Buffer control for variable bit-rate channel

• US 5,159,447 A
• Filed: 05/23/1991
• Issued: 10/27/1992
• Est. Priority Date: 05/23/1991
• Status: Expired due to Term

• Current Assignee: American Telephone & Telegraph Company (AT&T, Inc.)
• Original Assignee: AT&T, Inc.
• Inventors: Haskell, Barin G., Reibman, Amy R.
• Primary Examiner(s): Groody, James J.
• Assistant Examiner(s): LEE, MICHAEL
• Application Number:
  US07/704,551
• Time in Patent Office: 523 Days
• Field of Search: 358/133, 358/135, 358/136, 358/105, 358/141, 358/142, 358/12, 375/27, 375/28, 375/26, 370/84, 370/85.7, 370/95.1
• US Class Current: 375/240.05
• CPC Class Codes: H04J 3/1688 the demands of the users being taken into account after redundancy removal, e.g. by predictive coding, by variable sampling reducing bandwidth of signals in general H04B1/66; in PCM-systems H04B14/046; removal of redundancy in telegraph communication H03M7/30
• CPC Class Codes: H04L 2012/5678 Traffic aspects, e.g. arbitration, load balancing, smoothing, buffer management
• CPC Class Codes: H04N 19/152 by measuring the fullness of the transmission buffer
• CPC Class Codes: H04N 19/30 using hierarchical techniques, e.g. scalability H04N19/63 takes precedence
• CPC Class Codes: H04N 19/50 using predictive coding H04N19/61 takes precedence
• CPC Class Codes: H04N 21/23406 involving management of server-side video buffer
• CPC Class Codes: H04N 21/236 Assembling of a multiplex stream, e.g. transport stream, by combining a video stream with other content or additional data, e.g. inserting a URL [Uniform Resource Locator] into a video stream, multiplexing software data into a video stream; Remultiplexing of multiplex streams; Insertion of stuffing bits into the multiplex stream, e.g. to obtain a constant bit-rate; Assembling of a packetised elementary stream multiplexing of data packets for data networks, e.g. RTP/UDP H04L65/00
• CPC Class Codes: H04N 21/2401 Monitoring of the client buffer
• CPC Class Codes: H04N 21/2402 Monitoring of the downstream path of the transmission network, e.g. bandwidth available traffic monitoring in data switching networks H04L43/00; monitoring data switching networks utilization H04L43/0876
• CPC Class Codes: H04N 21/2662 Controlling the complexity of the video stream, e.g. by scaling the resolution or bitrate of the video stream based on the client capabilities
• CPC Class Codes: H04Q 11/0478 Provisions for broadband connections

Abstract

The problems of buffer overflow and underflow encountered when employing actually variable or effectively variable bit-rate channels for communicating encoded video images are overcome by jointly controlling the number of bits employed to encode each video frame and the transmission bit-rate of the variable bit-rate channel as experience by the encoder. The selection of the number of bits employed to encode each video frame, and hence the encoder bit-rate, as well as the associated channel bit-rate are determined from the encoder buffer fullness, a determination of the decoder buffer fullness and any constraint imposed on the channel. The encoder is responsive to the selected encoder bit-rate and accordingly adjusts its encoding parameters so as to achieve the selected encoder bit-rate.

Claims

1. A method for controlling at least one variable rate encoder which is receiving a signal as an input and is adapted for supplying a variable bit-rate encoded version of said signal as an output via an encoder buffer to a channel having an variable transmission rate for said encoded output, said channel transporting said encoded version of said signal to at least one decoder via an at least one decoder buffer, comprising the steps of:

monitoring a fullness indication of said at least one encoder buffer;

monitoring a fullness indication of said at least one decoder buffer;

developing estimates for a plurality of future transmission capacity for said channel;

making a request to said channel for a current transmission capacity;

making a determination as to an actual transmission capacity made available by said channel in response to said request;

developing at least one control signal, in response to said estimates of future transmission rates, said request, said fullness indication of said at least one encoder buffer and said fullness indication of said at least one decoder buffer for controlling said variable bit-rate of said encoded version of said signal supplied by said at least one variable rate encoder such that overflow or underflow of at least one encoder buffer and at least one decoder buffer is avoided.

2. The method as defined in claim 1 wherein said at least one control signal specifies at least one range of acceptable bit-rates that can be supplied by said at least one variable rate encoder.

3. Apparatus in an encoder unit for encoding an original video signal including frames, wherein each frame contains at least one image representation, and for supplying as an output for transmission, to a variable bit-rate channel, an encoded version of said original video signal including encoded frames containing at least one encoded image representation, the variable bit-rate channel being adapted for supplying said encoded version of said original video signal to a remote decoder unit including at least one decoder buffer for storing the encoded version of the original video signal and at least one video decoder for generating a reconstructed version of the original video signal, the apparatus comprising:

means for encoding each of said frames of said original video signal into a first encoded version in which each frame of said original video signal is represented by a plurality of bits, the actual number of said bits for each frame being within a predetermined range, each of said first encoded frames being supplied as an output as a first encoded version of said original video signal;

encoder buffer means for storing said first encoded version of said original video signal and for supplying as an output each frame of said first encoded version of said original video signal;

means for generating a second encoded frame for each frame of said first encoded version of said original video signal by removing therefrom a predetermined number of bits and supplying said second encoded version of each frame of said original video signal as said encoded version of said original video signal comprising encoded frames for transmission;

means for generating bit-rate requests for a current frame to be supplied to said channel;

means for generating a set of estimated transmission rates that are expected to be supplied by said channel for a predetermined number of future frames of said encoded version of said original video signal;

means, responsive to an actual number of bits within at least one frame of said first encoded version of said original video signal and said set of estimated transmission rates, for developing said range such that overflow or underflow of said encoder buffer means and said at least one decoder buffer is avoided.

4. The apparatus as defined in claim 3 wherein said means for requesting from said channel a transmission rate for transmitting a current frame is responsive to said actual number of bits within at least one frame of said first encoded version of said original video signal and at least one transmission rate granted by said channel.

5. The apparatus as defined in claim 3 wherein said means for generating said set of estimated transmission rates is responsive to said actual number of bits within at least one frame of said first encoded version of said original video signal and at least one transmission rate granted by said channel.

6. Apparatus for use in an encoder unit that encodes a plurality of signals each of which includes access units, each of said access units contains at least a predetermined amount of information and each signal of said plurality of signals is independent of any other signal in said plurality, said encoder unit supplying as an output for transmission, to a fixed bit-rate channel, an encoded version of each signal of said plurality in a multiplexed format, said channel adapted for supplying said encoded versions of said signals in said multiplexed format to a decoder unit including at least one decoder buffer for temporarily storing at least one of said encoded versions of said plurality of signals and at least one video decoder for generating a reconstructed version of at least one of said plurality of signals from said at least one temporarily stored signal, said apparatus comprising:

a plurality of means for encoding each access unit of each signal of said plurality into at least one packet, each access unit being represented in said packets by a plurality of bits, the actual number of said bits employed for representing a particular access unit being within a predetermined range for the particular signal of said plurality which includes the particular access unit, each of said packets being supplied as an output and each one of said means for encoding being dedicated to a particular signal of said plurality of signals;

a plurality of buffer means, each for receiving, temporarily storing and supplying as an output packets supplied from one of said means for encoding;

multiplexing means for combining, in multiplexed fashion, packets supplied as outputs from said plurality of buffer means;

buffer means for receiving, temporarily storing and supplying as an output to said fixed bit-rate channel said packets combined in multiplexed fashion; and

controller means for specifying for each of said means for encoding said predetermined range and for coordinating and controlling said multiplexer means such that overflow or underflow of any of said buffer means that temporarily store any representation of said access units in said encoder or said decoder is avoided.