Pulse or digital communications – Bandwidth reduction or expansion – Television or motion video signal
Reexamination Certificate
1996-12-24
2001-07-17
Le, Vu (Department: 2613)
Pulse or digital communications
Bandwidth reduction or expansion
Television or motion video signal
C348S419100
Reexamination Certificate
active
06263020
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention pertains to a method and apparatus for the compression and transmission of video data. More particularly, the present invention pertains to regulating a transmit buffer in a transmission subsystem and a quantizer selector in a digital video system environment.
A video compression/transmission system that is known in the art is shown in
FIG. 1. A
camera
11
is provided that generates video image data for a video capture component
13
. The video capture component
13
“captures” the video image data from the camera one frame at a time in a known manner and at a predetermined rate (e.g., approximately 30 frames per second). The video capture component
13
transfers the video frame data to a video compressor
15
which may compress the video image data for the frame according to a bit-rate control algorithm. Such a bit-rate control algorithm typically includes a compression algorithm such as any of a variety of block transform based video compression algorithms such as H.261 (International Telecommunication Union—Telecommunications Standardization Sector (“ITU-T”), March, 1993), H.263 (ITU-T, Dec. 5, 1995), JPEG (“Joint Photographic Expert Group”)(International Organization for Standardization/International Electrotechnical Commission (“ISO/IEC”) 10918-1), MPEG-I and MPEG-II (“Motion Picture Expert Group”)(ISO/IEC 11172-2 and 13818-2). The compressed video frame data is then sent to a transmitter
19
via a video controller
17
, and the data is stored temporarily in a transmit buffer
20
under the control of a buffer regulator. The transmitter
19
then pulls data from the transmit buffer sequentially and adds the appropriate protocol information and transmits the data to a transmission medium
21
(e.g., POTS (Plain Old Telephone Service)).
In systems, such as ProShare® systems and Intel Smart Video Recorder® systems (Intel Corporation, Santa Clara, Calif.), the bit rate control algorithm of compressor
15
operates separately from the transfer of data from transmit buffer
20
to transmission medium
21
by the buffer regulator. Because of this separation, the operation of the bit rate control algorithm can only estimate the state of the transmit buffer
20
(i.e., how much data is contained in the transmit buffer
20
). Also, the buffer regulator of the transmitter
19
typically requires that the video compressor
15
produce the same amount of compressed data for each frame. This separation leads to inaccuracies in that the transmit buffer
20
is incorrectly filled (i.e., not filled with enough data which reduces the frame rate over the transmission medium
21
or filled with too much data causing delay or latency).
SUMMARY OF THE INVENTION
According to a first embodiment of the present invention, the video compressor receives a succession of video frames, each frame including uncompressed video frame data divided into N macroblocks, where each macroblock defines a spatial area of each of the frames. The video compressor compresses a macroblock of video frame data based on a quantization parameter, which is supplied by a quantizer selector of a bit rate controller. The quantizer selector calculates the quantization parameter for an nth one of the macroblocks of a current video frame based on a cumulative amount of compressed video image data generated for the first n-lmacroblocks of the current frame and a previous frame. Since the quantization parameter has a direct effect on the number of compressed bits generated per macroblock, the bit rate controller can control the total number of compressed bits generated for a frame on a macroblock-by-macroblock basis.
According to a second embodiment of the present invention, a video compressor generates compressed video frame data to be sent to a transmit buffer (which, in turn, are sent over a transmission medium). The video compressor operates under the control of a buffer regulator of the bit rate controller which schedules the compression of video frames captured by a video capture component coupled to the video compressor. When the number of bits remaining in the transmit buffer falls below a threshold, the buffer regulator schedules a compression of a new frame from the video capture component. In this manner, the effective bandwidth of the transmission medium is used efficiently in that compressed video frame data is sent to the transmit buffer as the data is needed.
REFERENCES:
patent: 5038209 (1991-08-01), Hang
patent: 5412431 (1995-05-01), Vogel
patent: 5459515 (1995-10-01), Chevance et al.
patent: 5489943 (1996-02-01), Kutner
patent: 5691770 (1997-11-01), Keesman et al.
patent: 5710595 (1998-01-01), Hang et al.
patent: 5777680 (1998-07-01), Kim
Chen et al, “A self-governing rate buffer control strategy for pseudoconstant bit rate video coding”, IEEE Transaction on Image Processing, vol. 2, Iss. 1, Jan. 1993, pp. 50-59.*
Video CODEC Test Model, TMN5; ITU Telecommunication Standardization Sector Study Group 15, Working Party 15/I Expert's Group on Very Low Bitrate Visual Telephony,; Source: Telenor Research (TR); Jan. 31, 1995.
ITU-T, Video Coding for Low Bitrate Communication, Draft H.263, Dec. 5, 1995.
ITU-T, Video CODEC for Audiovisual Services at p×64 kbits, H.261, Mar., 1993.
Brucks Doug
Gardos Thomas R.
Gutmann Michael J.
Ing Stephen
Lillevold Karl O.
Intel Corporation
Kenyon & Kenyon
Le Vu
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