Classifications

• • 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
  • H04N19/154—Measured or subjectively estimated visual quality after decoding, e.g. measurement of distortion
• • 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 coding an input video stream representing successive frames by representation of each frame by a different amount of information from frame to frame, of the type comprising a video coder with programmable bit 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 from a previous image.
• the invention finds a particularly important application constituted by devices intended to transfer a video program to a storage medium having a limited capacity.
• an opto-electronic disc known as a CD-ROM
• CD-ROM can only store a complete film of normal duration, approximately 120 minutes, with a coding speed of 3 Mbits / s.
• an encoder is used whose output rate is the average rate corresponding to the capacity of the support. This solution is not very satisfactory, because the richness of the image varies considerably, either by the abundance of details, or by the degree of correlation between successive images of the same sequence, which determines the possibilities of prediction from frame to frame.
• the present invention aims in particular to provide a device of the type defined above which better meets those previously used to the requirements of practice, in particular in that it allows the best use of the capacity of a storage medium.
• 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 how to analyze the information coming from the coding to determine the iconographic quality of the coded image.
• the invention therefore proposes a device which comprises:
• a second encoder of fixed bit rate, receiving the input video stream
• 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.
• control means are provided so that the average coding rate has a value compatible with the capacity of the support.
• a memory is provided in the comparison means for initially storing the available capacity and the number of frames to be recorded.
• the control means can deduce therefrom an average bit rate to be respected and modulate the bit rate of the encoder while keeping the required average value over successive periods, for example of a few minutes.
• the memory can be gradually decremented so that the remaining storage time is always available.
• the control means can adjust the average flow rate around which the subsequent modulation takes place.
• a simpler solution consists in fixing a priori the average flow.
• the device which is a simplified block diagram showing a particular embodiment of the invention.
• the device comprises a program channel 10 which receives, in addition to the video stream, a binary stream representing the sound and a stream of service information, to be added to the video stream.
• a program channel 10 which receives, in addition to the video stream, a binary stream representing the sound and a stream of service information, to be added to the video stream.
• the functions of packetization, multiplexing of video data, sound and service, and creation of a queue are performed in circuits 14 which it is not necessary to describe here, because they can be of known type.
• the program video channel comprises a variable rate programmable encoder 16, having a compression rate control input 18.
• the video stream to be encoded is applied to the variable rate encoder 16 via a memory image 20 having a capacity at least equal to one frame.
• Synchronization means not shown allow writing to memory 20 as and when the arrival of the video stream corresponding to a complete frame, and the reading in memory with a delay such that the variable rate coder 16 receives the video stream with a delay of a frame.
• An auxiliary encoder 22 receives the video stream at the same time as the memory 20.
• the auxiliary encoder 22 is provided for encoding each frame with a fixed bit rate, which will generally be close to the maximum admissible average bit rate, for example 3 Mbit / s for the storage of a film on an opto-electronic disc or CD-ROM.
• the auxiliary coder 22 has only an estimator role: it provides, on an output 24, coding quality estimation information, * since it is supplied with a frame advance on the programmable coder , it is able to provide information concerning the frame being stored, provided that its calculation time is less than the duration of a frame.
• a processor 26 analyzes the result and controls the programmable coder 16 to fix the bit rate at a value linked to the needs of the image; in the example above, the processor compares the iconographic quality estimate supplied by the 3 Mbits / s auxiliary encoder with a reference or nominal value. If the nominal value is exceeded, the processor commands a reduction in flow. Otherwise, it programs the programmable video encoder with a bit rate setpoint greater than 3 Mbits / s, insofar as this increase is compatible with the average bit rate to be observed so as not to overflow the support, while optimizing its use. .
• the auxiliary coder 22 is of a type making it possible to analyze the information resulting from the coding and to provide an index of iconographic quality. 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, Califor- nie. 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 pixels concerned, so as not to excessively increase the number of bytes representing the image.
• 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
• the processor 26 and the programmable video coder 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 invention is susceptible of numerous variant embodiments.
• the auxiliary encoder 22 which serves as an estimator may in particular have a coding rate which does not correspond to the average available rate.

Landscapes

• Engineering & Computer Science (AREA)
• Multimedia (AREA)
• Signal Processing (AREA)
• Compression Or Coding Systems Of Tv Signals (AREA)
• Compression, Expansion, Code Conversion, And Decoders (AREA)

Priority Applications (2)

Applications Claiming Priority (2)

Publications (1)

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Cited By (2)

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Citations (3)

• 1994
  • 1994-12-13 FR FR9414986A patent/FR2728130A1/fr active Granted
• 1995
  • 1995-12-12 AU AU43500/96A patent/AU4350096A/en not_active Abandoned
  • 1995-12-12 CN CN 95197330 patent/CN1173263A/zh active Pending
  • 1995-12-12 WO PCT/FR1995/001647 patent/WO1996019080A1/fr not_active Application Discontinuation
  • 1995-12-12 EP EP95942246A patent/EP0800746A1/fr not_active Withdrawn
  • 1995-12-12 CA CA 2207447 patent/CA2207447A1/fr not_active Abandoned

Patent Citations (3)

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