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WO2007066101A2 - Appareil de commande d'un codeur et procede associe - Google Patents

Appareil de commande d'un codeur et procede associe Download PDF

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Publication number
WO2007066101A2
WO2007066101A2 PCT/GB2006/004551 GB2006004551W WO2007066101A2 WO 2007066101 A2 WO2007066101 A2 WO 2007066101A2 GB 2006004551 W GB2006004551 W GB 2006004551W WO 2007066101 A2 WO2007066101 A2 WO 2007066101A2
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WO
WIPO (PCT)
Prior art keywords
coding unit
encoding
encoder
video coding
time
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Ceased
Application number
PCT/GB2006/004551
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English (en)
Other versions
WO2007066101A3 (fr
Inventor
Chaminda Sampath Kannangara
Ian Richardson
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Robert Gordon University
Original Assignee
Robert Gordon University
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Robert Gordon University filed Critical Robert Gordon University
Publication of WO2007066101A2 publication Critical patent/WO2007066101A2/fr
Publication of WO2007066101A3 publication Critical patent/WO2007066101A3/fr
Anticipated expiration legal-status Critical
Ceased legal-status Critical Current

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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
    • H04N19/189—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding characterised by the adaptation method, adaptation tool or adaptation type used for the adaptive coding
    • H04N19/19—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding characterised by the adaptation method, adaptation tool or adaptation type used for the adaptive coding using optimisation based on Lagrange multipliers
    • 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
    • H04N19/132—Sampling, masking or truncation of coding units, e.g. adaptive resampling, frame skipping, frame interpolation or high-frequency transform coefficient masking
    • 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
    • H04N19/152—Data rate or code amount at the encoder output by measuring the fullness of 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
    • H04N19/134—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
    • H04N19/156—Availability of hardware or computational resources, e.g. encoding based on power-saving criteria
    • 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

Definitions

  • the present invention relates to an encoder control apparatus configured to control a video encoder and a method of controlling a video encoder.
  • the encoding of video streams in real time normally makes significant demands on the processing capabilities of the video encoder and its associated electronic hardware.
  • battery powered mobile devices having a video encoding capability such as personal digital assistants (PDA's) and mobile telephones
  • power consumption depends on processor utilisation which, in turn, has an impact on the rate at which the battery is discharged.
  • the encoding of macroblocks of a video stream is normally a computationally intensive task. In known apparatus, a macroblock may be skipped after the motion estimation step of the encoding process. However, doing so
  • WO 04056125 describes a method of predicting whether or not the motion estimator will skip a macroblock before making a decision on whether or not the xnacroblock is to be processed by the motion estimator.
  • the method of WO 04056125 involves estimating the contribution that the macroblock will make to the video quality and making a decision based on estimation.
  • the inventors have realised that although the approach of WO 04056125 can provide for an improvement in processor resource utilisation, further improvements can be
  • the present invention has been devised in the light of this realisation. It is therefore an object of the present invention to provide an encoder control apparatus that is configured to control an encoder to take account of a computational burden to be placed on a signal processing component when processing a video coding unit, such as a macroblock. It is a further object of the present invention to provide a method of controlling a encoder to take account of a computational burden to be placed on a signal processing component when processing a video coding unit, such as a macroblock.
  • an encoder control apparatus configured to control an encoder, the encoder being operable to encode a video coding unit in accordance with one of a plurality of encoding strategies, the plurality of encoding strategies imposing respectively different computational burdens
  • the encoder control apparatus comprising a controller configured to generate a control output in dependence upon a target value, the target value corresponding to a computational burden to be placed on a signal processing component when processing the video coding unit, the control output, in use, being provided to the encoder to select one of the plurality of encoding strategies, whereby the encoder encodes the video coding unit in accordance with the selected
  • the encoder is of a kind that has the capability to encode a video coding unit in accordance with one of a plurality of encoding strategies. More specifically, the plurality of encoding strategies may comprise: encoding the video coding unit fully; and not encoding (i.e.
  • the selection between encoding the video coding unit fully and not encoding the video coding unit is made in dependence upon the control output generated by the encoder control apparatus, with the control output depending on the target value.
  • apparatus may be operative to change the target value from one video coding unit to another video coding unit.
  • the target value may correspond to a computational burden to be placed on a signal processing component which will process the video coding unit after the video coding unit is encoded by the encoder.
  • apparatus may be operable to take account of a
  • the signal processing component may comprise at least one of: a transcoder and a decoder.
  • the target value may correspond to a computational burden to be placed on the encoder when encoding the video coding unit.
  • the target value may be based on a characteristic of the video coding unit, such as a number of macroblocks to be coded. More specifically, the characteristic may comprise at least one of: a predicted time to encode the video coding unit; and a number of macroblocks in the video coding unit.
  • the target value may be based on a characteristic of the signal processing component. For example, the characteristic may be a measure of a capability of the signal processing
  • the characteristic of the signal processing component may comprise a number of
  • the target value may be based upon a characteristic of a previously encoded video coding unit. More specifically, the characteristic of the previously encoded video coding unit may comprise a length of time to encode the previous video coding unit .
  • the encoder control apparatus may comprise an encoding time calculator which is operative to determine a coding unit encoding time representative of a length of time to encode a previous video coding unit.
  • the target value may comprise a predetermined value set by a user of the encoder control apparatus.
  • the target value may be based on a predicted time to encode the video coding unit and the predicted time may be based upon a length of time to encode a previous video encoding unit.
  • the control output may comprise a previous control output added to an encoding complexity weighting value, that is:
  • the encoding complexity weighting value may be determined by a ratio of the change in encoding complexity weighting value from a previous coding unit and the resultant change in the coding unit encoding time.
  • the encoding complexity weighting value may be:
  • the control output may be limited to avoid a reduction in computational burden below a predetermined level .
  • the predetermined level may represent a maximum acceptable distortion of the coding unit to be encoded by the encoder.
  • the encoder control apparatus may further comprise a buffer operative to store a plurality of video coding units to be encoded. More specifically, the encoder control apparatus may further comprise a buffer level controller operative to monitor a level of the buffer. The buffer level may be a measure of the available buffer capacity.
  • the buffer level controller may be operative to determine the target value in dependence on the buffer level. More specifically, the buffer level controller may be operative to determine a target coding unit encoding time in dependence upon the buffer level, the coding unit encoding time and a predetermined target coding unit rate. More specifically, encoder control apparatus may be operative to calculate the target coding unit encoding time as follows:
  • T f is the target coding unit interval
  • T c is the time at the start of encoding the current coding unit
  • T ⁇ is the time that the last coding unit entered the buffer
  • B is the buffer capacity
  • Buff is the buffer level at the time of calculation. More specifically, when the buffer level is zero, the target coding unit encoding time may be equal to the target coding unit interval. Alternatively or in addition, when the target coding unit encoding time is less than a predetermined minimum coding unit encoding time, the buffer level controller may flush the current coding unit from the buffer.
  • the coding unit may be a whole or subset of at least one of the following: a video frame; an interlaced field; and a slice.
  • an encoder control apparatus configured to control an encoder, the encoder being operable to encode a video coding unit in accordance with one of a plurality of encoding strategies, the plurality of encoding strategies imposing respectively different computational burdens on the encoder, the encoder control apparatus comprising a controller configured to generate a control output in dependence upon a target value, the target value corresponding to a computational burden to be placed on the encoder when encoding the video coding unit, the control output, in use, being provided to the encoder to select one of the plurality of encoding strategies, whereby the encoder encodes the video coding unit in accordance with the selected
  • Embodiments of the second aspect of the present invention may comprise one or more of the features of the first aspect of the present invention.
  • an encoder apparatus comprising an encoder control apparatus according to the first or second aspect of the present invention and an encoder which is configured to receive the control output from the encoder control apparatus.
  • Embodiments of the third aspect of the present invention may comprise one or more of the features of the first aspect of the present invention.
  • a battery powered device e.g. a PDA or a mobile telephone
  • Embodiments of the fourth aspect of the present invention may comprise one or more of the features of the first aspect of the present invention.
  • a fifth aspect of the present invention there is provided a method of controlling an encoder, the coder being operable to encode a video coding unit in accordance with one of a plurality of encoding
  • Embodiments of the fifth aspect of the present invention may comprise one or more features of the first or third aspects of the present invention. According to a further aspect of the present invention there is provided an encoder control system for
  • a video coding unit may be a complete video frame, one or more interlaced fields, one or more slices or a subset of one or more of these. Any derivation of a video sequence which may require compression can be defined as a video coding unit or coding unit .
  • an encoding complexity value is modified for each video coding unit.
  • the encoding complexity value ⁇ c may be a multiplier associated with Lagrangian
  • the encoding target value comprises a coding unit target encoding time.
  • the encoding target value may alternatively be a target number of coded macroblocks in each video coding unit, a target number of processor instructions or other values which may affect the
  • the encoding complexity weighting value is determined by a ratio of the change in encoding
  • the system further comprises a buffer having a buffer capacity and a buffer level controller, wherein the buffer stores coding units to be processed and the buffer level controller monitors the buffer capacity, determines a buffer level, and determines the target coding unit encoding time on the basis of the buffer level, the coding unit encoding time and a predetermined target coding unit rate.
  • a buffer having a buffer capacity and a buffer level controller, wherein the buffer stores coding units to be processed and the buffer level controller monitors the buffer capacity, determines a buffer level, and determines the target coding unit encoding time on the basis of the buffer level, the coding unit encoding time and a predetermined target coding unit rate.
  • a method of controlling an encoder for encoding a stream of video coding units in accordance with an encoding complexity function comprising the step of generating an encoding complexity value for input to the encoding complexity function, on the basis of an encoding target value, altering the complexity required to encode the video coding unit being encoded at that time and, thereby, the length of time the encoder takes to encode that video coding unit.
  • the step of modifying an encoding complexity value is completed for each coding unit.
  • the encoding target value comprises a coding unit target encoding time.
  • the encoding target value may alternatively be a target number of coded macroblocks in each video coding unit, a target number of processor instructions or other values which may affect the complexity required to encode the video coding unit.
  • the current encoding complexity value is a previous coding unit's encoding complexity value added to an encoding complexity weighting value, that is:
  • the method further comprises the step of calculating a coding unit encoding time, representing the length of time to encode a previous coding unit.
  • the encoding complexity weighting value is determined by a ratio of the change in encoding
  • the encoding complexity weighting value is:
  • the method further comprises the steps of storing one or more coding units to be encoded in a buffer having a buffer capacity and controlling the amount of coding units stored by monitoring the number of coding units stored, determining a buffer level, and determining the target coding unit encoding time on the basis of the number of coding units stored, the coding unit encoding time and a predetermined target coding unit rate.
  • T" is the target coding unit encoding time
  • T f is the target coding unit interval
  • T c is the time at the start of encoding the current coding unit
  • Ti is the time that the last coding unit entered the buffer
  • B is the buffer total capacity
  • Buff is the buffer level.
  • the target coding unit encoding time is equal to the target coding unit interval.
  • the method performs the step of flushing the current coding unit from the buffer.
  • the coding unit is a whole or subset of one or more of the " following: a video frame; an interlaced field; or a slice.
  • a device comprising a processor and an encoder control system according to the first aspect of the present invention.
  • the device can alter the target coding unit encoding time to reduce the processor usage.
  • the device is a battery powered device and the processor usage is reduced to conserve battery life. Processor usage within the device may be restricted, for example, due to other processes requiring to be serviced by the processor and/or limited battery power in mobile devices.
  • FIG. 1 illustrates a device incorporating an encoder control system according to the present invention
  • Fig. 2 illustrates a table comparing video frame rate and peak signal to noise ratio (PSNR) for a prior art encoder and an encoder managed by an encoder control system of the present invention
  • Fig. 3 illustrates a graph of a degradation category rating test comparing an encoder managed by an encoder control system of the present invention and a standard encoder without management at various levels of
  • PSNR peak signal to noise ratio
  • Fig. 4 illustrates a graph of a degradation category rating test comparing an encoder managed by an encoder control system of the present invention and a standard encoder without management at various levels of
  • Fig. 5 illustrates a graph of a pair comparison test comparing an encoder managed by an encoder control system of the present invention and a standard encoder without management at the same levels of complexity and the same bit rate.
  • the present invention provides for an acceptable video coding unit rate where available processing resources are limited.
  • a conventional video encoder will typically choose to skip coding units in order to meet real-time encoding constraints.
  • the remaining description refers specifically to frames as the video coding unit and to other parameters in terms of frames rather than video coding units.
  • the video coding unit could be any derivation of a video sequence which ( requires to be encoded.
  • the video coding unit could be one or more fields, one or more slices or a subset of one or more of these.
  • a video capture device 10 comprises a video camera or other video source 12, an encoder 14, an encoder control system 16 (which constitutes an encoder control apparatus according to the present invention) and a means for setting a target coding unit rate, which in this case is a target frame rate 18.
  • the encoder control system 16 comprises a buffer 20, a buffer level controller 22 and a complexity controller 24 (which constitutes a controller) .
  • the target frame rate 18 is passed to the video camera 12 and the buffer level controller 22.
  • the video camera 12 begins to capture video frames at the target frame rate 18 and passes them to the buffer 20.
  • the buffer 20 passes video frames to the encoder 14 as soon as the encoder 14 can accept them.
  • the encoder 14 comprises an encoding complexity function which varies the level of complexity of the current frame (i.e. the computational burden involved in encoding the frame).
  • the encoding complexity function provides the means by which to select one of a plurality of encoding strategies for the encoder.
  • the encoder 20 uses a method that predicts which macroblocks in a frame can be skipped prior to the computationally intensive step of motion estimation by deciding whether the statistics of a macroblock are greater than a particular threshold level, as described in WO 04056125.
  • the complexity controller 24 calculates encoding
  • ⁇ c (which constitutes a control output) which is provided to the encoder 14.
  • the encoding complexity value ⁇ c would be added to the statistics to increase the likelihood that the macroblock would be skipped if the complexity of the frame is required to be reduced.
  • the Lagrangian rate- distortion-complexity costs of coding or skipping a macroblock may be defined as:
  • ⁇ r and ⁇ c are Lagrange multipliers associated with rate and complexity. Note that the rate associated with a skipped macroblock is effectively zero and the computational complexity associated with a macroblock identified as "skipped" prior to coding is negligible, since no further processing is carried out. It is assumed that the computational complexity of all coded macroblocks is roughly the same, hence C(Mi) ⁇ 1- The i th macroblock should be skipped (not coded) if:
  • the complexity controller 24 chooses the encoding
  • a target coding unit encoding time T" which in this case is a target frame encoding time, is supplied by the buffer level controller 22.
  • This adaptive proportional feed back mechanism allows for changing source statistics, that is, the content of the video frames changing, for example, due to a change in the amount of motion and/or detail in the scene.
  • the encoding complexity weighting value ⁇ c is the ratio between the change in Lagrange multiplier and the
  • the encoding complexity value ⁇ > may be derived from a complexity reduction target C ⁇ as follows, where C ⁇ is the complexity reduction as a proportion of full complexity.
  • the first encoding complexity value ⁇ £ is initialised to zero at the start of the encoding process to be used for the first frame.
  • the encoding complexity weighting value ⁇ c is bounded by the limits 1 and -2.
  • the encoding complexity value ⁇ c (n) affects the complexity of the current frame by controlling how the encoder 14 analyses the current frame. For example, in the method of WO04056125, the encoding complexity value ⁇ ( c n) controls the number of skipped macroblocks .
  • the buffer level controller 22 is controlling the target frame encoding time T" , the buffer level controller 22
  • the time Ti is passed to the buffer level controller 22 and the buffer level Buff is incremented.
  • the time T c is passed to the buffer level controller 22 and the buffer level Buff is decremented, before calculating the target frame encoding time for the next frame. Assuming that buffer space of the frame currently being encoded will not be freed until the frame is completely coded, the "total delay" in frame processing at the beginning of encoding a frame can be calculated as:
  • Total _ Delay T C -T 1 + T f (Buff -1) .
  • a linear model for the target frame encoding time T n can be defined as follows:
  • a second constraint may be imposed after calculating equation (6) as if T n ⁇ TH frame _ skip , where TH fmme _ skip is a predetermined threshold level, then a frame should be skipped by removing it from the buffer and going to the next frame .
  • the complexity controller 24 can then control the computational complexity of the next frame .
  • Limit ⁇ c and TH fmme _ skjp act as control parameters affecting the compromise between frame quality and frame rate . It should be noted than Limit ⁇ c has a more significant effect than TH frame _ skip . Referring to Fig.
  • a table is shown containing a comparison of a prior art "normal” encoder with that of an encoder controlled by the present invention (under the heading "Managed Complexity Encoder") .
  • the basic coding unit is one video frame.
  • the table lists the achieved frame rate and the average Peak Signal-to-Noise Ratio (PSNR) of a series of video stream with varying complexity.
  • PSNR Peak Signal-to-Noise Ratio
  • Fig. 3, Fig. 4 and Fig. 5 have a sequence number on the x-axis which refers to the video streams as numbered in Table 1.
  • the y-axis is labelled MOS, referring to Mean Opinion Score (as defined by ITU-T Standard P.910).
  • MOS Mean Opinion Score
  • the overall rate of the prior art encoder is less than the managed complexity encoder due to the large difference in frame rate.
  • the prior art encoder was used at lower QP values than Managed complexity, so that both overall Bit rate and Complexity were the same for both Normal and Managed complexity encoders .
  • Both Fig. 4 and Fig. 5 show that even when per-frame PSNR is significantly increased by the prior art encoder, there is significant evidence that users prefer higher frame rate video achieved by the managed complexity encoder as opposed to lower frame rate video with higher frame quality. As such, the present invention allows a higher encoding frame rate to be maintained through the use of
  • the encoding complexity may be determined in dependence on a target coding unit rate which takes account of a
  • Such another signal processing component may be a transcoder or an encoder, which may, for example, present a processing "bottleneck" to an encoded video coding unit.
  • the "bottleneck" may be taken account of by selecting an encoding strategy that reduces the computational burden borne by the signal processing component when the encoded video coding unit is processed by the signal processing component.

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

Abstract

L'invention porte sur l'appareil (16) de commande d'un codeur vidéo (14) pouvant coder une unité de codage vidéo en suivant une parmi plusieurs stratégies de codage imposant respectivement différentes charges de calcul. Ledit appareil comporte un contrôleur (24) produisant des instructions de commande en fonction d'une valeur cible correspondant à la charge de calcul attribuée à un élément de traitement de signaux lors du traitement de l'unité de codage vidéo. Les instructions de commande de l'appareil transmises au codeur sélectionnent l'une des stratégies de codage et le codeur code l'unité de codage vidéo en fonction de la stratégie de codage sélectionnée.
PCT/GB2006/004551 2005-12-05 2006-12-05 Appareil de commande d'un codeur et procede associe Ceased WO2007066101A2 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
GB0524663A GB2432985A (en) 2005-12-05 2005-12-05 Encoder control system based on a target encoding value
GB0524663.2 2005-12-05

Publications (2)

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WO2007066101A2 true WO2007066101A2 (fr) 2007-06-14
WO2007066101A3 WO2007066101A3 (fr) 2007-08-16

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JP3748717B2 (ja) * 1998-08-31 2006-02-22 シャープ株式会社 動画像符号化装置
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GB2432985A (en) 2007-06-06
GB0524663D0 (en) 2006-01-11

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