Real-time data rate matching across a medium

Details Real-time data rate matching across a medium Real-time data rate matching across a medium

1998-01-27

2001-06-12

Follansbee, John A. (Department: 2181)

Electrical computers and digital data processing systems: input/

Input/output data processing

Input/output data buffering

C710S029000, C710S057000, C709S233000

Reexamination Certificate

active

06247072

ABSTRACT:

CROSS REFERENCE TO RELATED APPLICATIONS
Not applicable.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
Not Applicable.
BACKGROUND OF THE INVENTION
The present invention relates to receivers of real-time data, such as receivers designed to receive high-quality video and/or audio data streams as one of multiple receiving computers on a network such as a local area network (LAN), a wide area network (WAN), a large corporate internetwork, or the Internet.
Video broadcasting is a way to distribute live or prerecorded video programming to large numbers of users over a digital network without creating network bottlenecks. Video broadcasting lets an organization set up corporate TV network accessible to an essentially unlimited number of users at their personal computers over enterprise LANs and WANs. In video broadcasting, a single video stream (including audio) is distributed using a technique known as IP Multicast, an IETF (Internet Engineering Task Force) standard. Any user wishing to join a multicast session can tap into it from a desktop personal computer at any time during the broadcast, and can leave the session at any time. This technique is highly efficient because it does not consume more bandwidth as the number of users increases.
A number of specifications have been published related to video broadcasting, and a number of broadcasting applications have been made available. These include the following Internet RFCs: RFC-1112, “Host Extensions for IP Multicasting”, August 1989; and RFC-1889 “RTP: A Transport Protocol for Real-Time Applications”, January 1996. Available applications include VAT, an audio conferencing application, and VIC, a video conferencing application, for which source code is available from the Network Research Group of Lawrence Berkeley National Laboratory
(http://www-nrg.ee.lbl.gov/vat/ and
http://www-nrg.ee.lbl.gov/vic/).
In video broadcasting, generally both video and audio are sent from a server to the client or clients over a transmission medium. The video and audio data are generally in a compressed form, and so must be decompressed on the client side. On the server side, the source of data may have video and audio interleaved together, either in a data file or from a live encoder.
The data can be transmitted either with or without splitting the audio data on the server. If the data are split on the server, each stream is transmitted independently to unique ports on the transmission medium. (A port is a logical channel in a communications system. The Internet TCP and UDP transport layer protocols use port numbers to demultiplex messages.) Otherwise, the data is split on the client, in either case generating packets of encoded audio and video data.
Audio and video compression create an encoded bitstream that is segmented into packets of encoded data. A transmission medium will generally also transmit data in packets, and typically one or more packets of compression encoded data can fit into a transmission medium packet.
The transmitted video data is synchronized to the audio data. Synchronization between video and audio is generally established by the use of time stamps, which are attached to each encoded data packet.
SUMMARY OF THE INVENTION
The methods and apparatus of the invention provide rate matching for real-time data across a transmission medium.
In general, in one aspect, the invention features apparatus and methods for matching data rates useful for a receiver receiving real-time data over a medium. Implementations of the invention feature a process establishing a buffer in a receiver; receiving source data from a source having a nominal source data rate, the received source data arriving at an incoming data rate that differs from time-to-time from the nominal source data rate; filling the buffer with source data as it is received at the incoming data rate and emptying the buffer to provide data for consumption in real time at a consumption data rate; setting a rate-matching factor M, the factor M affecting the rate at which the buffer is emptied; and tracking the level of data in the buffer and resetting the value of M to increase the rate at which the buffer is emptied when the buffer fills above a target range, and resetting the value of M to decrease the rate at which the buffer is emptied when the buffer empties below a target range.
Advantageous implementations of the invention may include one or more of the following features. The target range is reset when the buffer fills either above the target range or empties below the target range. The factor M is reset when the buffer fills either above the target range or empties below the target range. The factor M is reset when the buffer hits a target level within the target range. The consumption data rate is fixed and nominally equal to the source data rate. The source data is an IP Multicast video broadcast including video and audio data. The source data is MPEG compressed. The received source data is decompressed before application of the factor M. The received source data is decompressed after application of the factor M. When M is greater than one, the received data is consumed more quickly by deleting data from the received data; and when M is less than one, the received data is consumed more slowly by adding data to the received data. The incoming data rate and the consumption data rate experience jitter with respect to each other over time. The received source data includes audio and video data, and data is added to or deleted from the received audio data to create modified audio data and synchronizing the received video data to the modified audio data. The source data is received from a source that cannot be caused to change its rate of transmission by the receiver.
Among the advantages of the invention are one or more of the following. Operation of the invention is robust in the presence of substantial jitter and noise. Operation of the invention is robust when receiving data from a source whose data rate deviates over time from its nominal rate. Operation of the invention avoids uncontrolled drift in the amount of buffered data in the receiver. The amount of buffered data in a receiver can be controlled.
Other features and advantages of the invention will become apparent from the following description and from the claims.


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Precept Software Inc.—Press Release, “Precept Unveils First General-Purpose Standards-Based Software Platform For Running Multimedia On Existing Networks,” Cupertino, California, Jan. 22, 1996, 1 page, downloaded from WWW.
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MBONE Press Release, “30-Day Free Trial of Precept's Flashware Lets Users Try Out Mbone Viewer; Netscape Plug-In Support Also Added,” Cupertino, California, Apr. 15, 1996, 2 pages, downloaded from WWW.
Precept Software Inc.—Press Release “New Version of Precept's IP/TV Video-Distribution Software Delivers Full-Screen, Full-Motion Video To NT Desktops,” Palo Alto, California Aug. 19, 1996, 2 pages, downloaded from WWW.
V. Kumar, “Real-Time Multimedia Broadcasts With the Internet Multicast Backbone,” 8 pages, Jan. 23, 1998, downloaded from WWW.
Precept Software Inc.—Press Release, “Entertainment-Quality Video Comes to Networked Desktops As Precept Adds MPEG Support to IP/TV; Enhanced Browser Plug-In Lets Webmaster Customize Controls,” Palo Alto, California, Jan. 27, 1

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