Patent Publication Number: US-9426335-B2

Title: Preserving synchronized playout of auxiliary audio transmission

Description:
CROSS-REFERENCE TO RELATED PATENT APPLICATIONS 
     This patent application is a continuation of U.S. patent application Ser. No. 12/715,481, filed Mar. 2, 2010, the disclosure of which is incorporated herein, in its entirety, by reference. 
    
    
     TECHNICAL FIELD 
     The present disclosure relates generally to audio and video (A/V) stream synchronization. 
     BACKGROUND 
     A growing number of consumers now have high speed, or broadband, connections to the Internet in their homes. The increased bandwidth provided by these broadband connections allows the delivery of digital television, video, and multimedia services to customer premises (e.g., home or business consumers). These services are transported over a network as audio and video (A/V) streams. At the customer premises, a digital receiver, set-top box, or computer, among other devices, decodes the A/V streams and generates a picture signal with associated sound for presentation by a television or monitor with audio-play functionality. A switch to a different A/V stream (e.g., via channel change, or other stream transition event) results in a finite amount of delay before the new A/V stream can be decoded and presented in synchronization. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Many aspects of the disclosure can be better understood with reference to the following drawings. The components in the drawings are not necessarily to scale, emphasis instead being placed upon clearly illustrating the principles of the present disclosure. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the several views. 
         FIG. 1  is a block diagram that illustrates an example environment in which certain embodiments of audio-video-pacing (AVP) systems and methods can be implemented. 
         FIG. 2  is a block diagram that illustrates an embodiment of an example audio-video (A/V) source of an example AVP system. 
         FIG. 3  is a block diagram that illustrates an embodiment of an example receive-and-process (RP) system of an example AVP system. 
         FIG. 4  is a schematic diagram that illustrates an example of A/V pacing responsive to a stream transition event in an example AVP system. 
         FIG. 5  is a schematic diagram that illustrates an example of buffer expansion in an example AVP system. 
         FIG. 6  is a flow diagram that illustrates an embodiment of an AVP method implemented at a downstream network device of an example AVP system. 
         FIG. 7  is a flow diagram that illustrates an embodiment of an AVP method implemented at an upstream network device of an example AVP system. 
         FIG. 8  is a flow diagram that illustrates an embodiment of a buffer expansion/contraction method implemented at a downstream network device of an example AVP system. 
         FIG. 9  is a flow diagram that illustrates an embodiment of a buffer expansion/contraction method implemented at an upstream network device of an example AVP system. 
     
    
    
     DESCRIPTION OF EXAMPLE EMBODIMENTS 
     Overview 
     In one method embodiment, providing by a network device a multiplex of compressed versions of a first video stream and a first audio stream, each corresponding to an audiovisual (A/V) program, the first video stream and the first audio stream each corresponding to a first playout rate and un-synchronized with each other for an initial playout portion; and providing a compressed version of a second audio stream, the second audio stream corresponding to a pitch-preserving, second playout rate different than the first playout rate, the second audio stream synchronized to the initial playout portion of the first video stream when the first video stream is played out at the second playout rate, the first audio stream replaceable by the second audio stream for the initial playout portion. 
     Example Embodiments 
     Disclosed herein are various example embodiments of audio-video pacing (AVP) systems and methods (collectively, AVP system or AVP systems) in a communications environment, such as a subscriber television system, that provides for synchronous A/V presentation without delay responsive to a stream transition event (e.g., channel change, trick modes, etc.). Some embodiments of the AVP system provide for buffer expansion and/or contraction while maintaining the A/V presentation in a synchronous and uninterrupted fashion. 
     In one stream transition event embodiment, an A/V source (e.g., headend encoder) or a channel change server (each also referred to herein as an upstream network device) generates (or receives) a pitch-constant (pitch-preserving, pitch-preserved, or the like), paced-down (slowed-down) audio track, the pitch-preserving audio corresponding to a portion of an audiovisual program. The audiovisual program and pitch-preserving audio are processed and delivered to a receive-and-process (RP) system (also referred to herein as a downstream network device), such as a set-top terminal, computer, etc., in response to, for instance, a channel change event requested by the RP system. The pitch-preserving audio may be sent in a multiplex of compressed video and audio streams (e.g., the multiplex, or transport stream, comprising a single program or multiple program transport stream), or in some embodiments, in association with a stream that is separate from the multiplex stream (e.g., delivered via a unicast transmission). The RP system receives the pitch-preserving audio track contemporaneously with the video stream of the multiplex, and decoding logic of the RP system slows down the video decoding clock rate to a decoding rate that equals the decoding rate of the pitch-preserving audio track. The RP system decodes the video and pitch-preserving audio, and plays out the decoded video stream in synchronization (e.g., lip-synched) with the decoded, pitch-preserving audio track, circumventing the audio-video presentation delay typically associated with audio-video transmissions while preserving the sound quality as perceived by a user in uninterrupted fashion. Presentation of the real-time audio associated with the multiplex is delayed at least until the real-time audio “catches up” (e.g., timestamp values match) to the video. 
     In one buffer expansion embodiment, an upstream network device provides one or more selectable, pitch-preserving audio tracks for playout with video of, for instance, a multiplex of real-time video and audio. The playout of the appropriate pitch preserving audio is synchronized with the video, the video played-out at a decoding rate that is slower than the real-time video of the multiplex. The one or more pitch-preserving audio tracks may be delivered (e.g., via the multiplex or as a separate unicast or multicast stream) in response to a request by an RP system. In one embodiment, the RP system comprises logic to determine the need for buffer expansion (e.g., to satisfy forward error correction (FEC) block or retransmission buffer re-sizing requirements). The substitution or replacement for decoding and presentation of real-time audio of the received multiplex with the pitch-preserving audio tracks results in an increase (e.g., incremental) in buffer size without disturbing, or at least mitigating the disturbance, of a user&#39;s viewing experience. Responsive to obtaining a suitable or targeted buffering level, decoding logic of the RP system plays-out the video at the real-time decoding rate in synchronization with real-time audio. 
     These and other embodiments and/or other features are described hereinafter in the context of an example subscriber television system environment, with the understanding that other multimedia (e.g., video, graphics, audio, and/or data, collectively or individually also referred to herein as media content) environments may also benefit from certain embodiments of the AVP systems and methods and hence are contemplated to be within the scope of the disclosure. It should be understood by one having ordinary skill in the art that, though specifics for one or more embodiments are disclosed herein, such specifics as described are not necessarily part of every embodiment. 
       FIG. 1  is a block diagram of an example environment, a subscriber television system or network  100 , in which certain embodiments of AVP systems and/or methods may be implemented. It should be understood by one having ordinary skill in the art, in the context of the present disclosure, that the subscriber television network  100  shown in  FIG. 1  is merely illustrative, and should not be construed as implying any limitations upon the scope of the disclosure. The subscriber television network  100  includes a headend  101  comprising one or more audio-video (A/V) sources  102  and one or more channel change servers  104  (one shown) communicatively coupled to one or more customer premises  108  over a communications network  106 . The A/V sources  102  deliver various digital services (e.g., borne from local feeds or storage, and/or sourced via a provider network upstream of the headend  101  and processed at the headend  101 ) to subscribers, which may include broadcast television programming, video-on-demand (VoD), pay-per-view, music, Internet access, e-commerce (e.g., online shopping), voice-over-IP (VoIP), and/or other telephone or data services. In one embodiment, the A/V sources  102  comprise pitch-preserving audio logic (explained further below) configured to generate pitch-preserving audio tracks for portions of A/V programming. In some embodiments, pitch-preserving audio tracks are delivered from one or more sources upstream of the A/V sources  102 , or generated elsewhere in the network  100 . The A/V sources  102  comprise, in some embodiments, codec and encryption/decryption functionality (explained further below), and are configured to deliver encoded (e.g., according to one or more of a plurality of different transport and video and/or audio coding standards/specifications, such as AVC, MPEG-2, MP3, etc.) video, audio, data, and/or graphics content for a single program carried in a single program transport stream (e.g., MPEG-2, which includes one or more packetized elementary stream (PES) packet streams sharing a common time base), and in other implementations, the encoded visual content for multiple programs may be carried as multiple MPEG-2 programs (multiple program transport stream), each MPEG-2 program associated with its own respective time base. Accordingly, the multiplex of media content for a given program or programs may be transported as a transport stream, the transport stream delivered with or without further encapsulation (e.g., Real-time Transport Protocol (RTP)/User Datagram Protocol (UDP)/Internet protocol (IP), UDP/IP, etc.). As shown, the channel change server  104  receives encoded streams from the A/V sources  102  and buffers the same for a defined period of time (e.g., last defined portion of programming for each channel) to provide error recovery (e.g., retransmission) and/or accelerated channel change capabilities. 
     It should be understood that, although MPEG-2 based video encoding and transport is described throughout the disclosure, encoding and/or transport according to other video and/or audio specifications and/or standards (including proprietary mechanisms) may similarly benefit from the AVP systems described herein and hence are contemplated to be within the scope of the disclosure. 
     In one embodiment, shown in  FIG. 1 , the A/V sources  102  and channel change server  104  are co-located at the headend  101 , though it should be understood by one having ordinary skill in the art that such co-location may be at other locations in the network  100  (e.g., hub, node, etc.). In one embodiment, the A/V sources  102  and channel change server  104  are coupled to one another via a local area network (e.g., an Ethernet network). In some embodiments, A/V sources  102  and channel change server  104  may be located in separate locations. 
     The customer premises  108  each comprise one or more receive-and-process (RP) systems  110  (one per premise shown) and one or more display devices, such as display device  112 . The display device  112  is coupled to, or in some embodiments, integrated with, the RP system  110 . In one implementation, the display device  112  is configured with an audio component (e.g., speakers), whereas in some implementations, audio functionality may be provided by a device that is separate from, yet communicatively coupled to, the display device  112  and/or RP system  110 . The RP system  110  further includes pacing logic  114  and buffer management (BM) logic  116 . The pacing logic  114 , in cooperation with decoding logic of the RP system  110 , includes functionality to effect substitution of real-time audio received in a multiplex with pitch-preserving audio tracks. The buffer management logic  116 , in cooperation with the pacing logic  114 , facilitates buffer management by effecting buffer contraction and/or expansion based on user or resident application requirements. Both of these modules are described further below. The RP system  110  (also referred to herein as a digital receiver or processing device) may comprise one of many devices or a combination of devices, such as a set-top box, television with communication capabilities, mobile devices such as cellular phone, personal digital assistant (PDA), or other computer or computer-based device or system, such as a laptop, personal computer, DVD and/or CD recorder, among others. 
     The communications network  106  comprises a bi-directional network, or, in some embodiments, a one-way network, and may include a cable television network, a satellite television network, a terrestrial network, an IP network, or a combination of two or more of these networks or other networks. Further, network PVR and switched digital video are also considered within the scope of the disclosure. Generally, the communications network  106  may comprise a single network, or a combination of networks (e.g., local and/or wide area networks). For instance, the communications network  106  may comprise a wired connection or a wireless connection (e.g., satellite, wireless local area network (LAN), etc.), or a combination of both. In the case of wired implementations, communications network  106  may comprise a hybrid-fiber coaxial (HFC) medium, coaxial, optical, twisted pair, etc. Other networks are contemplated to be within the scope of the disclosure, including networks that use packets incorporated with and/or compliant to other transport protocols or standards or specifications. 
     It should be understood by one having ordinary skill in the art, in the context of the present disclosure, that the subscriber television network  100  may comprise additional equipment and/or facilities, such as one or more other servers, routers, and/or switches at one or more locations of the network  100  that process, deliver, and/or forward (e.g., route) various digital (and analog) services to subscribers. In some embodiments, the subscriber television network  100  (or components thereof) may further comprise additional components or facilities, such as QAM and/or QPSK modulators, routers, bridges, Internet Service Provider (ISP) facility servers, private servers, on-demand servers, multimedia messaging servers, program guide servers, gateways, multiplexers, and/or transmitters, among other equipment, components, and/or devices well-known to those having ordinary skill in the art. 
     In one embodiment, the components of an AVP system comprise the A/V source  102 , channel change server  104 , or the RP system  110 , individually (or select components thereof), or in some embodiments, as a collection of two or more of these components and/or others shown (or not shown) in  FIG. 1 . 
       FIG. 2  is a block diagram that illustrates an embodiment of an example A/V source  102 , though the same or similar components may also be found in certain embodiments of the channel change server  104 . It should be understood by one having ordinary skill in the art, in the context of the present disclosure, that the A/V source  102  shown in  FIG. 2  is merely illustrative, and should not be construed as implying any limitations upon the scope of the disclosure. The A/V source  102  comprises a memory  202  that comprises a tangible medium such as volatile memory (e.g., random access memory (RAM)) and/or non-volatile memory (e.g., read-only memory (ROM)), the memory  202  encoded with various instructions or executable code. The A/V source  102  further comprises an optional storage device  204  (e.g., CD, DVD, etc.), a processor  206  (e.g., microcontroller, microprocessor, digital signal processor, etc.), and a network interface  208  configured to enable the reception of uncompressed or compressed A/V streams (or other media content streams) from a network provider or other devices, and further configured to provide processed (e.g., encrypted, encoded, etc.) A/V streams to other components (e.g., channel change server  104 ) or devices in the network  100 . The memory  202 , storage device  204 , processor  206 , and network interface  208  are coupled over a bus  210 . 
     In one embodiment, the memory  202  comprises codec logic (codec)  212 , pitch logic  214 , and encryption (encrypt) logic  216 . Though shown as software, it should be understood that functionality of one or more of the codec logic  212 , pitch logic  214 , and encryption logic  216  may be implemented in some embodiments in hardware, or a combination of hardware and software. The encryption logic  216  may further comprise decryption logic (not shown) in some embodiments. The codec logic  212  is configured to receive and process uncompressed A/V streams associated with an A/V program. In some embodiments, the codec  212  includes transcoding functionality. 
     The pitch logic  214 , in cooperation with the codec logic  212 , is configured to generate audio tracks (e.g., of predetermined, discrete interval or segment lengths) based on the decoded A/V streams, the audio tracks generated at one or more selectable (or fixed in some embodiments) decoding rates that are incrementally slower, or faster, than the intended presentation rate (e.g., original or real-time playout rate, referred to herein also as the 1× rate). For instance, one track may be a pitch-preserving, paced-down (e.g., at 80% of the original rate, or 0.8×) audio track, another track for the same playout portion at 0.9×, etc. In some implementations, paced-up (sped-up), pitch-preserving audio tracks may be generated (e.g., 1.1×). The factor of playout rate relative to the original playout rate is based on one or more factors, such as the targeted amount of buffer expansion/contraction, effect on viewer experience, among other factors. In some embodiments, the audio tracks are provided upstream of the A/V source  102 . 
     The pitch logic  214 , in cooperation with the codec logic  212 , is configured to determine locations (e.g., associated with random access points or RAPs) in decoded A/V streams where substitution of real-time audio segments or intervals with the pitch-preserving audio tracks will go un-noticed or relatively un-noticed by a viewer. In one embodiment, locations in a given A/V presentation are selected for substitution based on what is occurring, in a programming presentation, in the audio domain (e.g., the nature of the audio, such as whether it is rhythmic, silent, etc., whether the audio is concert quality music or hard rock, noise, etc.) and/or video domain (e.g., still scene, presence of significant motion, etc.) at that location(s), and whether substitution at the given location(s) results in a good choice, or at least, an acceptable choice. In one embodiment, the pitch logic  214  is configured to generate optional auxiliary data that, when delivered over the communications network  106 , assists downstream network devices in determining which packets (e.g., via packet identifiers) of 1× audio to replace with pitch-preserving audio (e.g., 0.8× audio). 
     Explaining further, headend equipment generally delays audio with respect to video, which results in a time offset between real-time audio and video streams at the time the real-time streams are received by the RP system  110 . The pitch logic  214  is configured to produce pitch-preserving audio streams from the original audio stream (e.g., in real-time), and thus the time offset (and any further processing delay) is a remnant from processing of the original streams that should be addressed to achieve A/V synchronized playout at the RP system  110 . In one embodiment, the pitch logic  214  (or an extension thereof) compensates for any time offset by delaying (e.g., via buffering mechanisms) the video stream with respect to the pitch-preserving audio stream to enable a synchronous (or near synchronous) output of the video stream and corresponding pitch-preserving audio stream. In some embodiments, such a compensating delay between a video stream and corresponding pitch-preserving audio stream may be imposed at other components (hardware and/or software) or devices, such as a multiplexer (not shown) or at the channel change server  104 . In the latter implementation of the channel change server  104  (which is configured to buffer video and audio streams for unicast bursts), the channel change server  104  may choose an appropriate starting point for the pitch-preserving audio streams based on the starting point of the unicast burst. In some embodiments, other mechanisms may be employed to impose such compensating delays. 
     Note that optional forward error correction (FEC) coding may also be implemented at the A/V source  102  or channel change server  104  according to known manner. 
     The codec logic  212  codes the audio track (and corresponding video) according to a given coding specification and/or standard (e.g., MPEG-2, AVC, etc.), and the encryption logic  216  encrypts the coded content. The coded and encrypted video and audio (and other data) streams may undergo further processing in known manner, such as multiplexing as a single program or multiple program transport stream, optional encapsulation (e.g., RTP/UDP/IP, UDP/IP, etc.), modulation (e.g., QAM modulation), among other processes as is applicable for the given system environment, and delivery to customer premises  108 . 
     In one embodiment, the processed (e.g., coded and encrypted), pitch-preserving audio is delivered over the communications network  106  multiplexed in the original MPEG-2 transport stream (the original MPEG-2 transport stream delivered over the network  106  with or without further encapsulation). Processing on the downstream network device side is described below in association with the RP system  110 . 
     In some embodiments, the pitch-preserving audio is delivered to the channel change server  104 , from which the pitch-preserving audio is delivered to the customer premises  108 . For instance, the channel change server  104  receives from the A/V source  102  the processed, pitch-preserving audio multiplexed in the original MPEG-2 transport stream. As another example embodiment, the channel change server  104  receives the processed, pitch-preserving audio multiplexed in an MPEG-2 transport stream encapsulated in a separate RTP stream, with appropriate management of the program clock reference (PCR)/presentation timestamp (PTS) information among the original transport stream and the separate RTP stream. In either case, the pitch-preserved audio is delivered from the channel change server  104  via an RTP session responsive to a stream transition event or as requested by the RP system  110 , with appropriate timing established at the channel change server  104  between the transport stream and the RTP stream. In some embodiments, a digital control manager may be an intervening component that uses SSRC multiplexing with the original RTP stream. In embodiments where transport-level synchronization is unavailable or otherwise unsuited for the application, RTP-level synchronization may be employed in known manner. 
     In certain embodiments using the channel change server  104  for delivery of the pitch-preserving audio, delivery may be implemented via a unicast retransmission session with payload-type multiplexing. Additionally, note that in buffer management implementations, the channel change server  104  may provide the segmented pitch-preserving audio on a separate multicast session, whereby the RP systems  110  join and extract as needed and leave the multicast session when convenient. 
     As indicated above, one or more of the functionality shown in, or described in association with, the A/V source  102  of  FIG. 2  may also reside in the channel change server  104 , thus enabling generation of the pitch-preserving audio at the channel change server  104 . In such embodiments, the channel change server  104  may receive decryption keys from the A/V source  102 , and parse, extract, decrypt, and decode the transport stream comprising the coded and encrypted 1× video and audio (and other data) received from the A/V source  102  (or from other sources). In some embodiments, the channel change server  104  retains as much audio in a buffer as is stored of the transport stream as a whole to enable a time-window into the encrypted audio. 
     Pitch logic  214  in cooperation with the codec logic  212 , both residing in the channel change server  104 , employ a proactive approach, an on-demand approach, or a combination of both approaches in the generation of the pitch-preserving audio. In the proactive approach, the pitch logic  214 , in cooperation with the codec logic  212 , operates similarly as described above as occurring at the A/V source  102 , which essentially amounts to picking an appropriate RAP (e.g., without “prompting” or demand), generating the pitch-preserving audio track based on conditions in the audio and/or video domain for the particular location of the audiovisual programming selected, and retaining the pitch-preserving audio stream for implementation responsive to a stream transition event or RP system request. 
     In the on-demand approach, the channel change server  104  awaits a request from the RP system  110 , and responsive to the request, selects an appropriate RAP from which to provide a burst stream, generates the pitch-preserving audio, and provides the pitch-preserving audio as an alternative elementary stream to the RP system  110 . The request may be based on one of several mechanisms, with or without modification, such as a rapid channel change (RAMS), a retransmission (NACK), codec control message (e.g., as in RFC  5104 ), among other forms of feedback or messages. The RP system  110  inserts the pitch-preserving audio in an audio decode buffer in place of the 1× audio. In some embodiments, the channel change server  104  processes pitch-preserving audio in an on-going manner (e.g., over a few groups of pictures (GoPs) or other defined intervals), terminating the extract and pitch-preserving audio generation in one embodiment responsive to a timeout without any further requests. This terminable, on-going process over the defined interval enables picking up of an impulse of channel changes for a given channel, while avoiding overloading the channel change server  104  with continuous audio processing. 
     One or more of the above-mentioned software logic (e.g.,  212 ,  214 , and/or  216 ) may be combined with each other as a single module in some embodiments, or distributed among different devices in some embodiments. The upstream network device software logic (e.g.,  212 ,  214 , and/or  216 ) comprise instructions that, when executed by the processor  206 , cause the processor  206  to perform the various functions associated with the A/V source  102  and/or channel change server  104 . In some embodiments, functionality of one or more of the upstream network device software logic (e.g.,  212 ,  214 , and/or  216 ) may be implemented at least in part via fixed or programmable logic, such as an integrated circuit or field programmable gate array (FPGA), among others. 
       FIG. 3  is a block diagram that illustrates an embodiment of an example RP system  110 . It should be understood by one having ordinary skill in the art, in the context of the present disclosure, that the RP system  110  shown in  FIG. 3  is merely illustrative, and should not be construed as implying any limitations upon the scope of the disclosure. The RP system  110  includes a communication interface  302  (e.g., depending on the implementation, suitable for enabling communication functionality for in-band and/or out-of-band transport streams or encapsulated transport streams (herein, in-band transport stream also referred to as a multiplex). For instance, the communication interface  302  may be of a type suitable for communication over an IP network, a coaxial cable network, an HFC network, and/or wireless network, among others. The communication interface  302  is coupled to a demultiplexer (herein, also demux)  304 . The demux  304  is configured to identify and extract information in the video and audio streams (e.g., transport stream) to facilitate the identification, extraction, and processing of the compressed pictures and associated audio. Such information may include Program Specific Information (PSI) (e.g., Program Map Table (PMT), Program Association Table (PAT), etc.) and parameters or syntactic elements (e.g., Program Clock Reference (PCR), timestamp information, payload_unit_start_indicator, etc.) of the transport stream (including packetized elementary stream (PES) packet information). Such information is forwarded to or otherwise received by the pacing logic  114  and bandwidth management logic  116  and/or media engine  306  as explained further below. In one embodiment, the demux  304  is configured with programmable hardware (e.g., PES packet filters). In some embodiments, the demux  304  is configured in software, or a combination of hardware and software. 
     Although the RP system  110  is described in the context of an IPTV implementation, it should be appreciated by one having ordinary skill in the art that the RP system  110  may comprise additional and/or different components in some embodiments. For instance, some embodiments of the RP system  110  may include a tuner system (e.g., radio frequency tuning, not shown) coupled to the communication interface  302 , the tuner system comprising one or more tuners for receiving the transport streams received via the communication interface  302 . Further, in some embodiments, a demodulator may be employed, such as to demodulate the received carrier signal, wherein the demux  304  is configured to parse the transport stream packets of one or more defined carrier frequencies. 
     The demux  304  is coupled to a bus  305  and to a media engine  306  (also known as an audio/video (a/v) processing or decoding device). The media engine  306  comprises, in one embodiment, decoding logic comprising one or more of a respective audio decoder  308  and video decoder  310 . The decoding logic is further configured by the pacing logic  114  to substitute 1× audio with pitch-preserving audio and vice versa. The decoding logic is further configured by the buffer management logic  116  to determine a need for buffer expansion or contraction, and generate feedback requests (e.g., RTP Control Protocol, or RTCP, among others) to an upstream network device for pitch-preserving audio. Though shown as a software module in memory  322 , the pacing logic  114  and/or buffer management logic  116  may reside elsewhere in RP system  110 , alone or integral to other components, such as the media engine  306  or elsewhere in the RP system  110 , and hence may also be referred to herein as part of the decoding logic in some embodiments. The media engine  306  is further coupled to the bus  305  and to media memory  312 , which in one embodiment comprises one or more buffers for temporarily storing compressed and/or reconstructed pictures, such as video decoder buffer (VDB)  340  and audio decoder buffer (ADB)  342 . In some embodiments, the buffers  340 ,  342  of the media memory  312  may reside in other memory (e.g., memory  322 , explained below). 
     The RP system  110  comprises additional components coupled to bus  305 . For instance, the RP system  110  further comprises a receiver  314  configured to receive user input (e.g., via direct-physical or wireless connection via a keyboard, remote control, voice activation, etc.) to convey a user&#39;s request or command (e.g., for program selection, stream manipulation such as fast forward, rewind, pause, channel change, etc.), one or more processors (one shown)  316  for controlling operations of the RP system  110 , and a clock circuit  318  comprising phase and/or frequency locked-loop circuitry to lock into system clock information (e.g., program clock reference, or PCR, which may be used to reconstruct the system time clock (STC) at the RP system  110 ) received in an audio, video, or A/V stream (e.g., adaptation field of the transport stream, RTP header, etc.) to facilitate decoding operations and to clock the output of reconstructed audiovisual content. For instance, PTS/DTS values received in a transport stream (or RTP stream header in some embodiments) are compared to the reconstructed STC (generated by the clock circuit  318 ) to enable a determination of when the buffered compressed pictures are provided to the video decoder  310  for decoding (DTS), when the buffered, decoded pictures are output by the video decoder  310  (PTS) to display and output logic  330  for processing and subsequent presentation on a display device  112 , and which PIDs to extract for the appropriate audio (e.g., pitch-preserving audio, etc.). In some embodiments, clock circuit  318  may comprise plural (e.g., independent or dependent) circuits for respective video and audio decoding operations. Although described in the context of hardware circuitry, some embodiments of the clock circuit  318  may be configured as software (e.g., virtual clocks) or a combination of hardware and software. Further, in some embodiments, the clock circuit  318  is programmable. 
     The RP system  110  further comprises, in one embodiment, a storage device  320  (and associated control logic) to temporarily store buffered content and/or to more permanently store recorded content. Memory  322  in the RP system  110  comprises volatile and/or non-volatile memory, and is configured to store executable instructions or code associated with an operating system (O/S)  324 , and one or more applications  326  (e.g., interactive programming guide (IPG), video-on-demand (VoD), WatchTV (associated with broadcast network TV), RTP/RTCP, among other applications such as pay-per-view, music, personal video recording (PVR), driver software, etc.). 
     Further included in one embodiment of memory  322  is pacing logic  114  and buffer management logic  116 , referred to previously, and which in one embodiment is configured in software. In some embodiments, the pacing logic  114  and buffer management logic  116  may be configured in hardware, or a combination of hardware and software. The pacing logic  116 , which operates in conjunction with the decoding logic of the media engine  306  and the demux  304 , is responsible for interpreting auxiliary data that facilitates the decision of which pitch-preserving audio packets to use for substitution and which 1× audio packets to replace with the pitch-preserving audio packets, managing the substitution between pitch-preserving audio and 1× audio when auxiliary data is not present, and directing the pacing-up or pacing-down of the video decoder clocking rate (e.g., via cooperation with the clock circuit  318 ) to enable sped-up or slowed-down video decoding, respectively. 
     In one embodiment, the pacing logic  114 , in cooperation with the decoding logic and demux  304 , remaps the PIDs of the 1× audio to another PID value, and ascribes the PIDs previously identifying the 1× audio to the pitch-preserving audio for use by decoding logic. In some embodiments, auxiliary data sent in the transport stream or a separate stream directs the decoding logic (with or without pacing logic intervention) to decode PID values associated with the pitch-preserving audio in place of the PIDs associated with the 1× audio. In some embodiments, selection of the appropriate audio track (selected from among plural track rates, including real-time audio) is implemented without signaling or PID remapping, where the pitch-preserving audio is selected based on comparing (e.g., by the decoding logic or pacing logic  114  in cooperation with the decoding logic) the adjusted video decoding rate with a matching rate from one of the corresponding audio tracks. 
     The buffer management logic  116  tracks buffer capacity requirements in the context of application resources and application demands, and alone or in cooperation with RTP/RTCP application software in the RP system  110 , effects the generation of requests to upstream network devices for pitch-preserving audio when desired or needed for buffer expansion or contraction, and further coordinates with the pacing logic  114  to facilitate video decoding rate adjustment for pitch-preserving audio processing. Note that functionality of the pacing logic  114  and/or buffer management logic  116  may be combined and/or integrated with one or more other logic of the RP system  110 , such as decoding logic of the media engine, the RTP/RTCP logic, etc. 
     In some embodiments, particularly with sufficient processing resources, the pacing logic  114  in cooperation with the buffer management logic  116  may be configured to generate pitch-preserving audio in buffer expansion or contraction implementations. For instance, for incoming MPEG-2 encapsulated audio, the RP system  110  may extract transport packets from the RTP or the UDP stream, extract audio from the transport packets, decode the audio and process the decoded audio to derive pitch-preserving audio, encode the pitch-preserving audio, and generate a new audio stream to feed to the demux  304 . 
     The RP system  110  is further configured with the display and output logic  330 , as indicated above, which includes graphics and video processing pipelines, among other circuitry, as known in the art to process the decoded pictures and associated audio and provide for presentation (e.g., display) on, or associated with, display device  112 . A communications port  332  (or ports) is further included in the RP system  110  for receiving information from and transmitting information to other devices. For instance, the communication port  332  may feature USB (Universal Serial Bus), Ethernet, IEEE-1394, serial, and/or parallel ports, etc. In addition, communications port  332  may be configured for home networks (e.g., HPNA/MoCA, etc.). The RP system  110  may also include an analog video input port for receiving analog video signals. 
     One having ordinary skill in the art should understand in the context of the present disclosure that the RP system  110  may include other components not shown, including a compression engine, memory, decryptors, samplers, digitizers (e.g., analog-to-digital converters), multiplexers, conditional access processor and/or application software, driver software, Internet browser, among others. Further, though the pacing logic  114  and buffer management logic  116  are illustrated as residing in memory  322 , it should be understood that one or more of pacing logic  114  and buffer management logic  116  may be incorporated in the media engine  306  in some embodiments, or elsewhere, such as in the O/S  324 , among other locations or in conjunction with other logic of the RP system  110 . Similarly, in some embodiments, functionality for one or more of the components illustrated in, or described in association with,  FIG. 3  may be combined with another component into a single integrated component or device. 
     Having described various components of one or more embodiments of an AVP system, attention is directed to the schematic diagram  400  shown in  FIG. 4 , which illustrates one example embodiment of an AVP method in a fast channel change implementation. Shown is a timing diagram, not necessarily to-scale, with a vertical axis  402  corresponding to a stream time-base and a horizontal axis  404  corresponding to a decoder playout time base, the horizontal axis  404  comprising an interval of time  406 . The interval  406  comprises an A/V presentation commencement time of zero (0), and an end of the interval represented beneath the horizontal axis  404  as “A,” as further explained below. Shown during the interval  406  are two lines  408  (dotted) and  410  (interrupted dash). The dotted line  408  corresponds to pitch-preserving audio and video played-out at the same decoding rate (e.g., 0.8×, though other values may be used in some embodiments), which is a rate that is slower than the 1× rate of A/V programming received from an upstream network device, the latter represented by the interrupted dashed line  410 . The dashed line  412  corresponds to the playout of A/V programming at the 1× rate, and commences at the end (“A”) of the interval  406 . Portion  414  corresponds to the initial audio-video time offset that is conventionally known. 
     At a time corresponding to commencement of a channel change (or other stream transition event), a linear A/V stream is received by the RP system  110  at, for instance, a 1× rate, as represented by interrupted dashed line  410 . However, as noted by the portion  414 , there exists, as conventionally known, a time-offset between audio and video of the received A/V stream (e.g., due to differences in buffering time between audio and video, FEC operations, etc.). This offset manifests itself to a viewer in the form of a lack of synchronization between what an actor in the video programming segment says and what his lips would appear to convey (i.e., lip synch issues). In one AVP system embodiment, the 1× A/V stream is not played out initially. Instead, 1× audio is replaced with the 0.8× pitch-preserving audio, and the video decoding rate is slowed (e.g., 0.8×). In other words, the playout initially (e.g., during the interval  406 ) comprises the slowed video and pitch-preserving audio (e.g., the latter received in the multiplex or via a separate stream) in synchronization with each other (e.g., same PTS values, no lip synch discrepancies), as shown by the dotted line  408 . At a time corresponding to the end of the interval  406  (“A”), the pitch-preserving audio is substituted with (replaced by) the 1× audio, and the video decoding rate resumes at 1× for real-time playout, as shown by the dashed line  412 . That is, the original 1× audio catches up (same PTS value) with the original 1× video at this point (“A”), and audio playout switches from the pitch-preserving audio to the original (1×) audio (and the video decoding rate is adjusted). Without the initial playout of the adjusted rate video and pitch-preserving audio, synchronized A/V presentation does not start earlier than point “A.” 
     Attention is now directed to the schematic diagram  500  of  FIG. 5 , which illustrates one example embodiment of an AVP method in a buffer management (e.g., expansion) implementation. Note that similar principles apply for buffer contraction. As indicated above, buffer expansion or contraction may arise based on a given application environment. For instance, buffer expansion (a larger buffer) may be desired or needed in view of the delay inherent in the increased transfer times associated with retransmissions. Another example includes FEC block-re-adjustment. Certain embodiments of an AVP system may expand the buffer without halting presentation of the A/V programming (e.g., on-the-fly buffer expansion), and/or without negatively impacting (or mitigating negative impact) the viewer experience. In some embodiments, the AVP system may allow minor, yet mitigated suspension of playout. Shown is a vertical axis  502  corresponding to segmental reduced rate (e.g., 0.8×, though not limited to this value) time base, and a horizontal axis  504  corresponding to a headend playout time base (e.g., the time frame a viewer lives in). The headend playout time base  504  comprises two successive intervals  506  and  508  of equal length (e.g., 2 seconds per interval, though not limited to this value or equal length intervals). Though shown as two successive intervals, some embodiments may employ buffer expansion or contraction in a greater quantity of intervals, or skip one or more intervals during a defined period of time during which expansion or contraction is implemented. The dashed line  510  corresponds to 1× audio (e.g., real-time audio programming) over the span of at least the two successive intervals  506  and  508 . It is noted that video is omitted from this diagram  500 , though it should be understood that the AVP system reduces the video decoding rate contemporaneously with the pitch-preserving audio processing to effect an incremental video buffer size increase concomitantly with the audio buffer size increase. The dotted lines  512  and  516  correspond to the respective pitch-preserving audio that replaces the real-time audio at the start of each interval  506  and  508 . That is, a pitch-preserving audio timestamp matches a real-time audio timestamp at least once for each applied interval  506  and  508 . The overlap  514  and  518  of the pitch-preserving audio associated with each interval  512  and  516  corresponds to audio that is never played out. For example, in general, when slowing down (pacing-down) audio, practically speaking, it is an attempt to playout, say, 10 seconds of audio over 12 seconds. Using this 10 seconds/12 seconds example, the overlap corresponds to 2 seconds of pitch-preserving audio for a given segment never playing out. The overlaps  514  and  518  reflect this condition. Instead of playing-out the audio corresponding to the overlaps  514  and  518 , audio playout commences with pitch-preserving audio corresponding for the next discrete interval (e.g.,  508 ), timed to coincide with the real-time playout at commencement of the interval based on the RTP or transport level timestamp mechanisms. Also shown are time portions  520  and  522 , which each correspond to, in this example, 1.6 seconds of audio played out over the 2 second interval. Note that, although 2 second intervals are shown for the horizontal axis  504 , other values may be used. 
     With regard to one example method, the schematic diagram  500  reflects or illustrates an opportunity every two seconds to play out the audio at a slower rate. Stated differently, at the commencement of each interval  506  and  508 , the real-time audio and video of the A/V programming match the reduced rate video and pitch-preserving audio, and the paced-down audio is maintained over the respective interval  506  and  508  to enable an incremental expansion of the buffer. A segment of pitch-preserving audio replaces the 1× audio at the start of interval  506  (in synchronization with a reduced rate video), and plays out at the 0.8× playout until the start of the next discrete interval  508 . At commencement of the next interval  508 , a segment of pitch-preserving audio replaces the 1× audio (and hence at this point, the 1× audio matches the 0.8× audio). As explained above, these segments of pitch-preserving audio and real-time audio can be matched at the start of each interval  506  and  508  based on PCR and timestamp information in the transport stream (e.g., adaptation field) or based on RTP timestamping mechanisms. This process of replacement at discrete intervals continues until the buffer management logic  116  determines that sufficient additional buffer space has been generated. Thus, the RP system  110  plays out audio using the pitch-preserving, 0.8× audio over each 2 second interval to dynamically increase the buffer size. In this example, the buffer size is incrementally increased by 400 milliseconds (ms) after each 2 second interval (2.0−1.6). As indicated above, the same applies to video, where video is played out at 0.8× speed over the same intervals. As indicated above, other values for playout rate may be used. 
     It is noted that, the buffer expansion (or contraction) may occur responsive to a stream changing event (e.g., automatically based on pre-configured settings of the RP system  110 ), or based on a feedback request as explained above. 
     With regard to contraction, a similar process is employed, except with an increase in rate (and receipt and processing of increased-rate, pitch-preserving audio samples). 
     It is noted that transitions from the pitch-preserving audio stream to the real-time (e.g., 1×) audio stream may be smoothed (e.g., made seamless) by the application of interpolation filters that are part of the pacing logic  114  or a separate module in the RP system  110 . 
     The codec logic  212 , pitch logic  214 , encryption logic  216 , pacing logic  114 , buffer management logic  116 , and media engine  306  may be implemented in hardware, software, firmware, or a combination thereof. To the extent certain embodiments of the codec logic  212 , pitch logic  214 , encryption logic  216 , pacing logic  114 , buffer management logic  116 , and media engine  306  or a portion thereof are implemented in software or firmware, executable instructions for performing one or more tasks of the codec logic  212 , pitch logic  214 , encryption logic  216 , pacing logic  114 , buffer management logic  116 , and media engine  306  are stored in memory or any other suitable computer readable medium and executed by a suitable instruction execution system. In the context of this document, a computer readable medium is an electronic, magnetic, optical, or other physical device or means that can contain or store a computer program for use by or in connection with a computer related system or method. 
     To the extent certain embodiments of the codec logic  212 , pitch logic  214 , encryption logic  216 , pacing logic  114 , buffer management logic  116 , and media engine  306  or a portion thereof are implemented in hardware, the codec logic  212 , pitch logic  214 , encryption logic  216 , pacing logic  114 , buffer management logic  116 , and media engine  306  may be implemented with any or a combination of the following technologies, which are all well known in the art: a discrete logic circuit(s) having logic gates for implementing logic functions upon data signals, an application specific integrated circuit (ASIC) having appropriate combinational logic gates, programmable hardware such as a programmable gate array(s) (PGA), a field programmable gate array (FPGA), etc. 
     Having described various embodiments of AVP system, it should be appreciated that one method embodiment  600 , shown in  FIG. 6 , and implemented in one embodiment by logic (hardware, software, or a combination thereof) in a downstream network device of an AVP system comprises receiving at the network device a multiplex of compressed versions of a first video stream and a first audio stream, each corresponding to an audiovisual (A/V) program, the first video stream and the first audio stream each received at a first playout rate ( 602 ); receiving a compressed version of a second audio stream, the second audio stream received at a pitch-preserving, second playout rate different than the first playout rate ( 604 ); simultaneously presenting decoded versions of the first video stream and the second audio stream at the second playout rate for a first interval of time ( 606 ); and simultaneously presenting decoded versions of the first video stream and the first audio stream at the first playout rate for a second interval of time, the second interval of time immediately following the first interval of time ( 608 ). 
     Another method embodiment  700 , shown in  FIG. 7 , and implemented in one embodiment by logic (hardware, software, or a combination thereof) of an upstream network device of an AVP system comprises providing by the network device a multiplex of compressed versions of a first video stream and a first audio stream, each corresponding to an audiovisual (A/V) program, the first video stream and the first audio stream each corresponding to a first playout rate and un-synchronized with each other for an initial playout portion ( 702 ); and providing a compressed version of a second audio stream, the second audio stream corresponding to a pitch-preserving, second playout rate different than the first playout rate, the second audio stream synchronized to the initial playout portion of the first video stream when the first video stream is played out at the second playout rate, the first audio stream replaceable by the second audio stream for the initial playout portion ( 704 ). 
     Another method embodiment  800 , shown in  FIG. 8 , and implemented in one embodiment by logic (hardware, software, or a combination thereof) of a downstream network device of an AVP system comprises receiving by the network device a multiplex of a compressed video stream and a compressed audio stream, the multiplex comprising a succession of intervals corresponding to a video program corresponding to a first playout rate ( 802 ); and at the start of each interval, replacing the compressed audio stream with a compressed, pitch-preserving audio stream corresponding to a second playout rate different than the first ( 804 ). 
     Another method embodiment  900 , shown in  FIG. 9 , and implemented in one embodiment by logic (hardware, software, or a combination thereof) of an upstream network device of an AVP system comprises providing by the network device a multiplex of a compressed video stream and a compressed audio stream, the multiplex comprising a succession of intervals corresponding to a video program corresponding to a first playout rate ( 902 ); and providing a compressed, pitch-preserving audio stream for each interval of the succession of intervals, each of the pitch-preserving audio streams corresponding to a second playout rate different than the first, the pitch-preserving audio stream synchronous to the video stream when the video stream is played out at the second playout rate ( 904 ). 
     Any process descriptions or blocks in flow charts or flow diagrams should be understood as representing modules, segments, or portions of code which include one or more executable instructions for implementing specific logical functions or steps in the process, and alternate implementations are included within the scope of the present disclosure in which functions may be executed out of order from that shown or discussed, including substantially concurrently or in reverse order, depending on the functionality involved, as would be understood by those reasonably skilled in the art. In some embodiments, steps of a process identified in  FIGS. 6-9  using separate boxes can be combined. Further, the various steps in the flow diagrams illustrated in conjunction with the present disclosure are not limited to the architectures described above in association with the description for the flow diagram (as implemented in or by a particular module or logic) nor are the steps limited to the example embodiments described in the specification and associated with the figures of the present disclosure. In some embodiments, one or more steps may be added to one or more of the methods described in  FIGS. 6-9 , either in the beginning, end, and/or as intervening steps. 
     It should be emphasized that the above-described embodiments of the present disclosure are merely possible examples of implementations, merely set forth for a clear understanding of the principles of the AVP systems and methods. Many variations and modifications may be made to the above-described embodiment(s) without departing substantially from the spirit and principles of the disclosure. Although all such modifications and variations are intended to be included herein within the scope of this disclosure and protected by the following claims, the following claims are not necessarily limited to the particular embodiments set out in the description.