Patent Publication Number: US-10326810-B2

Title: Parallel streaming

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a continuation of U.S. Patent Application titled “Parallel Streaming”, Ser. No. 14/629,348, filed Feb. 23, 2015, which is a continuation of U.S. Patent Application titled “Parallel Streaming”, having Ser. No. 13/777,241, filed Feb. 26, 2013, now patented as U.S. Pat. No. 8,966,014, issued Feb. 24, 2015, which is a continuation of U.S. Patent Application entitled “Parallel Streaming”, Ser. No. 12/722,580, filed Mar. 12, 2010, now patented as U.S. Pat. No. 8,386,621, issued Feb. 26, 2013. The subject matter of these related applications is hereby incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     Embodiments of the present invention relate generally to digital media and, more specifically, to a digital content distribution system for streaming a digital content file, in parallel, using multiple connections to a content distribution network. 
     Description of the Related Art 
     Digital content distribution systems typically include a content server, a content player, and a communications network connecting the content server to the content player. The content player may be configured to playback, e.g., movies, televisions shows, sporting events, music productions, etc, as stored in a digital content file. 
     In practical scenarios, a group of content servers may be configured within a communications network to form a content distribution network (CDN). The content distribution network may also include a directory server configured to provide a list of titles of available from the CDN and associate each title with a reference mechanism, such as a uniform resource locator (URL), used to access the title. When a user interacts with the content player to initiate playback of a specific title, the content player may post a request to the directory server for a reference to content servers hosting the file. Note, the files are often hosted by multiple content servers. The content player then downloads and plays the title from the CDN using the reference provided by content directory server. 
     The process of playing the digital content file includes decoding the data to generate audio and video signals sent to audio speakers and a display screen. Playback typically occurs using a technique known as “streaming,” where the content is transmitted over the network to the content player, which decodes and plays the media file while data is being received. To account for variable latency and bandwidth within the communications network, a content buffer queues some of the audio/video data ahead of the content data actually being played. During moments of network congestion, which leads to lower available bandwidth, less audio/video data is added to the buffer, which drains down as content data is being de-queued during streaming playback. However, during moments of high network bandwidth, the buffer is replenished, adding data to the buffer. In practical systems, the content buffer may queue content data corresponding to a time span ranging from seconds to more than a minute. 
     Streaming media files over the Internet has become increasingly popular as the availability of broadband data communication services has improved. As is known, the playback quality of a program depends significantly on the bit-rate at which the video is encoded. In digital audio and video applications, bit rate refers to the number of data bits used per unit of playback time to represent audio and video. In general, the higher the bit-rate the higher the visual and auditory quality of a program and the longer it takes to download a portion of the program over a data network at a fixed bandwidth or transmission rate. The better the throughput that can be achieved using the network bandwidth available to a content player, the higher a bit-rate encodings that may be used for playback. Further, the better the throughput of a connection, the less likely it is that a buffer under-run will occur (i.e., the less likely that streaming playback will be interrupted). 
     SUMMARY OF THE INVENTION 
     One embodiment of the present invention includes a method for downloading, in parallel, a digital content file using a plurality of network connections. This method may generally include receiving a list of one or more content servers hosting a copy of the digital content file, establishing the plurality of network connections with the one or more content servers, and receiving metadata describing a plurality of sequential portions of the digital content file. Each time one of the network connections is determined to be idle, one of the portions of the digital content file may be selected to be downloaded over the idle network connection and the selected portion is downloaded from the content server using the idle network connection. This method may also include storing each downloaded portion of the digital content in a content buffer and playing back the portions of content downloaded and stored in the content buffer. 
     In a particular embodiment, the step of selecting one of the portions of the digital content file to be downloaded over the idle network connection may itself include predicting a first time required to download a next sequential portion of the digital content file and predicting at least a second time required for each active network connection to complete downloading one of the portions of the digital content file and to complete downloading the next sequential portion. This method may further include tentatively assigning the next sequential portion to be downloaded using the network connection with the lowest predicted time. In response to determining the tentative assignment has been made to the idle network connection, the tentative assignment may be confirmed. Otherwise, in response to determining the tentative assignment has not been made to the idle network connection, the predicting steps may be repeated using a second next sequential chunk until a portion of the digital content file is assigned to the idle network connection. 
     Still another embodiment of the invention provides a method for downloading, in parallel, a digital content file using a plurality of network connections. This method may generally include receiving a list of one or more content servers hosting a copy of the digital content file, and launching, for each of the plurality of network connections, a buffering thread. Each buffering thread may be configured to establish one of the network connections, download portions of the digital content file assigned by the scheduling thread, and store the downloaded portions in a content buffer. This method may further include launching a scheduling thread configured to select which network connection to use in downloading each of a plurality of portions of the digital content file and launching a playback thread configured to play the digital content stored in the content buffer. 
     Other embodiments include, without limitation, a computer-readable medium that includes instructions that enable a processing unit to implement one or more aspects of the disclosed methods as well as a system configured to implement one or more aspects of the disclosed methods. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       So that the manner in which the above recited features of the present invention can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments. 
         FIG. 1  illustrates a content distribution system configured to implement one or more aspects of the present invention. 
         FIG. 2  is a more detailed view of the content player of  FIG. 1 , according to one embodiment of the invention. 
         FIG. 3  illustrates a method for downloading a digital content file from a content distribution network, according to one embodiment of the invention. 
         FIG. 4  illustrates a method for a content player to select a content server from which to request a chunk of audio/video data, according to one embodiment of the invention. 
         FIG. 5A-5C  illustrates an example of a content player streaming a digital content file, in parallel, using multiple network connections, according to one embodiment of the invention. 
         FIG. 6  illustrates a method for updating bandwidth connection data for a given connection between a content player and a content distribution network, according to one embodiment of the invention. 
         FIG. 7  illustrates an example of a content player updating bandwidth connection data for a given connection between a content player and a content distribution network, according to one embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments of the invention provide a technique for downloading a digital content file, in parallel, using multiple network connections established with a content distribution network (CDN). By creating multiple network connections, a better throughput is obtained for streaming a media file to the content player. To stream the media file, the content player downloads a file header associated with a given title, establishes a network connection with multiple content servers (or multiple network connections with a single content server or both) and begins requesting portions of the digital file (referred to as “chunks”). In response, the content servers transmit the requested portions to the content player. As described in greater detail below, the content player may employ a predictive multi-connection scheduling approach to determine which network connection to use in downloading a given chunk. Once received, the chunks may be stored in a buffer prior to being decoded and played back. 
     The predictive multi-connection scheduling approach maximizes the throughput of data for streaming the media file to the client, which may allow higher bit-rate encodings to be streamed, as well as reduce the occurrence of buffer under-runs, thereby improving the overall user experience. 
     In the following description, numerous specific details are set forth to provide a more thorough understanding of the present invention. However, it will be apparent to one of skill in the art that the present invention may be practiced without one or more of these specific details. In other instances, well-known features have not been described in order to avoid obscuring the present invention. 
       FIG. 1  illustrates a content distribution system  100  configured to implement one or more aspects of the present invention. As shown, the content distribution system  100  includes, without limitation, a content player  110  configured to select a digital content file for playback from one of a plurality of content distribution networks  140 . A content directory server  120  is configured to provide the content player  110  with a list of content distribution networks hosting the digital content file. A communications network  150 , such as the internet communications network, provides the communication infrastructure for communication between the content player  110 , content directory server  120 , and the content distribution networks  140 . 
     The content player  110  may be a computer system, a set top box, a mobile device such as a mobile phone, or other computing platform that has network connectivity and is coupled to or includes a display device. Each content distribution network (CDN)  140  comprises at least one computer system configured to service download requests for digital content files from the content player  110 . The digital content file may include any type of encoded (or un-encoded) digital content (data), including, without limitation, movie content, television program content, or audio content. The digital content files may reside on a mass storage system accessible to the computer system, including, without limitation, direct attached storage, network attached file storage, or network attached block-level storage. The digital content files may be formatted and stored on the mass storage system using any technically feasible technique. Any data transfer protocol, such as hypertext transfer protocol (HTTP), may be used to download digital content files from the CDN  140  to the content player  110 . 
     In a practical setting, a plurality of content players  110  connect to a plurality of CDNs  140 . A content directory server  120  may be used to direct a given content player  110  to a specific CDN  140  from which to download a requested digital content file. The content directory server  120  may reside at a network address known to the plurality of content players  110 . The network address may comprise a specific internet protocol (IP) address or a specific universal resource locator (URL), or any other technically feasible network address. 
     The communications network  150  may include a plurality of network communications systems, such as routers and switches, which enable data communication between the content player  110  and the plurality of content distribution networks  140 . Persons skilled in the art will recognize that many technically feasible techniques exist for building the communications system  150 , including the widely used TCP/IP protocols (and higher-layer application protocols) used by the internet. 
     In one embodiment, the content player  110  may transmit a title lookup request  112  to the content directory server  120 . The title lookup request  112  may refer to the title of a particular digital content file, such as “Gone with the Wind.” In response to the title lookup request  112 , the content directory server  120  generates and transmits a CDN list  122  to the content player  110 . The CDN list  122  specifies one or more CDNs  140  that each host a copy of the digital content file named in the title lookup request  112 . For a given title, each CDN list  122  may be different for each content player  110 , and a given content player  110  may receive a different CDN list  122  for each different requested title. 
     In one embodiment, each CDN  140  within the CDN list  122  includes a list of URLs of individual content servers within the CDN  140 . Upon receiving the CDN list  122 , the content player  110  selects at least one CDN  140  from which to download the digital content file named in the title lookup request  112 . For example, the content player  110  may establish multiple connections with a single content server, but may also establish network connections with different content servers in one CDN  140 , or content servers within multiple CDNs  140 . Once the content server (or servers) is selected, the content player  110  proceeds to download chunks of the requested file, and play the digital content file named in the title lookup request  112 . 
     Although the above description shows the content distribution system  100  with one content player  110  and three CDNs  140 , persons skilled in the art will recognize that the architecture of  FIG. 1  contemplates only an exemplary embodiment of the invention. Other embodiments may include any number of content players  110  and/or CDNs  140 . Thus,  FIG. 1  is in no way intended to limit the scope of the present invention. 
       FIG. 2  is a more detailed view of the content player  110  of  FIG. 1 , according to one embodiment of the invention. As shown, the content player  110  includes, without limitation, a central processing unit (CPU)  210 , a graphics subsystem  212 , an input/output (I/O) device interface  214 , a network interface  218 , an interconnect  220 , and a memory subsystem  230 . The content player  110  may also include a mass storage unit  216 . The central processing unit (CPU)  210  is configured to retrieve and execute programming instructions stored in a memory subsystem  230 . The CPU  210  retrieves the programming instructions from the memory subsystem  230  via an interconnect  220 . The CPU  210  is configured to store and retrieve data in the memory subsystem  230  via the interconnect  220 . 
     The graphics subsystem  212  is configured to generate frames of video data, such as a sequence of graphics images, and transmit the frames of video data to display device  250 . The graphics subsystem  212  is coupled to the CPU  210  via the interconnect  220 . In one embodiment, the graphics subsystem  212  is integrated into an integrated circuit, along with the CPU  210 . The display device  250  may comprise any technically feasible means for generating an image for display. For example, the display device  250  may be fabricated using liquid crystal display (LCD) technology, cathode-ray technology, and light-emitting diode (LED) display technology (either organic or inorganic) to produce a visual representation of the frames of video data. An input/output (I/O) device interface  214  is configured to receive input data from user I/O devices  252  and transmit the input data to the CPU  210  via the interconnect  220 . For example, user I/O devices  252  may comprise one or more buttons, a keyboard, and a mouse or other pointing device. The I/O device interface  214  also includes an audio output unit configured to generate an electrical audio output signal. User I/O devices  252  includes a speaker configured to generate an acoustic output in response to the electrical audio output signal. In alternative embodiments, the display device  250  may include the speaker. A television is an example of a device known in the art that can display video frames and generate an acoustic output. A mass storage unit  216 , such as a hard disk drive or flash memory storage drive, is configured to store non-volatile data. The mass storage unit  216  is coupled to the CPU  210  via the interconnect  220 . A network interface  218  is configured to transmit and receive packets of data via the communications network  150 . In one embodiment, the network interface  218  is configured to communication using the well-known Ethernet standard. The network interface  218  is coupled to the CPU  210  via the interconnect  220 . 
     The memory subsystem  230  includes programming instructions and data that comprise an operating system  232 . The operating system  232  performs system management functions such as managing hardware devices including the network interface  218 , mass storage unit  216 , I/O device interface  214 , and graphics subsystem  212 . The operating system  232  also provides process and memory management models for a user interface  234  and a playback application  236 . The user interface  234  provides a specific structure, such as a window and object metaphor, for user interaction with content player  110 . Persons skilled in the art will recognize the various operating systems and user interfaces that are well-known in the art and suitable for incorporation into the content player  110 . 
     The playback application  236  is configured to retrieve a digital content file from a CDN  140  via the network interface  218  and play the digital content file via the graphics subsystem  212  and display device  250 . The playback application  236  requests a CDN list  240 , such as CDN list  122  of  FIG. 1 , from the content directory server  120 . The playback application  236  selects a CDN from the CDN list  240 , as described in greater detail below in  FIG. 3B . The playback application  236  then proceeds to download and buffer the digital content file from a selected CDN  140 . The playback application  236  generates a viewable rendering of the digital content file to a user during a playback process, as described in greater detail below in  FIGS. 3-7 . 
     An audio buffer  242  may be used to store audio data from a piece of digital content downloaded from the selected CDN  140 . In one embodiment, an audio decoder  244  is used to decode data stored in the audio buffer  242  into one or more audio tracks. A video buffer  246  is used to store video data from a piece of digital content downloaded from the selected CDN  140 . A video decoder  248  is used to decode and render data stored in the video buffer  246  into one or more sequences of viewable video frames. The content buffer  245  may provide a unified buffer structure, including the audio buffer  242  and video buffer  246 . In such a case, the audio data and video data are structured into a single stream. Alternatively, the content buffer  245  may configure the audio buffer  242  and video buffer  246  as separate buffers that may be accessed independently for adding or removing data. 
     As noted above, the playback application  236  may be configured to establish a network connection with multiple content servers (or multiple connections with a single content server) and download different chunks of a digital content file in parallel. In one embodiment, the playback application  236  is configured to collect and update connection statistics  241  regarding the prevailing bandwidth conditions experienced between the content player  110  and each such network connection. The connection statistics  241  may be updated periodically at regular intervals or upon the occurrence specified events (e.g., a chunk completes downloading over a given connection). In one embodiment, the scheduling statistics  241  may be used to decide whether to continue to use a given network connection. For example, if the network connection between the content player and one of the content servers falls below a specified threshold (or is performing poorly relative to other connections during a given session) then that connection may be killed. In such a case, a replacement connection may be selected from the CDN list  240  or the digital content file may continue to be streamed using the remaining connections. Further, as described in greater detail below, the connection statistics  241  may be evaluated by the playback application  236  as part of selecting what connection to use to download a given chunk of a digital content file being streamed to the content player  110 . 
       FIG. 3  illustrates a method  300  for streaming a digital content file from a content distribution network  140 , according to one embodiment of the invention. Although the method steps are described in conjunction with the systems of  FIGS. 1 and 2 , persons skilled in the art will understand that any system configured to perform the method steps, in any order, is within the scope of the invention. 
     As shown, the method  300  begins at step  305 , where the playback application  236  receives a user request to play a selected digital content title. For example, the user may enter a selection using one or more of the user I/O devices  252  of  FIG. 2 , such as a keyboard or mouse, remote control, or panel controls integrated with content player  110 . At step  310 , the playback application  236  requests a CDN list  122  for the selected digital content file from the content directory server  120  via a title lookup request  112 . In one embodiment, the content directory server  120  may be accessed over in a communications network using, e.g., a URL known to the content player  110 . As noted above, the CDN list  122  may provide a list of URLs, each corresponding to a content server from which the requested title is available. 
     In addition to the request for the CDN list  122 , the playback application  236  may request metadata describing a layout of the requested digital content file. The metadata may provide a list of portions of the file (i.e., a list of chunks) and provide a layout of the file indicating the position of each chunk, e.g., as a byte offset into the file. Each chunk may represent a distinct segment of audio/video data of the media file. For example, in one embodiment, each digital content file may be encoded using the known MPEG-2 encoding standard. In such a case, each chunk of the encoded digital content file may include a sequence of GOPs corresponding to, e.g., two to three seconds of encoded video data, referenced relative to the byte position of a given GOP in the file. As is known, a “GOP” refers to a group of successive pictures within a coded video stream from which the visible frames are generated, and a GOP is usually about 15 frames long in an NTSC system. Of course, MPEG-2 provides just one example of an encoding standard and others may be used. 
     Additionally, the digital content file may be encoded using a variety of different bit-rates, resulting in a different file size (and byte offset position) for the chunks in each encoding at a distinct bit-rate. In one embodiment, the playback application  236  may select what bit-rate to request based on prevailing bandwidth conditions and the bit rates supported by the content player  110 . Further, the playback application  236  may be configured to switch from one bit-rate encoding to another, based on changes in the prevailing bandwidth conditions. In such a case, the playback application  236  may request the metadata specifying a index of chunks and byte offsets for each available bit-rate encoding. 
     In one embodiment, the metadata describing the chunks of a given digital content file may be stored as a file retrieved from the content directory server. Alternatively, the metadata may be included as a header in each copy of the digital content file. However, as the byte offset positions are the same in each copy of the file (for encodings at the same bit-rate), the content player  110  may be configured to retrieve only one copy of the header (or one copy for each available bit-rate encoding) rather than obtain a duplicate from multiple copies. 
     Once retrieved, at step  315 , the playback application  236  may select one or more CDNs to use to stream the digital content file. While any number of connections may be used, the use of three connections has proven to be effective. Using this as an example, the playback application  236  may establish three distinct network connections with the same content server, establish three connections with different servers in the same CDN, or establish three connections using content servers in distinct CDNs (or combinations thereof). The particular approach used for selecting both how many connections to establish, and which content servers and/or CDNs to use may be tailored suit the needs of a particular case. However, the selection may be based on factors such as, without limitation, customer identity, content title, internet service provider identity, geographic location of the content player  110 , customer history, or prevailing server load or network latency, or any combination thereof. 
     At step  320 , the playback application  236  may launch a scheduling thread. The scheduling thread may provide a unit of execution within the playback application  236  configured to manage the connections between the content player  110  and the content servers selected at step  315 . The scheduling thread may also gather bandwidth statistics used to help determine which connection to use to download any given chunk. In one embodiment, a buffering thread may be created for each connection. Each buffering thread may be configured to download chunks (as assigned by the scheduling thread) and store the resulting audio video data in the content buffer  245 . The scheduling thread may use a simple round-robin approach where, so long as the audio/video data stored in the content buffer  245  is below a threshold, an idle buffering thread is assigned the next sequential chunk of the digital content file to download from the content server. However, in one embodiment, a predictive multi-connection scheduling approach (described relative to  FIGS. 4 and 5A-5C ) is used to increase the throughput obtained from using the multiple network connections to stream the digital content file. 
     At step  325 , the playback application  236  may launch the buffering threads. In turn, each buffering thread may establish a network connection with one of the content servers and begin downloading a chunk of the digital content file assigned by the scheduling thread. For example, in one embodiment, the chunks themselves may be requested using HTTP range requests—by specifying the range of bytes from the digital content file corresponding to a given chunk in the header of an HTTP request message. Of course, other approaches may be used. As the chunks are downloaded, the data may be stored in the content buffer  245 . 
     At step  330 , the playback application  236  may launch a playback thread after a specified amount of data has accumulated in the content buffer  245 . The precise amount of buffered data may be tailored to suit the needs of an individual case, e.g., based on the prevailing bandwidth conditions and the average encoded bit-rate of the digital content file. Once playback begins, the playback application  236  may continue to download chunks of the digital content file from the multiple network connections, store the downloaded chunks in the content buffer, and decode and playback audio/video data until the complete file has been streamed to the content player  110 . 
       FIG. 4  illustrates a method  400  for a content player  110  to select a content server from which to request a chunk of audio/video data, according to one embodiment of the invention. In a particular embodiment, the scheduling thread of the playback application  236  discussed above may perform the method  400  to determine which of multiple network connections to use to download a particular chunk of a digital content file. Of course, persons skilled in the art will understand that any system configured to perform the method steps, in any order, is within the scope of the invention. 
     As shown, the method  400  begins at step  405 , where the scheduling thread determines whether the content buffer  245  is full. Note, the content buffer  245  may not have, strictly speaking, a maximum capacity. Instead, a target amount of data for the buffer may be specified after which additional chunks of the digital content file are not downloaded until the amount of data in the content buffer  245  falls below the target value. In such a case, when the amount of data in the content buffer  245  reaches the target value, active buffering threads continue to download data stored in the content buffer  245 , but additional chunks do not begin downloading. 
     If the content buffer  245  is not full, then at step  410 , the scheduling thread determines whether there is an idle buffering thread (i.e., a thread not actively downloading a chunk of the digital content file). If all the buffering threads are downloading a chunk, then the scheduling tread may simply wait until one becomes available. Of course, initially, the content buffer  245  is empty and none of the buffering threads are active. Accordingly, the scheduling thread may initially assign the first sequential N chunks of the digital content file to N buffering threads, one per connection. 
     As these chunks download, the scheduling thread may monitor the bandwidth experienced by each buffering thread and use this information to select which chunk a given buffering thread should download when it becomes available as well as whether to continue using a given connection. 
     At step  415 , once a buffering thread becomes available (i.e., once a chunk completes downloading over one of the network connections), the scheduling thread identifies the next sequential chunk in the digital content file to download. An example of steps  410  and  415  are illustrated in  FIG. 5A . In particular,  FIG. 5A  illustrates an example timing diagram  500  for a digital content file being streamed to a content player, according to one embodiment of the invention. As shown, a digital content file is being downloaded from three CDNs, CDNa  505 , CDNb  510 , and CDNc  515 . CDNa  505  is downloading chunk  1   525  and CDNb  510  is downloading chunk  2   530 . The partially downloaded content of chunk  1   525  and chunk  2   530  and the fully downloaded content of chunk  3   535  is stored in the content buffer  245 . 
     As further shown, CDNc,  515  completes downloading chunk  3   535  at time t 1    520 . Thus, at time t 1    520 , the buffering thread with the connection to CDNc  535  becomes idle (step  410 ). In response, the scheduling thread determines that the fourth chunk is the next sequential chunk to download (step  415 ). Additionally, the scheduling thread has determined that CDNa  505  and CDNb  510  are experiencing an average download speed of 500 kbps, while CDNc  515  is experiencing a slower speed of only 200 kbps. 
     Returning to the method  400  shown in  FIG. 4 , at step  420 , the scheduling thread predicts the time required for the idle buffering thread to download the next chunk of the digital content file. The prediction may be based on the most recent evaluation of the bandwidth experienced using the network connection between the idle buffering thread and corresponding content server and the byte size of the next chunk of the digital content file. 
     Similarly, at step  425 , the scheduling thread predicts the time required for each active buffering thread to complete downloading a current chunk and to complete downloading the next sequential chunk. Like the prediction made for the idle buffering thread (step  420 ), the prediction for the active buffering threads may be based on the bandwidth statistics collected for each active buffering thread as well as the byte size that remains for the current chunks and the byte size of the next chunk of the digital content file. 
     Steps  420  and  425  are further illustrated in  FIG. 5B . In particular,  FIG. 5B  shows the timing diagram  500 , along with the predictions  540  for how long it will take each of CDNa  505 , CDNb  510 , and CDNc  515  to complete downloading the fourth chunk of the digital content file. In this example, the predictions  540  indicate that CDNb  510  would be able complete downloading chunk  2   530  and downloading the fourth chunk at time t 2    545 , more quickly than the fourth chunk would complete downloading using the network connection to either CDNa  505  or CDNc  515 . 
     At step  430 , the scheduling thread tentatively assigns the next sequential chunk to be downloaded using the network connection with the lowest predicted time. In the example of  FIGS. 5A-5B , the scheduling thread tentatively assigns the fourth chunk of the digital content file to be downloaded over the network connection to CDNb  510 . The assignment remains tentative as the method  400  is used to determine what chunk can be downloaded most efficiently using the idle thread. Accordingly, at step  435 , the scheduling thread determines whether the tentative assignment provides a chunk for the idle buffering thread to download. In the example  FIG. 5B , the fourth chunk is predicted to be more efficiently downloaded using the active buffering thread downloading chunk  2   530  over the network connection to CDNb  510 . Thus, the method  400  returns to step  415 , where the scheduling thread again identifies the next sequential chunk needed to be downloaded. 
     As the scheduling thread has tentatively assigned the fourth chunk to be downloaded using the connection to CDNb  510 , the fifth chunk is identified as the next sequential chunk. Next, the scheduling thread again predicts how long for it would take for the idle buffering thread and for each the active buffering thread to download the fifth chunk (steps  420  and  425 ).  FIG. 5C  illustrates this result, where a tentative assignment of chunk  4   555  is made to CDNb  510 , and a prediction  560  is made representing how long it will take each of CDNa  505 , CDNb  510 , and CDNc  515  to complete downloading the fifth chunk of the digital content file. In this example, the predictions  560  indicate that CDNc  515  would be able complete downloading the fifth chunk at time t 3    550 , more quickly than using either of CDNa  505  or CDNb  510 . Accordingly, the scheduling thread tentatively assigns chunk  5  to the buffering thread connected to CDNc  515  (step  430 ) and determines that a chunk has now been assigned to the idle buffering thread (step  435 ). 
     At step  440 , the scheduling thread confirms the tentative assignment made to the idle buffering thread and discards any other tentative assignments made during the evaluation. In the example of  FIG. 5C , the assignment of the fifth chunk to CDNc  515  is confirmed and the buffering thread associated with this begins downloading the fifth chunk and storing data in the content buffer  245 . At the same time, the tentative assignment of chunk  4   555  to CDNb  510  is discarded. Note, a scenario could develop where a sequence of idle threads are each assigned a chunk out of sequence, leaving a gap in the chunks downloaded to the content player. Accordingly, in one embodiment, the scheduling thread may first determine whether assigning an idle thread to download a chunk out of sequence could lead to a buffer under-run, and if so, assign the next sequential chunk to an idle thread without regard for the predictions made at steps  420  and  425 . 
       FIG. 6  illustrates a method  600  for updating bandwidth connection statistics for a given connection between a content player and a content distribution network, according to one embodiment of the invention. As shown, the method  600  begins at step  605 , where the content player  236  selects to update the connection statistics  241  for one of the network connections being used to download a digital content file. As noted above, the connection statistics  241  may be updated periodically at regular intervals while a file is being streamed or upon the occurrence specified events. For example, the connection statistics  241  may determine the average bandwidth experienced by a given connection while downloading a given chunk, taking into account any chunks being downloaded concurrently by other connections. In one embodiment, the connection statistics  241  may simply reflect the most recent measure of the bandwidth experienced by a given connection while downloading the most recent chunk. Alternatively, the connection statistics  241  for a given connection may reflect a weighted average blending the most recent measure of the bandwidth with previous measurements. 
     At step  610 , the content player  236  may determine how long it took to download the most recent chunk over the selected connection along with the number bytes of data present in the most recent chunk. Additionally, the content player  236  may identify whether any concurrent connection were being used to download other chunks of the digital content file. 
     At step  615 , a measure of bandwidth is determined for the selected connection, adjusted to account for any concurrent network connections used while the most recent chunk was downloaded by the selected network connection. The measure of bandwidth needs to take into account the concurrent connections (if any) as the multiple network connections share the same data communications channel (e.g., a user&#39;s DSL or cable broadband internet connection). That is, the bandwidth experienced by one network connection is impacted by other connections use of the same communication channel. Once determined, the connection statistics for a given connection are updated. 
     For example,  FIG. 7  illustrates a timing diagram  700  for a digital content file being streamed to a content player. Assume for this example, that the content player has been downloading a digital content file from three distinct content servers: one using a network connection with CDNa  705 , another using a network connection with CDNb  710 , and a third using a network connection with CDNc  715 . 
     As shown, the connection with CDNa  705  required a time period of t 1  to download the bytes in a first chunk  720  and the connection with CDNb  710  required a time period of t 2  to download the bytes in second chunk  725 . Illustratively, the first and second chunks  720  and  725  were downloaded without any concurrent connections. Thus, the expected bandwidth available from CDNa  705  may be computed as the ratio of the number of bytes in chunk  1   720  to the time value t 1 . Similarly, a first measure of the expected bandwidth available from CDNb  710  may be computed as the ratio of the number of bytes in the second chunk  725  to the time value t 2 . Or more simply the ratio of bytes to unit time (e.g., seconds). 
     However, a download of a third chunk  730  (using the connection with CDNb  710 ) and a download of a fourth chunk  735  (using the connection with CDNc  715 ) overlap with one another. In one embodiment, the expected bandwidth available from a connection used concurrently with others may be computed as a ratio of the total number of bytes in a chunk to the sum of a time period with no concurrent chunks being downloaded (if any) and a second time period multiplied by the number of concurrent connections. Thus, for the third chunk  730  in the timing diagram  700 , the expected bandwidth available from CDNc  715  may be computed as follows: 
               b   1         t   3     +     2   ⁢     t   4               
where b 1  is the number of bytes in the third chunk  730  and t 3  and t 4  are the time periods labeled in timing diagram  700 . Similarly, a second measure of the bandwidth for CDNb  710  may be computed as:
 
               b   2         2   ⁢     t   4       +     t   5             
where b 2  is the number of bytes in the fourth chunk  735  and t 4  and t 5  are the time periods labeled in timing diagram  700 . Of course, if a third (or more) concurrent connections are present for a period of overlap, additional terms may be added to these equations as appropriate.
 
     One embodiment of the invention may be implemented as a program product stored on at least one computer-readable storage medium residing within the content player  110 . In such an embodiment, the content player  110  comprises an embedded computer platform such as a set top box, and the stored program product enables the methods of  FIGS. 3, 4, and 6  to be performed by the content player  110 . In an alternative embodiment, a program product may be downloaded to a memory within a computer device. For example, the downloaded program product may be executable instructions embedded within an internet web site. In such an embodiment, the content player  110  comprises the computer device, and the downloaded program product enables the methods of  FIGS. 3, 4, and 6  to be performed by the content player  110 . 
     In sum, a technique for playing digital content file on a content player  110  is disclosed using multiple network connections to download portions of a media file, in parallel. By creating multiple network connections, a better throughput is obtained for streaming the media file to the content player. To stream the media file, the content player downloads a file header associated with a given title, establishes a network connection with multiple content servers (or multiple network connections with a single content server or both) and begins requesting portions of the digital file. In response, the content servers transmit the requested portions to the content player. As described above, the content player may employ a predictive multi-connection scheduling approach to determine which network connection to use in downloading a given chunk. Once received, the chunks may be stored in a buffer prior to being decoded and played back. 
     Advantageously, the predictive multi-connection scheduling approach maximizes the throughput of data for streaming the media file to the client, which may allow higher bit-rate encodings to be streamed, as well as reduce the occurrence of buffer under-runs, thereby improving the overall user experience. 
     While the forgoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof. For example, aspects of the present invention may be implemented in hardware or software or in a combination of hardware and software. One embodiment of the invention may be implemented as a program product for use with a computer system. The program(s) of the program product define functions of the embodiments (including the methods described herein) and can be contained on a variety of computer-readable storage media. Illustrative computer-readable storage media include, but are not limited to: (i) non-writable storage media (e.g., read-only memory devices within a computer such as CD-ROM disks readable by a CD-ROM drive, flash memory, ROM chips or any type of solid-state non-volatile semiconductor memory) on which information is permanently stored; and (ii) writable storage media (e.g., floppy disks within a diskette drive or hard-disk drive or any type of solid-state random-access semiconductor memory) on which alterable information is stored. Such computer-readable storage media, when carrying computer-readable instructions that direct the functions of the present invention, are embodiments of the present invention. 
     In view of the foregoing, the scope of the present invention is determined by the claims that follow.