Abstract:
An apparatus and method is disclosed in which a buffer receives a first content stream carrying a content channel signal. The first content stream carries the content channel signal at a rate substantially greater than the streaming content playout rate, for initially loading the buffer. The buffer switches its reception of the content channel signal from the first content stream to a second content stream. The second content stream is at a rate substantially the same as the streaming content playout rate. Generally, this switch occurs when some predefined threshold of the content channel signal is buffered.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to the downloading of streaming content. 
       BACKGROUND OF THE INVENTION 
       [0002]    Proposed methods for carrying digital video programming from a Head End (HE) to a Set Top Box (STB), over a Digital Subscriber Line (DSL) connection, now exist within the industry. In many cases, the digital video is in the form of compressed digital video such as Moving Pictures Experts Group (MPEG) 2 or MPEG 4. Many of these systems utilize video multicast within the HE equipment for efficient distribution of the video to the edge of the network. An important limitation of these systems is that a DSL link has only enough bandwidth to handle one or two video streams (programs) simultaneously. 
         [0003]    Because of the bandwidth limitation, one problem that these systems experience is jitter. Jitter is a deviation in, or displacement of, the bit arrival times of a digital signal. Some of the principle causes of jitter include, inter alia, queues in network switches and packet collisions requiring subsequent retransmission. Jitter may also be added to the video stream as the result of the asynchronous transfer mode (ATM) switching or Internet Protocol (IP) routing. Furthermore, jitter may occur as a result of adding to a video stream as the video is distributed within the home from the DSL modem to the STB&#39;over, for example, an Ethernet. 
         [0004]    Proposed methods for correcting jitter include, for example, the use of a large de-jittering buffer in the front end of the decoder in the STB. However, de-jittering buffers add a significant and undesirable time delay to the signal. For example, for a de-jittering buffer designed to hold five seconds of video, there would be a five-second delay from the time the video is received by the STB to the time that the video is displayed. 
         [0005]    Buffering creates additional problems. For example, if a user changes channels and the system merely connects the STB to a real time video stream, the user will have to wait five seconds for the buffer to fill before a picture will be displayed. This would spoil the channel changing experience that many people expect. For example, many people like to “surf” channels to examine what is on a several particular television channels before settling on a program. Having a long delay each time a new channel is selected would be at odds with the ability to rapidly surf through the various offered channels, and these viewers would find such a delay particularly vexing. 
       SUMMARY OF THE INVENTION 
       [0006]    Therefore, the present invention is a system and method for providing de-jittered streaming content while providing a substantially instantaneous channel changing experience. In accordance with the principles of the present invention, a buffer receives a first content stream carrying a content channel signal. The first content stream carries the content channel signal at a rate substantially greater than the streaming content playout rate. The buffer switches its reception of the content channel signal from the first content stream to a second content stream. The second content stream is at a rate substantially the same as the streaming content playout rate. Generally, this switch occurs when some predefined threshold of the content channel signal is buffered. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]    The present invention will be described below in more detail, with reference to the accompanying drawings: 
           [0008]      FIG. 1  illustrates a network capable of delivering DSL video in accordance with the principles of the present invention; 
           [0009]      FIG. 2  shows a flow diagram of a channel change mechanism in accordance with the principles of the present invention; and 
           [0010]      FIG. 3  shows a data transfer from a source buffer to a de-jitter buffer during initial viewing in accordance with the principles of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0011]    The present invention delivers video data to a STB at a rate substantially greater than a display rate for an initial period of time after a new channel has been selected. During this initial time period, a STB buffer is loaded to a desired level. Upon loading the STB buffer, the video connection can be switched to a video multicast connection wherein the STB video decoder receives buffered video from the STB buffer at substantially the same rate as the video display rate. Further, although described in terms of video, the concept and principles of the present invention apply to any form of streaming digital, whether it is video, audio, data, or a combination thereof. 
         [0012]    It is to be understood that the present invention may be implemented in various forms of hardware, software, firmware, special purpose processors, or a combination thereof. It is also understood that the present invention may be implemented in software as an application program tangibly embodied on a program storage device. The application program may be uploaded to, and executed by, a machine comprising any suitable architecture. In an exemplary embodiment, the machine is implemented on a computer platform having hardware such as one or more central processing units (CPU), a random access memory (RAM), and input/output (I/O) interface(s). The computer platform also includes an operating system and micro instruction code. The various processes and functions described herein may either be part of the micro instruction code or part of the application program (or a combination thereof) which is executed via the operating system. In addition, various other peripheral devices may be connected to the computer platform such as an additional data storage device and a printing device. 
         [0013]    It is to be further understood that, because some of the constituent system components and method steps depicted in the accompanying description and figures may be implemented in software, the actual connections between the system components (or the process steps) may differ depending upon the manner in which the present invention is programmed. Given the teachings of the present invention provided herein, one of ordinary skill in the related art will be able to contemplate these and similar implementations or configurations of the present invention. 
         [0014]    According to an embodiment of the present invention, in systems in which the quantity and severity of jitter is frequently a problem, such as in distribution across the Internet, larger de-jittering buffers can be provided on the front end of the decoder which would thereby decrease the instances and severity of jitter by increasing the amount of available buffered video. 
         [0015]    Additionally, the present invention can apply to any system distributing video over the Internet from a video Server. The final distribution can be via DSL, dial up, cable modem, Integrated Services Digital Network (ISDN), or any other means of connecting to the Internet. The present invention also applies to systems or network connections that use multicast signals for efficient distribution or simply duplicate the stream and send out individual streams. 
         [0016]    Referring to  FIG. 1 , an illustrative example of a network for delivering DSL video is shown including, inter alia, a video server  101 , and ATM switch  102 , a Service Control. Processor (SCP)  103 . The network includes a DSL Access Multiplexor (DSLAM)  104 , for connecting multiple DSL users to the network. The DSLAM  104  connects to the ATM switch  102 . The DSLAM  104  demultiplexes the signals and forwards them to appropriate individual DSL connections. The network further includes a DSL Terminator  105 , router  106 , customer premise equipment (CPE)  107 , a STB  108 . The video server  101  includes a buffer for each video channel that may be chosen. These buffers can be sized to handle a worst-case jitter scenario that may be displayed at the STB  108 , including jitter contributed by the ATM distribution and jitter caused by distribution within a local area network such as Ethernet. 
         [0017]    Jitter can range from a few milliseconds to several seconds depending on the distribution channel used. A communication channel for channel changing commands exists between the STB  108  and the HE equipment  109 . When a customer turns on a channel or changes channels, a command is sent from the STB  108  to the HE  109 . The SCP  103  sets up a connection between the video server  101  and the STB  108 . The video server  101  provides video from a HE buffer to the STB buffer  108  at a substantially higher speed (e.g., double-speed) than a normal video viewing speed(e.g., thirty frames per second). 
         [0018]    In one exemplary embodiment of the invention, during the transitory period, the connection is set up logically as a point-to-point connection. No other STB will receive the same higher speed stream at exactly the same time. The STB receives the higher speed video stream and starts to display the stream immediately. However, it displays the video at the normal viewing speed. Thus, the video arrives at the STB at a rate faster than it is being displayed or consumed. Accordingly, the de-jittering buffer in the front end of the STB is loaded with video. Once the STB buffer has been filled to a desirable level, the SCP switches the video source to a video stream that can be shared among one or more STBs (e.g., multicast). 
         [0019]    Referring to.  FIG. 2 , for live broadcasts, the HE will maintain a buffer that is at least as large as the buffer used for de-jittering in the STB. For example, for a five second STB de-jittering buffer, the HE buffer would store five seconds or more of video. When the customer changes channels, the HE will supply delayed video from the HE buffer at a rate  201  higher, e.g., sixty frames per second, than the video rate for normal viewing  202 , e.g., thirty frames per second. 
         [0020]    In an exemplary embodiment of the invention, the HE buffer is a circular buffer or queue that maintains a level of information. The HE&#39;s transmitter will be merely pulling the data from a progressively later time in the buffer. The buffer-remains full at all times, and can therefore handle multiple clients simultaneously by pulling data from different times in the buffer. Data is transferred out of the buffer at a 1× rate, even though data is being sent to the STB buffer at a higher rate, e.g., 3×. However, from the perspective of the STB, it appears that the HE buffer empties. 
         [0021]    Since the video is being displayed at the normal speed, but the stream is arriving at the higher speed, the de-jittering buffer in the front end of the decoder will fill to a desirable level. According to the example, once this buffer has filled with five-seconds of video, the HE ceases sending video to the STBs at the higher speed and begins to send video at the normal viewing speed. This can happen in a one-to-one relationship, but can also happen by merely switching the input of the STB to a multicast or broadcast video stream. The Multicast stream is sent in real-time. During the initial stage, the five second delay is due to five seconds of old data being sent from the HE buffer. After switching to multicast, all of the delay is due-to five seconds of video stored in the STB buffer. 
         [0022]    The switch from the HE buffered signal to the video stream can be controlled from the HE, because the HE knows at what point the STB has received all of the delayed video from the HE delay buffer and the only video left to send is the real-time video that is being used to fill the delay buffer. 
         [0023]    Referring, to  FIG. 3 , during the transitory channel changing period  301 - 303 , data is transferred from a HE buffer  304 - 307  to the STB buffer  308 - 311  until the desired delay is established before switching to the buffered broadcast stream  312 . Note that this method can apply to real-time broadcasts such as sports programs, movies, or any other type of video programming. 
         [0024]    It is also possible that some, video data may arrive late during the initial few moments after the second change. But the packet delay associated with most video packets is expected to be less than the maximum delay, so this is not expected to be objectionable. Additionally, the likelihood of encountering a late packet will decrease as the decoding buffer fills. 
         [0025]    Having described embodiments for a system and method of de-jittering a DSL video distribution system connection, it is noted that modifications and variations can be made by persons skilled in the art in light of the above teachings. It is therefore to be understood that changes may be made in the particular embodiments of the invention disclosed which are within the scope and spirit of the invention as defined by the appended claims. Having thus described the invention with the details and particularity required by the patent laws, what is claimed and desired protected by Letters Patent is set forth in the appended claims.