not consistent. Accordingly, as illustrated in  FIG. 14 , when a user selects fast forward, one embodiment of the system will estimate the jump from the current I-frame  1301  to the next I-frame  1303  based on the speed of fast forward request and/or the estimated time between each I-frame. In one embodiment, the system will perform a lookup in the timestamp index  1200  to make the jump. Alternatively, or in addition, the jump may be based on the assumption that during standard playback, a new I-frame is decided approximately every ½ second. The underlying principles of the invention remain the same regardless of how the jump to the next I-frame is estimated. 
     Regardless of how the jump is estimated, once it occurs, one embodiment will then begin decrypting the stream using the decryption key data PID:CA  1145  associated with that point in time, until the decryption process reaches the desired I-frame  1303 . Once the I-frame  1303  is reached, it is decrypted, decoded and rendered on the display. The same techniques may then be employed for the estimated jump to the next I-frame  1305 . The system may identify each of the I-frames by decrypting their respective I-frame headers. 
     If one embodiment, if the jump lands in the middle of the next I-frame as illustrated in  FIG. 14  (as the jump from I-frame  1305  to  1307 , then one embodiment of the invention will decrypt the stream backwards until it reaches the beginning of I-frame  1307 . The system may identify the middle of an I-frame by the presence of I-frame data rather than B or P frame data (e.g., DCT intraframe data rather than inter-frame motion data). 
     If the speed of the fast forward request is set high enough the secure micro unit  1160  may be required to provide a new decryption key with each jump. Accordingly, one problem which may result is that the secure micro  1160  may not be capable of providing decryption keys to the CA module  1170  quickly enough (e.g., the secure micro may only be capable of supplying a new key every ⅓ second). If this is the case, then one embodiment of the invention will continue to display the current I-frame until a new key can be generated as it jumps over several I-frames at a time. In this manner, decryption will take place as quickly as the secure micro unit  1160  can generate new keys. 
     As the multimedia stream is decrypted during playback, one embodiment of the invention will store the decrypted stream back to the mass storage device  1140 , thereby replacing the encrypted multimedia data. At this time an I-frame index can be written to the storage device  1140  as well. Accordingly, if a user subsequently decides to rewind to a particular point within the multimedia stream, or decides to watch the program a second time, the foregoing I-frame identification techniques may no longer be required (i.e., because the stream will have been decrypted and an I-frame index may be available). In addition, in one embodiment, as soon as the user begins watching a particular multimedia stream, the system will run ahead of stream playback, decrypting the stream as quickly as it can (generally dictated by how quickly the secure micro unit  1160  can supply keys) and storing the decrypted stream back to the mass storage device. Using this technique an entire movie may be completely decrypted during the first several minutes of playback. Accordingly, if the user subsequently chooses to fast-forward through the movie, the I-frame identification techniques described above will not be required. 
     In one embodiment, any multimedia programs which the user designates for long term storage (e.g., by checking the selection region  805  corresponding to the program as illustrated in  FIG. 8 ), will be decrypted in the background by software executed on the CPU  1185  and/or using dedicated decryption hardware. This embodiment may be required in cases where the decryption keys provided by the cable/satellite provider expire after a predetermined period of time (i.e., and therefore could not be used to decrypt the multimedia programs after a predetermined time has elapsed). 
     In order to protect the copyright holders&#39; rights in the multimedia content stored on the mass storage device  1140 , one embodiment of the invention will employ additional encryption techniques once the multimedia content has been decrypted. For example, one embodiment of the system delivers a unique key to the mass storage device  1140  as soon as the system is powered up. This technique is available today on many current Ultra-ATA hard drives. If the wrong key is transmitted a predetermined number of times, the hard drive will render the data stored thereon inaccessible (e.g., in one embodiment the hard drive will format itself). Accordingly, an individual who steals the mass storage device  1140  will be unable to access the multimedia content. 
     In addition, in one embodiment, after the multimedia content is decrypted using keys supplied by the secure micro  1160 , one embodiment will re-encrypt the content using one or more known encryption algorithms. For example, in one embodiment, Data Encryption Standard (“DES”) encryption will be applied to the multimedia content before storing it back to the mass storage device  1141 . As is known in the art, DES is a NIST-standard secret key cryptography method that uses a 56-bit key. It will be appreciated, however, that various other encryption algorithms may be employed while still complying with the underlying principles of the invention. However, one benefit of using DES encryption is that many MPEG-2 decoder chips have the DES encryption function built in (e.g., such as the AViA-9600 from C-Cube Microsystems, Inc). As such, if the system is equipped with an MPEG-2 decoder, no additional hardware will be required, thereby reducing system costs. 
     In one embodiment, illustrated in  FIG. 15 , a network interface  1500  is configured in the system to provide communication to a remote multimedia node  1510  (also equipped with a network interface  1505 ). Various different networking protocols/standards, both wired (e.g., Ethernet) and wireless (e.g., 802.11b), be employed to support the communication between the various nodes. 
     The format in which multimedia content is transmitted to the multimedia node  1510  may depend on the node&#39;s capabilities. For example, in one embodiment, the node  1510  is equipped with its own conditional access module and secure micro unit (not shown). Accordingly, in this embodiment, multimedia streams requested by the remote node  1510  may be transmitted in an encrypted format along with the associated key selection data PID:CA. By contrast, in one embodiment the remote node  1510  may not be equipped with conditional access functionality. As such, in this embodiment, the multimedia content will be decrypted before being transmitted. In order to protect unauthorized access to the multimedia content (e.g., by an unauthorized user listening on the network), one embodiment will re-encrypt the stream before transmitting it to the remote node  1510  using an encryption format which the remote node can employ in real time (e.g., DES encryption). Various other techniques may be used to provide secure communication with the remote node  1510  while still complying with the underlying principles of the invention (e.g., communication may be encrypted using Secure Sockets Layer (“SSL”) encryption). 
     Embodiments of a System and Method for Multimedia Content Simulcast 
     In one embodiment of the invention, channels are transmitted from the headend using both standard encryption/compression (i.e., standard CA encryption and MPEG-2 compression) and non-standard encryption/compression (e.g., open encryption and MPEG-4 compression). Accordingly, using this embodiment, cable operators may design new multimedia receivers which take advantage of the more advanced encryption and/or compression techniques. At the same time, older multimedia receivers will still receive channels encrypted/compressed using standard encryption/compression. As such, cable operators may seamlessly migrate to the newer multimedia receivers over time (i.e., without incurring the significant cost associated with replacing all legacy multimedia receivers at once). 
     As illustrated in  FIG. 16 , one embodiment of a headend system  1600  for simultaneously broadcasting each digital multimedia stream (“simulcasting”) is comprised of a standard MPEG-2 module  1604  and conditional access module  1603  for transmitting digital streams to legacy multimedia receivers. In addition, the system  1600  includes one or more alternative compression modules  1601  for compressing the multimedia streams using non-MPEG-2 compression algorithms (e.g., MPEG-4, RealVideo 8, . . . etc) and/or one or more alternative encryption modules  1602  for encrypting the video content using non-standard encryption formats (e.g., Digital Video Broadcast (“DVB”) encryption, Secure Sockets Layer (“SSL”) encryption, DES encryption or any other encryption format). 
     In one particular embodiment, the alternative encryption modules  1601  encrypt all portions of the multimedia streams except for the I-frame header information, thereby providing an effective mechanism for identifying each I-frame within each multimedia stream stored on the mass storage device (e.g., to be used to jump backwards and forwards in the stream once it is stored in an encrypted format). A detailed description of alternate techniques for identifying I-frames within multimedia streams (i.e., if the I-frames are encrypted) is set forth above. 
     The headend system  1600  may also modify the initial compression format of the video streams. For example, one or more MPEG-2 decoder modules  1606  may decompress incoming MPEG-2 video streams. Alternative compression module(s)  1601  may then re-compress the video stream using one or more of the alternate compression formats. 
     As indicated by the dotted line connecting MPEG-2 compression module  1604  with alternate encryption module  1602 , in one embodiment of the invention, channels may be transmitted using standard MPEG-2 compression but alternate encryption. Similarly, as indicated by the line connecting alternate compression module  1601  with CA module  1603 , channels may be transmitted using standard encryption but alternate compression. Moreover, as indicated in  FIG. 16 , video streams which are received at the headend in a compressed format may be input directly to alternate encryption module  1602  for encryption. 
     Transmitting each digital video channel in two (or more) independent compression/encryption formats as described above will consume a significant amount of network bandwidth. As such, in the embodiment illustrated in  FIG. 16 , not all channels are simulcast. Rather, as indicated by bandwidth allocation  1620 , in this embodiment only the “premium” channels (e.g., subscription-based channels such as HBO, Showtime, Encore, Cinemax . . . etc) are simulcast, represented by allocation blocks  1626  and  1628 . The remainder of the digital and/or analog channels (i.e., the “basic” channels provided with any cable subscription) are transmitted in the clear as indicated by bandwidth allocation blocks  1622  and  1624 . Given the fact that analog channels are already transmitted unencrypted in most areas, transmitting the “basic” digital channels unencrypted will not expose cable companies to a significant amount of additional risk. 
     In order to further decrease the risk associated with transmitting unencrypted basic channels, in one embodiment, a subset of the basic channels are also simulcast as described above (i.e., using both standard and alternate encryption techniques). Thus, as indicated by the bandwidth allocation  1720  in  FIG. 17 , a selected group of basic digital channels are simulcast using both standard encryption (represented within allocation block  1726 ) and an alternative encryption (represented within allocation block  1728 ). The remaining basic digital channels are transmitted with no encryption, represented within bandwidth allocation block  1724 . Accordingly, using this embodiment, individuals attempting to illegally view or “pirate” cable channels will only be able to view a subset of the basic digital service, thereby further decreasing the risk to cable companies and the content providers. 
     In addition, in one embodiment, the channel line-ups in the simulcast and non-simulcast groups are continually modified. For example, a channel such as ESPN may be allocated to the unencrypted group some of the time and to the encrypted simulcast group the remainder of the time. In one embodiment, the channel allocation for each group is modified on a random basis. For example, after a predetermined period of time (e.g., every minute, hour, day . . . etc) a specified number of channels may be randomly allocated to the encrypted simulcast group, with the remainder being allocated to the unencrypted group. Randomly reallocating channels between groups in this manner makes it impossible for users to anticipate how the channels will be transmitted during any given period of time, thereby further decreasing the risk of pirating (i.e., without subscribing to the cable service, users will be unsure of the channels will be available from one day to the next). 
       FIG. 18  illustrates one embodiment of a multimedia receiver  1805  for receiving multimedia channels which have been transmitted using the techniques described above. As in prior embodiments, this embodiment includes a tuner  1810  for locking on to one or more channels and a QAM demodulator  1820  for demodulating the channels. Unlike standard cable systems, however, the illustrated embodiment includes a alternate decryption module  1830  for decrypting the channels which have been encrypted using non-standard encryption techniques (e.g., DVB encryption) and a decoder for decoding each of the channels using either standard decoding formats (e.g., MPEG-2) or alternate decoding formats (e.g., MPEG-4, Real Video 8 or any other compression technique employed at the headend  300  to encode/compress the channels). 
     The tuner  1810 , QAM module  1820 , alternate decryption module  1830 , decoder module  1850  and various other modules described herein may be implemented by hardware, software or any combination thereof. For example, in one embodiment, the tuner  1810 , QAM module  1820 , alternate decryption module  1830 , and/or decoder module  1850  are implemented using one or more application-specific integrated circuits (“ASICs”). 
     In one embodiment, illustrated in  FIG. 19 , the multimedia receiver  1905  is also equipped with a mass storage device  1140  for recording channels on behalf of the end user. Analog signals are initially converted to digital by an A/D converter module  1930 . An NTSC/PAL decoder module  1931  then decodes the underlying signal (i.e., according to the NTSC or PAL television standards), and a digital compression module  1932  compresses the digital signal before it is stored on the mass storage device  1140  (e.g., in MPEG-2, MPEG-4 or other compression format).  FIG. 20  illustrates an embodiment in which content is stored on the mass storage device  1140  in an encrypted format. The decryption module  1930  is employed to decrypt the content only after a particular program has been selected by the user. 
     Using the mass storage device  1140 , the multimedia receivers  1905 ,  2005  may employ any of the techniques described above for concurrently processing and storing multiple audio/video streams (see, e.g.,  FIGS. 3 through 9  and associated text). For example, the GUI illustrated in  FIG. 8  may be provided to allow users to select from a list of currently available programming, regardless of how the programming is transmitted to the multimedia receiver  1905 . In addition, embodiments of the multimedia receivers  1905 ,  2005  may store and process conditional access data as described above (see, e.g.,  FIG. 10 through 15  and associated text). For example, a timestamp index may be generated for those programs which are stored on the mass storage device  1140  in an encrypted format. 
     Various additional multimedia processing and storage techniques may be implemented in connection with the embodiments of the invention described herein. For example, the advanced compression techniques described in the co-pending application entitled “APPARATUS AND METHOD FOR INTELLIGENT MULTIMEDIA COMPRESSION AND DISTRIBUTION” (Ser. No. 09/721,556) may be employed (e.g., to modify the type of compression used for storing multimedia streams, to compress the streams in the background, . . . etc). This application is assigned to the assignee of the present application. 
     One benefit of transmitting multimedia channels using more advanced compression techniques such as MPEG-4 or Real Video 8 is that these techniques can achieve approximately 2 to 3 times the compression of MPEG-2 while maintaining a comparable level of video quality. As such, in one embodiment, a significantly greater number of channels may be transmitted in a single QAM signal. For example, if twelve MPEG-2 channels can be transmitted in a single 256 QAM, then 24 to 36 channels may be transmitted using the same QAM signal if more advanced compression techniques are used, resulting in a more efficient multimedia broadcast. Accordingly, multimedia receivers capable of decompressing the streams using more advanced decompression modules  1850 ,  1950 , will provide users with a greater number of channel selections per QAM demodulator  1820 ,  1920 , resulting in a less expensive multimedia receiver (i.e., because fewer QAM demodulators are needed) and/or an improved user experience (i.e., because a greater number of channels are available). 
     The standard PID packet size used by cable/satellite companies is 188 bytes. In one embodiment, when processing and storing multiple streams as described herein, packets for each stream are initially combined in memory. Once a sufficient number of PID packets have been combined in memory (e.g., 100 Kbytes), the combined chunk of data is written to the mass storage device  1140  all at once. Buffering and combining packets in this manner significantly reduces the seek time when writing the data out to disk (i.e., if the mass storage device  1140  is a hard drive). For example, if the PID packets were written to disk as soon as they were received, the disk head would spend in an inordinate amount of time jumping from one stream to the next, thereby significantly degrading system performance. 
     In one embodiment of the invention, the PID packet size is increased, thereby reducing the buffering requirements at the multimedia receiver. In other words, if each packet contains significantly more data than the current 188 bytes (e.g., 100 Kbytes) then the disk seeking problems described above will not be an issue. Each time the disk head seeks to write multimedia content from a particular stream, it will write for a significantly longer period of time before seeking to the next stream. Accordingly, the memory buffer may be configured to store fewer packets than the number of streams processed by the system. The new packet size may be equivalent to the combined “chunk” of data described above. In one embodiment, the new packet size is only employed for one of the simulcast digital channel groups (e.g., the one used for alternative compression/encryption techniques). 
     Rather than redefining the underlying PID packet size of 188 bytes, in one embodiment, standard 188-byte PID packets are combined at the headend and transmitted only after a predetermined number have accumulated for a particular stream. For example, the headend may wait to transmit data for a video stream until 500 PID packets for that stream have accumulated. 
     A larger packet size was not practical in prior systems because of the potential delay experienced when tuning from one stream to the next, particularly with respect to low-bandwidth streams. For example, a packet containing 100 Kbytes of data in a low bandwidth stream (e.g., an audio stream) may represent several seconds of playback. Accordingly, if a user tunes to that particular stream shortly after a packet has been received by the system, he/she may need to wait several seconds for the next packet to arrive. 
     Because embodiments of the present invention concurrently store and process multiple streams, however, if the user tunes to a low-bandwidth stream, playback may begin using portions of the stream buffered on the mass storage device  1140  (e.g., delayed from the live broadcast by a short amount of time, within which the next PID packet is received), In one embodiment, a minimum acceptable channel changing speed is established. If a delay greater than this minimum speed would result when tuning to a particular channel, then playback will begin from the portions of the stream stored on the mass storage device. In one embodiment, a synchronization option is provided which synchronizes the stream playback with the live broadcast, thereby allowing users to view/hear a non-delayed version of the stream (e.g., by waiting for the next PID packet to arrive before starting playback). 
     Various packet sizes may be employed while still complying with the underlying principles of the invention. However, in one particular embodiment, the packet size is selected based on how efficiently it may be written to the mass storage device. For example, based on the characteristics of the hard drive (e.g., seek time, block size, rotation speed, . . . etc) and the system (e.g., the number of concurrent streams being processed) a particular chunk of data may be the most efficient size for writing to the hard drive (e.g., 100 Kbytes). 
     In addition to the PID packet size limitations described above, current transmission systems are also limited to transmitting multimedia streams in legacy frequency bands, so that the streams can be processed by legacy receivers. For example, 64/256 QAM signals are typically transmitted within a plurality of 6 MHz frequency blocks. Tuners employed in current systems are configured to lock on to one of the 6 MHz frequency blocks and extract the underlying QAM signal. 
     In one embodiment of the invention, multimedia streams are transmitted using larger carrier frequency blocks (e.g., 30 MHz). One benefit of using larger blocks is that fewer (if any) guard bands are required to separate the blocks, thereby freeing up additional bandwidth (guard bands are required to separate each frequency block so that the boundaries for each block may be identified). In addition, if 24 to 36 channels may be transmitted per 6 MHz block using advanced compression (as described above) then more than 5 times this amount may be transmitted in a 30 MHz block, resulting in more than 120 to 144 channels per block (more than 5 times the number of channels may be transmitted because of the bandwidth freed up from the guard bands). 
     As illustrated in  FIG. 21 , in one embodiment, a high bandwidth tuner  2130  is employed to lock on to a frequency block which is wider than that typically used in cable systems. For example, if a 30 Mhz frequency block is designated, 144 (or more) channels may be transmitted within it, representing all of (or a significant portion of) the premium and/or basic digital channels transmitted over the cable network. As such, a high bandwidth tuner  2130  employed in this embodiment may be configured to lock on to the designated frequency block at all times. Because the tuner in this embodiment may only be required to lock to a single frequency band, it may be less expensive than a tuner capable of quickly jumping from one frequency block to the next, as used in prior systems, thereby further reducing system costs. 
     As indicated in  FIG. 21 , a separate tuner  2135  may also be configured to receive analog and digital channels transmitted over the 6 Mhz frequency blocks. As described above, analog streams may be processed by an A/D converter module  1930 , an NTSC/PAL decoder module  1931  and a digital compression module  1932 . However, in one embodiment, the analog channels may be digitally simulcast using alternate compression and/or encryption techniques and processed by the high bandwidth tuner  2130  along with the other digital content. As such, in this embodiment, a separate standard tuner  2135  may not be required (i.e., depending on the number of streams the high bandwidth tuner  2130  is capable of receiving). 
     As illustrated in  FIG. 22 , in one embodiment, a centralized uplink facility  2210  receives the video feeds directly from the content providers, processes the video feeds as described above, and transmits the processed video feeds to various headend systems  2221 - 2224 . For example, the centralized uplink facility  2210  may receive standard MPEG-2 video streams, decompress and recompress the video streams using MPEG-2 decompression modules and alternate compression modules, respectively, and simulcast the streams to the headend systems  2221 - 2224  in both MPEG2 compression and alternate compression formats (as described above with respect to the individual headend systems). Similarly, the centralized uplink facility  2210  may encrypt the streams using various alternate encryption techniques described above before transmitting the streams to the headend systems  2221 - 2224 . 
     Processing video streams at a centralized point within the cable network will reduce the equipment cost at each headend, thereby significantly reducing costs for the entire network. For example, if MPEG-2 video streams are converted to an alternative compression format at the centralized uplink facility, then separate MPEG-2 decoder modules will not be required at each individual headend. Similarly, if alternative encryption is performed at the centralized uplink facility, then separate alternate encryption modules will be required at each headend. 
     While only a single centralized uplink facility  2210  is illustrated in  FIG. 22 , two or more centralized uplink facilities  2210  may be configured to process video streams for two or more specified groups of headends. Moreover, although communication between the centralized uplink facility  2210  and the headends illustrated in  FIG. 22  is provided via satellite  2230 , it should be noted that various other configurations are contemplated within the scope of the present invention. For example, certain headends may communicate with the centralized uplink facility  2210  via wired network channels (e.g., fiber optic cable) as well as alternate wireless channels (e.g., radio frequency broadcast channels). 
     Embodiments of the invention may include various steps, which have been described above. The steps may be embodied in machine-executable instructions which may be used to cause a general-purpose or special-purpose processor to perform the steps. Alternatively, these steps may be performed by specific hardware components that contain hardwired logic for performing the steps, or by any combination of programmed computer components and custom hardware components. 
     Elements of the present invention may also be provided as a computer program product which may include a machine-readable medium having stored thereon instructions which may be used to program a computer (or other electronic device) to perform a process. The machine-readable medium may include, but is not limited to, floppy diskettes, optical disks, CD-ROMs, and magneto-optical disks, ROMs, RAMs, EPROMs, EEPROMs, magnet or optical cards, propagation media or other type of media/machine-readable medium suitable for storing electronic instructions. For example, the present invention may be downloaded as a computer program product, wherein the program may be transferred from a remote computer (e.g., a server) to a requesting computer (e.g., a client) by way of data signals embodied in a carrier wave or other propagation medium via a communication link (e.g., a modem or network connection). 
     Throughout this detailed description, for the purposes of explanation, numerous specific details were set forth in order to provide a thorough understanding of the present invention. It will be apparent, however, to one skilled in the art that the system and method may be practiced without some of these specific details. For example, while the embodiments described above focused on specific frequency blocks for implementing aspects of the present invention (e.g., 30 MHz), various other frequency block sizes may be employed. Similarly, while specific encryption and compression types were described above (e.g., MPEG-4, Real Video 8, DES encryption, . . . etc) various other encryption and/or compression algorithms may be employed while still complying with the underlying principles of the invention. 
     In other instances, well known structures and functions were not described in elaborate detail in order to avoid obscuring the subject matter of the present invention. For example, although not illustrated, it will be appreciated that various levels of buffering may be included in the embodiments described herein. For example, in the embodiment illustrated in  FIG. 11 , buffers (e.g., SDRAM, RDRAM, . . . etc) may be configured between the QAM/DPSK modules  1130 ,  1131  and the mass storage device  1140  and/or between the mass storage device  1140  and the PID filters  1150 ,  1151 . In fact, buffers may be provided in this manner between any of the system modules in order to improve system performance. The buffers may be separate, independent modules and/or may be assigned blocks of addressable space within a single unified memory (e.g., a RAM module shared between the CPU  1185  and other system components). The underlying principles of the invention remain the same regardless of which types of buffers are used. 
     For the foregoing reasons, the scope and spirit of the invention should be judged in terms of the claims which follow.