Pulse or digital communications – Bandwidth reduction or expansion – Television or motion video signal
Reexamination Certificate
2000-09-22
2004-03-23
Lee, Young (Department: 2613)
Pulse or digital communications
Bandwidth reduction or expansion
Television or motion video signal
Reexamination Certificate
active
06711212
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to digital video signal processing, and more particularly, to video communication systems employing transcoding for rate adaptation of video bridging over heterogeneous networks such as multipoint video conferencing, remote collaboration, remote surveillance, video-on-demand, video multicast over heterogeneous networks, and streaming video.
BACKGROUND OF THE INVENTION
Video telephony is an efficient way for business persons, engineers, scientists, etc., to exchange their information at remote locations. With the rapid growth of video telephony, the need for multipoint video conferencing is also growing. A multipoint video conference involves three or more conference participants. In continuous presence video conferencing, each conferee can see all of the other conferees in the same window simultaneously. In such systems, it is necessary to employ a video-bridge to combine the coded video signals from the multiple participants into a single video for display.
FIG. 1
depicts an application scenario of multiple persons participating in a multipoint videoconference with a centralized server. In this scenario, multiple conferees are connected to a central server, referred to as a Multipoint Control Unit (MCU), which coordinates and distributes video and audio streams among multiple participants in a video conference according to the channel bandwidth requirement of each conferee. A video transcoder is included in an MCU to combine the multiple incoming encoded digital video streams from the various conferees into a single coded video bit stream and send the re-encoded video bit-stream back to each participant over the same channel with the required bit rate and format, for decoding and presentation. In the case of a multipoint video conference over the PSTN (Public Switched Telephone Network), e.g. POTS (Plain Old Telephone Service) or ISDN (Integrated Service Digital Network), the channel bandwidth is symmetric. Assuming the conferees have the same channel bandwidth: B Kbps, that is, the MCU receives from the conferees, video at B Kbps each, the MCU combines the video and re-encodes the combined video at B Kbps so as to meet the channel bandwidth requirements for sending back the. video to the conferees. Therefore, it is required to perform bit-rate conversion/reduction at the video transcoder. Bit-rate conversion from high bit-rate to low bit-rate in video transcoding will, however, introduce video quality degradation. The visual quality, the computational load, and the used bit-rates need to be traded off in video transcoding to find a feasible solution.
The simplest approach for implementing the transcoder is the use of open-loop transcoding in which the incoming bit-rate is down-scaled by truncating the DCT coefficients, by performing a re-quantization process, or by selecting an arbitrary number of DCT coefficients. Since the transcoding is done in the coded domain, a simple and fast transcoder is possible. However the open-loop transcoder produces an increasing distortion caused by the “drift” problem due to the mismatched reconstructed picture in the encoder and the decoder. The drift error can be eliminated by cascading a decoder and an encoder. In the cascaded transcoder, the decoder decompresses the incoming bit-stream which was encoded at a bit-rate R1, and then the encoder re-encodes the reconstructed video at a lower bit-rate R2. Although the drift error can be eliminated by using the cascaded transcoder, the computational complexity is very high; thus, direct use of a cascaded transcoder is not practical in real-time applications. The cascaded transcoder's complexity, however, can be significantly reduced by reusing some information extracted from the incoming bit-stream, such as motion information and coding mode information.
Keesman et al. (see reference 6 below) introduced simplified pixel-domain and DCT-domain video transcoders based on a motion vector reuse approach to reduce both the computation cost and the memory cost in a cascaded transcoder; however, in such system, the visual quality is degraded due to the non-optimal motion vector resulting from reusing the incoming motion vectors.
Youn et al. (see references 14 and 15 below) proposed efficient motion vector estimation and refinement schemes which can achieve a visual quality close to that of a cascaded transcoder with full-scale motion estimation with relatively small extra computational cost. Several quantization schemes and efficient transcoding architectures have been proposed in references 6-9 below.
Each of the following background references is incorporated by reference herein.
[1] ITU-T Recommendation H.261, “Video codec for audiovisual services at p×64 kbits/s,” March 1993.
[2] ITU-T Recommendation H.263, “Video coding for low bit-rate communication,” May 1997.
[3] M. D. Polomski, “Video conferencing system with digital transcoding”, U.S. Pat. No. 5,600,646
[4] D. G. Morrison, M. E. Nilsson, and M. Ghanbari, “Reduction of the bit-rate of compressed video while in its coded form,” in Proc. Sixth Int. Workshop Packet Video, Portland, Oreg., September 1994.
[5] Eleftheriadis and D. Anastassiou, “Constrained and general dynamic rate shaping of compressed digital video,” in Proc. IEEE Int. Conf. Image Processing, Washington, D.C., October 1995.
[6] G. Keesman, et al., “Transcoding of MPEG Bitstreams,” Signal Processing Image Comm., vol. 8, pp. 481-500, 1996.
[7] G. Keesman, “Method and device for transcoding a sequence of coded digital signals”, U.S. Pat. No. 5,729,293
[8] H. Sun, W. Kwok, and J. W. Zdepski, “Architectures for MPEG compressed bitstream scaling,”, IEEE Trans. Circuits Syst. Video Technol., vol. 6, pp. 191-199, April 1996.
[9] P. Assuncao and M. Ghanbari, “A frequency-domain video transcoder for dynamic bit-rate reduction of MPEG-2 bit streams,” Trans. On Circuits Syst. Video Technol., vol. 8, no. 8, pp. 953-967, 1998.
[10] M. V. Eyuboglu et al., “Efficient transcoding device and method”, U.S. Pat. No. 5,537,440
[11] Y. Nakajima et al., “Method and apparatus of rate conversion for coded video data”, U.S. Pat. No. 5,657,015
[12] J. Koppelmans et al., “Transcoding device”, U.S. Pat. No. 5,544,266
[13] M. -T. Sun, T. -D. Wu, and J. -N. Hwang, “Dynamic bit allocation in video combining for multipoint video conferencing,” IEEE Trans. Circuit and Systems., vol. 45, no. 5, pp. 644-648, May 1998.
[14] J. Youn, M. -T. Sun, and C. -W. Lin “Motion estimation for high-performance transcoders,” IEEE Trans. Consumer Electronics, vol. 44, pp. 649-658, August 1998.
[15] J. Youn, M. -T. Sun and C. -W. Lin, “Adaptive motion vector refinement for high performance transcoding,” IEEE Trans. Multimedia, vol. 1, no. 1, pp. 30-40 March 1999.
[16] B. Shen, I. K. Sethi, and V. Bhaskaran, “Adaptive motion-vector resampling for compressed video downscaling,” IEEE Trans. Circuits Syst. Video Technol., vol. 9, no. 6, pp. 929-936, September 1999.
[17] ITU-T/SG15, “Video codec test model, TMN8,” Portland, June 1997.
[18] Image Procssing Lab, University of British Columbia, “H.263+ encoder/decoder,” TMN(H.263) codec, February 1998.
SUMMARY OF THE INVENTION
The present invention provides a multipoint video communication system employing a transcoder with a dynamic sub-window skipping technique to enhance the visual quality of the participants of interest. The system firstly identifies the active conferees from the multiple incoming video streams by calculating the temporal and the spatial activities of the conferee sub-windows. The sub-windows of inactive participants are dropped, and the bits saved by the skipping operation are reallocated to the active sub-windows. Several motion vector composition schemes can be used to compose the unavailable motion vectors in the dropped frames due to limited bit-rates or frame-rates of the user clients in video transcoding.
Industrial Technology Research Institute
Lee Young
Stevens Davis Miller & Mosher LLP
LandOfFree
Video transcoder, video transcoding method, and video... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Video transcoder, video transcoding method, and video..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Video transcoder, video transcoding method, and video... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3267668