Classifications

• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
  • H04N21/00—Selective content distribution, e.g. interactive television or video on demand [VOD]
  • H04N21/20—Servers specifically adapted for the distribution of content, e.g. VOD servers; Operations thereof
  • H04N21/23—Processing of content or additional data; Elementary server operations; Server middleware
  • H04N21/236—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
  • H04N21/2365—Multiplexing of several video streams
  • H04N21/23655—Statistical multiplexing, e.g. by controlling the encoder to alter its bitrate to optimize the bandwidth utilization
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
  • H04N19/00—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals
  • H04N19/10—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding
  • H04N19/102—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding characterised by the element, parameter or selection affected or controlled by the adaptive coding
  • H04N19/124—Quantisation
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
  • H04N19/00—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals
  • H04N19/10—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding
  • H04N19/134—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding characterised by the element, parameter or criterion affecting or controlling the adaptive coding
  • H04N19/136—Incoming video signal characteristics or properties
  • H04N19/14—Coding unit complexity, e.g. amount of activity or edge presence estimation
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
  • H04N19/00—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals
  • H04N19/10—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding
  • H04N19/134—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding characterised by the element, parameter or criterion affecting or controlling the adaptive coding
  • H04N19/146—Data rate or code amount at the encoder output
  • H04N19/15—Data rate or code amount at the encoder output by monitoring actual compressed data size at the memory before deciding storage at the transmission buffer
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
  • H04N19/00—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals
  • H04N19/10—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding
  • H04N19/169—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding characterised by the coding unit, i.e. the structural portion or semantic portion of the video signal being the object or the subject of the adaptive coding
  • H04N19/17—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding characterised by the coding unit, i.e. the structural portion or semantic portion of the video signal being the object or the subject of the adaptive coding the unit being an image region, e.g. an object
  • H04N19/172—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding characterised by the coding unit, i.e. the structural portion or semantic portion of the video signal being the object or the subject of the adaptive coding the unit being an image region, e.g. an object the region being a picture, frame or field
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
  • H04N19/00—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals
  • H04N19/60—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using transform coding
  • H04N19/61—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using transform coding in combination with predictive coding
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
  • H04N19/00—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals
  • H04N19/10—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding
  • H04N19/134—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding characterised by the element, parameter or criterion affecting or controlling the adaptive coding
  • H04N19/146—Data rate or code amount at the encoder output

Definitions

• the present invention relates to devices for the real-time transmission of several video programs, each in the form of a binary data stream representing successive frames, on a transmission channel having a determined bit rate capacity, the device comprising, for each program channel supplying a multiplexer attacking the channel, a video coder having a programmable coding rate.
• the document EP-A-0 526 201 describes such a video coder, making it possible to adjust, for each group of blocks of pixels of an image, the quantization step so as to maintain the quality of the image at an approximately value constant.
• weft should be interpreted in a broad sense. It can designate all of the video data necessary to reconstruct a complete image in progressive scanning, all of the data necessary to reconstruct an even or odd frame in interlaced scanning, or even assistance data making it possible to reconstruct an image with from a previous image.
• the invention finds a particularly important, although not exclusive, application in transmission devices according to the MPEG2 video standard, which was the subject of recommendation ITU-TH262 (ISO / IEC) 13818-2 published in June. 1994 by the International Telecommunication Union).
• the MPEG2 standard provides for the implementation of compression algorithms making it possible to generate modifiable bit rate flows for standard resolution images (appendix D.4 to the recommendation above). This possibility is used in particular when coding a delayed-time film for recording on a storage medium.
• Transmission channels have limited capacity.
• the solution used at present when several programs are multiplexed on the same channel consists in defining a priori, for each program, the maximum bit rate which it must apply to the multiplexer. This solution is not very satisfactory because it misuses the resources of the channel.
• the richness of the video information transmitted in each of the programs is very variable. At a given instant, it is statistically probable that at least one coder then has at his disposal a bit rate higher than that which is necessary for him, while another coder will have to apply a compression rate reducing the iconographic quality of the 'image, because it has an insufficient flow.
• the present invention aims in particular to provide a transmission device of the type defined above, responding better than those previously used to the requirements of practice, in particular in that it allows the best use of the capacity of the transmission channel.
• the invention uses the existence of coders making it possible to code each frame at a bit rate different from the previous one. It also uses the fact that we know analyze the information from the coding to determine the iconographic quality of the image obtained.
• the invention therefore proposes a device which comprises: - on each program channel, an image memory having a capacity of at least one frame, placed upstream of the encoder, and an auxiliary encoder receiving the successive input frames at the same time as memory;
• Such a device performs optimal statistical multiplexing, the nature of which is completely different from that of video coding with a quantization step adjusted for each group of blocks to take account of the sensitivity to distortion.
• the MPEG2 standard which provides compressed streams with a bit rate between 2 and 15 Mbits / s in main-main profile, and transmission over a satellite channel
• the most frequent case is that of the transmission of five programs on the same channel.
• the invention will allow, instead of arbitrarily allocating 8 Mbits / s to each program channel, to adapt the bit rate assigned to it at any time to the richness of the image.
• the coded video stream has a suitable bit rate and is then split into packets divided into sequences.
• the description refers to the figure which accompanies it and which is a simplified block diagram, showing a particular mode of implementation of the invention, in the case of a device with two coders supplying the same channel.
• the device the basic structure of which is shown in FIG. 1, comprises two video program channels 10, and 10 2 supplying a multiplexer 12 which attacks modulation and transmission circuits not shown, since they are not concerned by the invention.
• Each program channel comprises, in addition to the video stream, a binary stream representing the sound and a stream of service information. They can be added to the video stream upstream of the multiplexer 12.
• the functions of packetization, multiplexing of the video, sound and service data and of constitution of the queue will be performed in circuits.
• Each program video channel comprises a programmable encoder 16 with variable bit rate, having a compression rate control input 18.
• the video stream to be coded is applied to the variable bit rate encoder 16 by means of a memory of image 20 having a capacity at least equal to one frame.
• Synchronization means not shown, allow writing into memory 20 as the video stream corresponding to a complete frame arrives, and reading from memory with a delay such that the variable bit rate coder 16 receives the stream video with a frame delay.
• Each channel also includes an auxiliary coder 22 which receives the video stream at the same time as the memory 20.
• the auxiliary coder 22 is provided for coding each frame with a fixed bit rate, which will generally be such that the resources allocated to each of the channels are the same. In the case of a satellite channel which can accept a bit rate of 40 Mbits / s, the auxiliary encoder 22 will then be provided for coding each image at the video bit rate compatible with a bit rate on the satellite channel of 8 Mbits / s.
• the auxiliary coder 22 is of a type making it possible to analyze the information resulting from coding and to provide an iconographic quality index. Encoders capable of providing such output information are already known. In particular, an encoder of this type is available from the company C-Cube Microsystems, Milpitas, California. It can also be used as a programmable encoder.
• a first possibility consists in analyzing the average, over the whole of a frame, of the quantization step implemented in the algorithm for passing from the time domain to the frequency domain (algorithm for transformation into discrete cosine in general).
• a given quantization step corresponds to a flow.
• the video coder increases the quantization step during the frame for the groups of pixel blocks concerned, so as not to excessively increase the number of bytes representing the image.
• Analysis of the mean of the final quantization step over a frame makes it possible to know whether the coder would have required a higher bit rate to represent the image satisfactorily and therefore what quality he obtained with the programmed bit rate.
• MPEG2 coding which uses intra-frame coded images (I images) coded without reference to other images, predictively coded images (P images) and images coded by bidirectional prediction (B images).
• I images intra-frame coded images
• P images predictively coded images
• B images images coded by bidirectional prediction
• Another possibility consists in measuring the signal-to-noise ratio between the image before coding and the image after coding. / 01648
• the coding device also includes a processor 26 which receives the iconographic quality indications provided by the two auxiliary coders 22, which play the role of quality estimators.
• the auxiliary coders 22 are provided so that they provide an indication of quality to the processor 26 after a period of time less than the frame repetition period.
• the processor 26 is programmed so as to compare the quality indices it receives either between them or with a reference index. If for example the iconographic qualities of the coded images are comparable, the processor 26 controls the programmable coders 16 so that they use the same compression ratio.
• the processor programs the video coder of the channel having a richness of image requiring a high bit rate for coding by the corresponding coder 16 to be carried out at a bit rate higher than the nominal bit rate.
• the distribution algorithm can be of the same kind as that described in the article by Guha et al already cited. It can be implemented by cable or software.
• the processor 26 and the programmable video coders 16 can in particular be provided to cause coding at a nominal bit rate and at one or two bit rates above and one or two bit rates below the nominal rate, this simple solution being sufficient in most cases.
• the processor 26 must simultaneously have the evaluations provided, each over a complete frame, by the coder estimators 22 of all the program channels. To facilitate this comparison, it is desirable that the video streams are synchronized, by means not shown, so that the frames are in temporal coincidence. However, it is possible to give up synchronization tion, provided there is an image memory of increased capacity upstream of each estimator coder.
• the invention is susceptible of numerous variant embodiments.
• the number of channels can be greater than or less than five.
• the auxiliary coders 22 which serve as estimators can have multiple coding rates rather than just one.
• the different channels can be allocated different resources, which leads to giving the auxiliary encoders 22 different bit rates.
• bit rates can be distributed on the basis of an estimate over a determined number of frames, greater than 1.
• a drawback of this solution is that image memories must be provided upstream of the encoders. It is also possible to ensure such distribution over several frames by storing surpluses or residues of rates at the end of each comparison by the processor 26, and taking them into account on one frame or following frames.

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• Engineering & Computer Science (AREA)
• Multimedia (AREA)
• Signal Processing (AREA)
• Compression Or Coding Systems Of Tv Signals (AREA)

Applications Claiming Priority (3)

Publications (1)

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• 1994
  • 1994-12-13 FR FR9414988A patent/FR2728129A1/fr active Granted
• 1995
  • 1995-12-12 EP EP95942247A patent/EP0800747A1/fr not_active Ceased
  • 1995-12-12 CN CN95197329A patent/CN1173264A/zh active Pending
  • 1995-12-12 AU AU43501/96A patent/AU4350196A/en not_active Abandoned
  • 1995-12-12 WO PCT/FR1995/001648 patent/WO1996019081A1/fr not_active Application Discontinuation
  • 1995-12-12 CA CA002208432A patent/CA2208432A1/fr not_active Abandoned

Non-Patent Citations (1)

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