Digital Video Transcoding
JUN XIN,MEMBER,IEEE,CHIA-WEN LIN,SENIOR MEMBER,IEEE,AND MING-TING SUN,FELLOW,IEEE
Invited Paper
Video transcoding,due to its high practical values for a wide range of networked video applications,has become an active research topic.In this paper,we outline the technical issues and research results related to video transcoding.We also discuss tech-niques for reducing the complexity,and techniques for improving the video quality,by exploiting the information extracted from the input video bit stream.
Keywords—Error resilience,motion estimation,rate control, transcoding architecture,video transcoding.
I.I NTRODUCTION
Video transcoding is the operation of converting a video from one format into another format.A format is de?ned by such characteristics as the bit rate,frame rate,spatial resolu-tion,coding syntax,and content,as shown in Fig.1.
One of the earliest applications of transcoding is to adapt the bit rate of a precompressed video stream to a channel bandwidth.For example,a TV program may be originally compressed at a high bit rate for studio applications,but later needs to be transmitted over a channel at a much lower bit rate.
In universal multimedia access[1],different terminals may have different accesses to the Internet,including local access network(LAN),digital subscriber line(DSL), cable,wireless networks,integrated services digital network (ISDN),and dial-up.The different access networks have different channel characteristics such as bandwidths,bit error rates,and packet loss rates.At the users’end,network appliances including handheld computers,personal digital assistants(PDAs),set-top boxes,and smart cellular phones are slated to replace personal computers as the dominant Manuscript received January16,2004;revised July9,2004.
J.Xin is with Mitsubishi Electric Research Laboratories,Cambridge,MA 02139USA(e-mail:jxin@https://www.doczj.com/doc/e312310785.html,).
C.-W.Lin is with the Department of Computer Science and Information Engineering,National Chung Cheng University,Chiayi612,Taiwan,R.O.C. (e-mail:cwlin@https://www.doczj.com/doc/e312310785.html,.tw).
M.-T.Sun is with the Department of Electrical Engineering,University of Washington,Seattle,W A98195USA(e-mail:sun@https://www.doczj.com/doc/e312310785.html,). Digital Object Identi?er10.1109/JPROC.2004.839620terminals for accessing the Internet.These network ter-minals vary signi?cantly in resources such as computing power and display capability.To?exibly deliver multimedia data to users with different available resources,access net-works,and interests,the multimedia content may need to be adapted dynamically according to the usage environment [2].Transcoding is one of the key technologies to ful?ll this challenging task.Transcoding is also useful for content adaptation for peer-to-peer networking over shared multihop communication links[3].
There are many other transcoding applications besides the universal multimedia access.In statistical multiplexing [4],multiple variable-bit-rate video streams are multiplexed together to achieve the statistical multiplexing gain.When the aggregated bit rate exceeds the channel bandwidth,a transcoder can be used to adapt the bit rates of the video streams to ensure that the aggregated bit rate always sat-is?es the channel bandwidth constraint.A transcoder can also be used to insert new information including company logos,watermarks,as well as error-resilience features into a compressed video stream.Transcoding techniques are also shown useful for supporting VCR trick modes,i.e., fast forward,reverse play,etc.,for on-demand video ap-plications[8]–[10].In addition,object-based transcoding techniques are discussed in[7]for adaptive video content delivery.A general utility-based framework is introduced in [11]to formulate some transcoding and adaptation issues as resource-constrained utility maximization problems.In [12],a utility-function prediction is performed using auto-matic feature extraction and regression for MPEG-4video transcoding.Several rate-distortion models for transcoding optimization are introduced in[13]to facilitate the selection of transcoding methods under a rate constraint.Envisioning the need of transcoding,the emerging MPEG-7standard[5], which standardizes a framework for describing audiovisual contents,has de?ned“transcoding hints”to facilitate the transcoding of compressed video contents[6],[7]. Dynamic change of coding parameters such as bit rates, frame rates,and spatial resolutions could also be achieved
0018-9219/$20.00?2005IEEE
Fig.1.Format conversion using a video
transcoder.
Fig.2.Block diagram of a standard video encoder.
to a limited extent by scalable coding [14],[15].How-ever,in the current scalable video coding standards,the enhancement layers are generated by coding the prediction residuals between the original video and the base-layer video.In many applications,the network bandwidth may ?uctuate wildly with time.Therefore,it may be dif ?cult to set the base-layer bit rate.If the base-layer bit rate is set low,the base-layer video quality will be relatively low and the overall video quality degradation may be severe,since the prediction becomes less effective.On the other hand,if the base-layer bit rate is set high,the base-layer video may not get through the network completely.In general,the achievable quality of scalable coding is signi ?cantly lower than that of nonscalable coding.In addition,scalable video coding demands additional complexities at both encoders and decoders.The inherent weaknesses of scalable coding have kept it from being widely deployed in practical applica-tions.Nevertheless,scalable coding is still an active research area.A new coding standard is being developed to overcome these drawbacks [16].With these problems addressed,the scalable coding schemes may be more suitable for streaming video applications when a large number of users require different levels of format adaptations,since less computation is involved.
In this paper,the input to the transcoder is a compressed video produced by a standard video encoder.Current major video coding standards —MPEG-1[17],MPEG-2[18],MPEG-4[19],H.263[20],and the emerging H.264[21]all use hybrid discrete cosine transform (DCT)and block-based motion compensation (MC)schemes.Note that H.264uses an integer transform that approximates DCT.A block dia-gram of the standard video encoders is shown in Fig.2.MC
reduces the temporal redundancy.DCT reduces the spatial redundancy and achieves energy compaction.Quantization is performed to achieve higher compression ratio.Vari-able-length coding (VLC)is applied after the quantization to reduce the remaining redundancy.A decoder is embedded in the encoder to reconstruct video frames,which are stored in the frame memory for prediction of future frames.
A straightforward realization of a transcoder to cascade a decoder and an encoder:the decoder decodes the com-pressed input video and the encoder reencodes the decoded video into the target format.It is computationally very ex-pensive.Therefore,reducing the complexity of the straight-forward decoder-encoder implementation is a major driving force behind many research activities on transcoding.
What makes transcoding different from video encoding is that the transcoding has access to many coding parameters and statistics that can be easily obtained from the input com-pressed video stream.They may be used not only to sim-plify the computation,but also to improve the video quality.The transcoding can be considered as a special two-pass en-coding:the “?rst-pass ”encoding produces the input com-pressed video stream,and the “second-pass ”encoding in the transcoder can use the information obtained from the ?rst-pass to do a better encoding.Therefore,it is possible for the transcoder to achieve better video quality than the straightfor-ward implementation,where the encoding is single pass.The challenge of the research on transcoding is then how to intel-ligently utilize the coding statistics and parameters extracted from the input to achieve the best possible video quality and the lowest possible computational complexity.
In this paper,we discuss the issues and research results re-lated to the transcoding of video streams compressed using
Fig.3.Transcoding using
requantization.
Fig.4.CPDT architecture.
the hybrid MC/DCT schemes.An overview of transcoding architectures and techniques has been given in [22],which presents many of the fundamentals in this area.This paper is intended to provide a more in-depth view of architectures and techniques,and cover such topics as quality optimiza-tion,complexity reduction techniques,and related applica-tions such as logo and watermark insertion.
The remainder of this paper is organized as follows.In Section II,we ?rst review the transcoding techniques used for the bit-rate reduction.In Section III,we discuss the transcoding techniques for spatial and temporal resolu-tion reductions.Section IV discusses the issues associated with the standards conversion.Section V addresses the transcoding quality optimization.Section VI discusses the transcoding for information insertion.Finally,Section VII concludes this paper.II.B IT -R ATE T RANSCODING
Generally,there exist three transcoding architectures for the bit-rate transcoding:open-loop transcoders [23]–[25],cascaded pixel-domain transcoders (CPDTs)[24],[26]and DCT-domain transcoders (DDTs)[27]–[29].The open-loop architectures include selective transmission [23],[24],where the high-frequency DCT coef ?cients are discarded,and re-quantization [24],[25],where the DCT coef ?cients are requantized.Fig.3shows a requantization transcoder.The open-loop transcoders are computationally ef ?cient,since they operate directly on the DCT coef ?cients.However,they suffer from the drift problem.
The drift problem is explained as follows.A video picture is predicted from its reference pictures and only the prediction errors are coded.For the decoder to work properly,the reference pictures reconstructed and stored in the decoder predictor must be same as those in the encoder predictor.The open-loop transcoders change the prediction errors and,therefore,make the reference pictures in the de-coder predictor different from those in the encoder predictor.The differences accumulate and cause the video quality to deteriorate with time until an intrapicture is reached.The error accumulation caused by the encoder/decoder predictor mismatch is called drift and it may cause severe degradation to the video quality [26],[30].It should be noted that in the following discussions,many transcoder architectures are not strictly drift free.However,the degree of the video quality degradation caused by the drift varies with architectures.In addition,the drift will be terminated by an intrapicture.In the applications where the number of coded pictures between two consecutive intrapictures is small and the quality degradation caused by the drift is acceptable,these architectures,although not drift free,can still be quite useful due to the potentially lower cost in terms of computation and required frame memory.
Fig.4illustrates the drift-free CPDT [24],a concatena-tion of a decoder and a simpli ?ed encoder.Rather than per-forming the full-scale motion estimation,as in a stand-alone video encoder,the encoder reuses the motion vectors along with other information extracted from the input video bit-stream.Thus,the motion estimation,which usually accounts for 60%–70%of the encoder computation [31],is omitted.To
Fig.5.SDDT
architecture.
Fig.6.DCT-MC.
address another major source of computational complexity,DCT,in [26],the end-of-block locations of the output video are predicted using those of the input video,and only partial DCT is performed.
The simpli ?ed DCT-domain transcoder (SDDT)is de-rived based on the assumption that DCT,IDCT,and MC are linear operations.It was ?rst derived in [27]and [28],and then further simpli ?ed in [29],as shown in Fig.5.SDDT eliminates the DCT/IDCT and reduces the number of frame buffers by half.The DCT-domain MC (DCT-MC)[32]is the major computation-intensive operation in SDDT.As shown in Fig.6,the goal is to compute the DCT coef ?cients of the target DCT
block from the coef ?cients of its four overlap-ping DCT
blocks,
–.To speed up the DCT-MC,several fast schemes have been proposed.In [33],the DCT-MC is simpli ?ed through a matrix decomposition.A fast algorithm utilizing shared information in a macroblock (MB)is pro-posed in [34].In [35],the fact that the energy of a DCT block is concentrated in its low frequency coef ?cients is exploited to perform an ef ?cient approximation of the MC operation.Another approach is to separate the MC into two one-dimensional (1-D)operations [36],which are further simpli ?ed by a lookup table scheme [37].
With these fast algorithms,SDDT may require less com-putation and memory than CPDT.However,the linearity assumptions on which the derivation is based are not strictly true,since there are clipping functions performed in the video encoder/decoder,and rounding operations performed in the interpolation for fractional-pixel MC.The failed as-sumptions may cause drift in the transcoded video.Detailed analyses of the causes and impacts of drift can be found in [30].
In addition,SDDT can only be applied to bit-rate transcoding,since it assumes that the frame memories in the encoder and the decoder have the same spatial/temporal resolution and the output video uses the same frame coding types,motion vectors and coding modes as the input video.In contrast,CPDT enjoys the ?exibility to allow changes in these coding parameters.
The cascaded DCT-domain transcoder (CDDT)[38],shown in Fig.7,can be used for spatial/temporal resolution downscaling and other coding-parameter changes.How-ever,compared to SDDT,its ?exibility is achieved using additional DCT-MC and frame memory,which results in a signi ?cantly higher cost in computation and storage.It is thus often adopted for downscaling applications,where the encoder-side DCT-MC and memory will not cost much,since the encoder operates at a reduced resolution [39],[40].Table 1compares the computational complexity of ?ve different MPEG-2transcoders:CPDT,SDDT,CDDT,CPDT using full-scale full-search motion reestimation (DEC-ENC1),and CPDT using three-step fast search motion reestimation (DEC-ENC2).Two 300-frame CIF
(352288)test sequences,“Foreman ”and “Mobile &Cal-endar,”coded with two group-of-pictures (GOP)structures,
(15,1)(i.e.,IPPP )and
GOP
(i.e.,IBBP ),are used in the simulations.The experiments are performed on a Pentium-IV 1.8-GHz PC.The two DCT-domain transcoders are signi ?cantly faster than the pixel-domain transcoders based on our implementations.It should be noted that the speed comparison might depend on the speci ?c implemen-tations of the architectures.There exist different low-level optimization methods that can be used to reduce the com-putational complexities of CPDT,SDDT,and CDDT.For example,the method in [90]can signi ?cantly speed up CPDT,while the methods in [29]and [33]–[35]can speed up SDDT and CDDT.
Our experiments show that the pixel-domain transcoders (except DEC-ENC2)usually have better peak signal-to-noise ratio (PSNR)performance as illustrated in Figs.8and 9.In Fig.8,the test video is
?rst encoded at QP Quantization
Parameter
and
GOP ,and the bit rate is then reduced using the
?ve transcoders by transcoding at
QP
,respectively.In Fig.9,the incoming video is transcoded
at
QP
for ?ve different GOP sizes
GOP ,
Fig.7.CDDT architecture.
Table 1
Runtime Complexity Comparison of Five Different Transcoders.The Video Sequences Are Encoded at QP =7,and Then Transcoded at QP =
15
for ,
and ,respectively).The number associated with each operation point indicates the bit rate generated.We can observe from Figs.8and 9that the drift caused by the two DCT-domain transcoders is not serious for small GOP sizes.However,the performance degradation,especially for SDDT,can become rather signi ?cant with large GOP sizes.Such large GOP sizes may be used in applications such as networked video streaming and wireless video that demand high coding ef ?ciency.III.S PATIAL AND T EMPORAL T RANSCODING
The heterogeneity of communication networks and network access terminals often demand the conversion of compressed video not only in the bit rates,but also in the spatial/temporal resolutions.One of the challenging tasks in spatial/temporal transcoding is how to ef ?ciently reestimate (or map)the target motion vectors from the input motion vectors.
Many works on the motion reestimation for spatial transcoding consider the simple case of 2:1downscaling.Fig.10illustrates a case of the motion-mapping problem,where the input MBs have four motion vectors while the target output MB has a single motion vector.Several strate-gies have been proposed to compose the target motion vector using the input motion vectors.One strategy is to randomly choose from the four input motion vectors [41],[42].The weighted average taking into account the prediction error is presented in [43].Different methods are compared in [31]and [41],including median,majority,average,and random selection.The median method is shown to achieve the best performance.The work in [44]selects the motion vector using a likelihood score based on the statistical char-acteristics of the MBs associated with the best matching
motion vectors.Note that the motion vectors formed by the above algorithms need to be downscaled to the target spatial resolution.
Recent works extend these strategies to tackle the transcoding of arbitrary down-sampling ratio [45],[46]by taking care of the unequal contributions of related input mo-tion vectors.When the down-sampling ratio is large and one target MB is down-sampled from a number of input MBs,the motion vectors of the input MBs are more likely to be inconsistent.A multicandidate approach is proposed in [47]to address this issue.The transcoding of interlaced video is discussed in details in [46],where the motion mapping is further complicated by various types of frame and ?eld motion vectors.
For transcoding with temporal resolution changes,due to the frame dropping,one has to derive a new set of motion vectors that do not exist in the input video.This issue is ad-dressed in [48],where a technique called forward dominant vector selection (FDVS)is proposed.The FDVS scheme is illustrated in Fig.11.The best-match area referenced by the motion vector of the current MB overlaps with at most four MBs in its reference frame.The motion vector of the MB with the largest overlapping portion is called the dominant motion vector and is selected for composing the target motion vector.This process is repeated for all the dropped frames and the ?nal target motion vector is formed by adding all the dominant motion vectors together,followed by a motion vector re ?nement.In [49],the dominant motion vector is selected based on the activity of the overlapping MBs,instead of the area as in FDVS.Another method,telescopic vector composition (TVC)[31],accumulates all motion vectors of the current MB ’s colocated MBs in the dropped frames and adds the resulting motion vector to the current MB ’s motion vector.For typical videos with small motion vectors,TVC can achieve similar performance as FDVS.It is shown [31]that
a 2-pixel re ?nement around the composed motion vector can achieve similar perfor-mance as the full-scale full-search motion reestimation.For the spatial resolution reduction,typically a half-pixel re ?ne-ment is enough to achieve a good quality [31],[46].For the temporal resolution reduction,as the number of skipped frames increases,more re ?nement may be desirable.The re ?nement range may be dynamically decided based on the motion vector magnitudes and the number of skipped frames [50].In [48],the re ?nement range is determined based
Fig.8.Performance comparison of average PSNR for ?ve transcoders.The “Foreman ”sequence is encoded at QP =7,and then transcoded at different QP ’s,respectively.GOP =(15;1)
.
Fig.9.Performance comparison of average PSNR for CPDT,SDDT,and CDDT for different GOP sizes.The “Mobile &Calendar ”sequence is encoded at QP =5using size different GOP sizes,and then transcoded at QP =11
.
Fig.10.In 2:1spatial transcoding,the target motion vector(s)for that MB is highly correlated with the four input motion vectors.
on the input/output quantization scales and the prediction errors.In [51],a fast motion vector re ?nement scheme is
proposed for the DCT-domain spatial downscaling,where the speedup is achieved through exploiting the redundancies in the DCT-MC computations of two adjacent checkpoints.Due to the spatial/temporal resolution reduction,the drift problem is usually signi ?cant in open-loop transcoding architectures [52].Therefore,the drift-free CPDT architec-ture is more favorable in terms of quality.In [53]and [54],the drift in spatial transcoding is analyzed.Based on the analyses,several drift-compensation architectures providing different levels of complexity-quality tradeoffs are proposed.In-depth analyses and performance comparisons of these alternative architectures and CPDT are provided in [55].A DCT-domain architecture is proposed in [56]for tem-poral transcoding,where the reencoding errors are reduced using the direct addition of DCT coef ?cients and signals
Fig.11.FDVS.V and V are dominant motion
vectors.
Fig.12.Example of MPEG-2to MPEG-4simple pro ?le transcoding.
from an error compensation feedback loop.In [57],a hybrid DCT/pixel-domain transcoder architecture is proposed for video downscaling.It contains a DCT-domain decoder fol-lowed by a pixel-domain encoder,where a modi ?ed DCT-do-main inverse transformation and down-sampling method is developed to convert a DCT block into a downscaled pixel block.
IV .S TANDARDS T RANSCODING
In many applications,video coded in one coding standard (e.g.,MPEG-2)may need to be converted to another standard (e.g.,MPEG-4)besides the changes in bit rate and resolution.In what follows,we use two examples to illustrate how the information obtained from the input video sequence may be used to help the standards transcoding process.
A.MPEG-2to MPEG-4Simple Pro?le (SP)Transcoding MPEG-4SP is aimed at low-complexity and low-bit-rate video https://www.doczj.com/doc/e312310785.html,pared to MPEG-2video,it does not support B-frames and interlaced video.In addition,it usually operates at lower spatial resolutions and frame rates than MPEG-2video.Fig.12illustrates a typical scenario:an interlaced MPEG-2video of
720480resolution and at 30frames/s is transcoded to the progressive MPEG-4SP of
176144resolution at 15frames/s.It involves conversion of video formats and frame coding types besides the spatial and temporal resolution conversions.The new challenge is that the motion vectors of an incoming video frame may not use the same reference frame as the target frame.
The motion reestimation problem in the case of frame type conversion is ?rst discussed in [31],where the target mo-tion vector is chosen from several candidate motion vectors
that are formed by using the motion information from cur-rent and adjacent frames.The work in [58]and [59]intro-duces an intermediate,virtual layer of video,which has the same frame rate and frame type as the target video and the same spatial resolution as the input video.The motion rees-timation process consists of two steps.In the ?rst step,one or more intermediate motion vectors are formed for each MB in the intermediate video frame using the motion information of the input video.In the second step,these motion vectors of the intermediate-layer video are used to compose the mo-tion vectors for the target video.This step also takes care of the mismatch of the motion vector types caused by the inter-laced input and the progressive output.Effectively,the ?rst step handles the frame-rate reduction and the frame-type con-version,and the second step deals with the spatial-resolution reduction and the interlaced-to-progressive processing.This two-step process has low complexity,since all operations are performed on the motion vectors and,therefore,the compu-tationally expensive block matching is not needed.B.MPEG-2to MPEG-4Advanced Simple Pro?le (ASP)Transcoding
Aiming at providing high quality video coding,MPEG-4ASP incorporates several new coding tools.One of the tools is global MC (GMC),which can improve the coding per-formance for scenes with global motions [60].No previous video coding standards,including MPEG-2,support GMC.Therefore,in the transcoding of MPEG-2to MPEG-4ASP,global motion (GM)parameters may be estimated to take ad-vantage of this tool.The estimation is referred to as global motion estimation (GME).Direct GME methods operate in the pixel-domain [61],[62].They are computationally ex-pensive due to the iterative processes in the nonlinear esti-
mations and the number of pixels involved when the general perspective model is used.
A much more ef?cient algorithm is presented in[63]by performing the GME based on the input M
B motion vec-tors,instead of on estimating the pixel-wise motion vector for each decoded pixel.The motion vectors in the input video stream are obtained from the block matching motion estima-tion process.They contain GM information plus local mo-tion and noise due to the inaccurate block-matching process. The local motion and the block-matching noise are modeled as a Gaussian distribution with zero mean.The GM param-eters are obtained by iteratively minimizing the?tting error between the input motion vectors and the sampled motion vectors generated from the estimated motion model using the Newton–Raphson method with outlier rejections.This com-pressed-domain GME is shown to be fast(only requires less than0.2%of the processing compared to the pixel-domain GME implemented in the MPEG-4reference software),ro-bust,and give accurate results,so the computationally expen-sive pixel-domain GME can be saved.
C.Transcoding Between Other Standards
The recently developed scalable coding standard MPEG-4?ne granularity scalability(FGS)[15]has attracted interests of transcoding between FGS and single-layer video.An ef?-cient architecture is derived in[64]for transcoding the FGS video to a single-layer video.In[65],it is pointed out that at the same bit rate,the transcoding from FGS to single-layer yields better video quality than simply truncating the FGS bit-stream.Various methods for transcoding a single-layer MPEG stream to an FGS stream,both with the open-loop and closed-loop structures,are investigated in[66].
The syntax translation between different formats with minimal quality loss is addressed in[67],where mapping techniques of the syntactic and semantic elements of H.263 and MPEG-4video are presented.Other format transcoding techniques not covered by this section can be found in [68]–[70].
V.T RANSCODING Q UALITY O PTIMIZATION
As mentioned earlier,transcoding can be considered as the second pass of a two-pass video encoding process where the input video bit-stream is considered as the result of the ?rst pass.Many useful statistics,such as the quantization step sizes,coding modes,coded bits of each MB and frame, and motion vectors,can be easily obtained from the input video bit-stream to help the second pass encoding.There-fore,it is possible for the transcoder to achieve better video quality than the direct one-pass encoding using the original source.Although,in the transcoding,the video is encoded twice,the degradation in the?rst encoding pass may be neg-ligible compared to the degradation in the second encoding pass.In what follows,we discuss the technologies related to the video quality optimization:requantization,rate control, and mode decision.A.Requantization
Quantization is the only operation in current video coding standards that introduces quality loss.Video coding stan-dards specify the representation levels of the quantization, not the decision levels.Not considering other constraints,the optimal quantizer simply maps an input value to its nearest representation level[71].In[72],optimal requantization for transcoding MPEG-2intraframes(I-frames)in the proba-bilistic sense are proposed based on two principles:mini-mization of the MSE(MMSE)cost function and maximum a posteriori(MAP).Both methods require the knowledge of the original quantization method and the original DCT coef?cients distribution,which may be carried in the input video stream as the user data or may be estimated from the input video with minor additional complexity.Methods for estimating model parameters for this purpose are discussed in[73].The MMSE and MAP requantization strategies are shown to achieve improved performance compared to those designed for a video encoder.The requantization distortion is especially signi?cant for certain ratios between output and input quantization scales[72],[74].This leads to the selec-tive requantization scheme[74]that simply avoids those crit-ical input/output quantization-scale ratios in the decision of quantization scales.In[75],the quantization is optimized jointly with deblocking.
B.Rate Control
Rate control determines quantization parameters and is responsible for maintaining consistent video quality while satisfying bandwidth,delay,and memory constraints.Gener-ally,all rate-control algorithms designed for video coding are applicable to transcoding,for instance,MPEG-2TM5[76]. In practice,however,functional limitations need to be con-sidered.For example,a rate-control algorithm usually needs to know the GOP con?guration.However,in transcoding,the output GOP con?guration is often determined by the input one,since transcoding typically does not change the frame coding types in order to keep complexity low.In real-time transcoding,the input GOP con?guration is usually unknown to the transcoder.For these applications,in order to use the GOP-based rate-control algorithms,the input GOP con?gu-ration needs to be estimated.One solution is to predict the current GOP con?guration based on the con?guration of the immediately preceding GOP and adjust the rate-control algo-rithm accordingly when new GOP parameters are detected [77].Another solution is to simply scale the bits of each frame according to the rate conversion ratio[78].In[79], in addition to scaling the input frame bit number,relatively more bits are allocated to I-frames,since I-frames need a larger portion of the available bit budget to achieve a con-sistent quality with other frames[46],[59],[79],especially when the target bit rate is low.
For applications where the delay of a GOP time is allowed such that the coding statistics of the current input GOP can be collected before transcoding,improved rate control can be achieved by making use of the coding statistics[46].A rate-control algorithm allocates bits to frames proportional to
Fig.13.Performance of the bit-allocation using output or input complexity(X).
their complexities.In video coding,however,the current and future frame complexities are usually unknown prior to en-coding.Rate-control algorithms designed for encoding,such as MPEG-2TM5,based on the stationary assumption,es-timate the complexity of the current frame using the com-plexity of the previous frame of the same type.It is well known that this estimation is poor when the stationary as-sumption fails.In transcoding,intuitively it is possible to compute the frame complexities from the input bit-stream (since the quantization step sizes and the number of bits in-formation are available),and then use these complexities for the bit allocation in transcoding.The approach of scaling down the input frame bits is one special case of such algo-rithms where the number of bits is taken as the complexity measure.It is found in[46]and[80]that complexity mea-sures depend on the coding bit rate.Therefore,the com-plexity measures calculated from the input video bit-stream at the input bit rate may not be suitable to directly serve as the complexity measure for coding the frames at the output bit rate.Instead,the correlations between the complexity mea-sures of the input and output videos are utilized to provide a more accurate estimation of the output frame complexity, which leads to improved bit-allocation and video quality as shown in Fig.13,where the transcoder input and output are both MPEG-2,the bit rate is reduced from10to4Mb/s.The above techniques can be adapted to the joint transcoding of multiple preencoded video streams(statistical multiplexing) [4],[81],[82].
MB-layer rate control adjusts the quantization parameters based on the encoder buffer feedback and is particularly de-sirable for low-delay transcoding.Research works on this topic can be found in[59],[79],and[83].In[7],a joint rate-control scheme taking into account the various spatio-temporal tradeoffs among all objects in a scene for MPEG-4 object-based transcoding is proposed.Dynamic rate-control algorithms tailored for multipoint video conferencing are dis-cussed in[84]–[86].
C.Mode Decision
There are various levels of mode decisions,including MB-level,frame-level,and object-level.Rate-distortion optimized mode decision techniques are explained in details in[87].These techniques are also applicable to transcoding. However,suboptimal but simple mode decision strategies are often desirable in complexity-constrained transcoding. In bit-rate transcoding,typically the modes of the input video are reused by the transcoder[28].
Fig.14.Logo insertion in:(a)the pixel domain and(b)the DCT domain. In spatial transcoding,the MB-type(inter/intra)deci-sion usually follows the majority of the input MB-types [31],[46].Various heuristic strategies are discussed in[54] to perform the decision for the open-loop architectures. MB prediction-mode decision techniques,including the frame/?eld prediction for interlaced transcoding,are dis-cussed in[46].A good overview of MB-level mode decision techniques can be found in[22].
Dynamic frame skipping based on the accumulated mag-nitude of motion vectors is proposed in[50]and[86].In[7], strategies are proposed to drop less relevant objects if the scene has been coded as a set of objects.In[6],it is demon-strated that transcoding hints of MPEG-7are valuable in im-proving mode decisions at various levels.
VI.I NFORMATION I NSERTION T RANSCODING
In general,any operation that changes the content of a compressed video stream may be regarded as transcoding.In this section,we discuss two information insertion examples.
A.Logo/Watermark Insertion
For copyright protection,video watermarks and company logos can be inserted into the compressed video stream[88]. In the pixel-domain transcoders,the logo insertion can be implemented as illustrated in Fig.
14(a)
where,
and are the pixel values of the logo
signal,the decoded picture,and the logo-inserted picture
for
frame,
respectively.
and are the scaling factors
for
frame controlling the intensity of the logo in order to
provide uniform visibility[89],[90].Ef?cient architectures
performing this operation in the compressed-domain as
illustrated in Fig.14(b)are proposed in[88]and[90].These
architectures realize the same function as their pixel-domain
counterpart does.
Fig.15shows a logo and a sample picture after logo in-
sertion in the DCT domain[90].The logo is inserted into an
MPEG-2encoded bit-stream whose bit rate is reduced from
8to4Mb/s.The approach of[89]inserts the information in a
simple,open-looped manner,where only the area affected by
the inserted information needs to be modi?ed.However,it is
subject to drift.The insertion of new information may affect
the optimality of the existing coding parameters of the af-
fected picture area,including the motion vectors and coding
modes as discussed in[91],where techniques are discussed
to modify these coding parameters.
B.Error-Resilience Transcoding
In practical applications where video contents are com-
pressed and stored for future delivery,the encoding process
is typically performed without enough prior knowledge
about the channel characteristics of network hops between
the encoder and the decoder.In addition,the heterogeneity
Fig.15.DCT-domain logo insertion (
=0:2; =0:8).(a)Logo.(b)Logo-inserted sample
picture.
Fig.16.System framework of error-resilience video transcoder.
of client networks also makes the encoder dif ?cult to adapt the video contents to a wide degree of different channel conditions,especially for wireless client terminals.To over-come these problems,a video transcoder can be placed in a network node (e.g.,mobile switch/base-station,proxy server,and video gateway)connected to a high-loss network (e.g.,wireless network or highly congested network)to insert error-resilience features into the video bit-stream to achieve robust video transmission over wireless channels.Fig.16shows a typical example of error-resilience transcoder with feedback [92]–[94].The transcoder ?rst extracts the video features (e.g.,locations of video data which are likely to result in more serious error propagation if lost)from the incoming bit-stream as well as estimates the client channel conditions according to the feedback channel statistics.The extracted features and the estimated channel conditions are then used to determine the error resilience policy that guides the joint allocation of source/channel coding resources.The features of video contents can also be precomputed in the front-end encoding process and sent to the transcoder as auxiliary data to assist the https://www.doczj.com/doc/e312310785.html,monly used error-resilience source coding tools [95]include data partitioning,synchronization marker,reversible variable length codes (RVLC),error-resilience entropy coding (EREC),multiple-description coding (MDC),refer-ence frame selection (RFS),adaptive intra refresh (AIR),
and so on.Forward error correction (FEC)and automatic retransmission request (ARQ)are two major schemes for channel protection.
An error-resilience MPEG-2transcoding scheme based on EREC is proposed in [96].In this method,the incoming bit-stream is reordered without adding redundancy such that longer VLC blocks ?ll up the spaces left by shorter blocks in a number of VLC blocks that form a ?xed-length EREC frame.Such ?xed-length EREC frames of VLC codes are then used as synchronization units,where only one EREC frame,rather than all the codes between two synchronization markers,will be dropped should any VLC code in the EREC frame be corrupted due to transmission errors.In [92],the authors propose a rate-distortion frame-work with analytical models that characterize the error propagation of a corrupted video bit-stream subjected to bit errors.These models are then used to guide the use of spatial and temporal localization tools:synchronization markers and intrarefresh,respectively,to compute the op-timal bit-allocation among spatial error-resilience,temporal error-resilience,and the source rate.The work in [93]proposes an error-resilience transcoder for general packet radio service (GPRS)mobile-access networks with the transcoding process performed at a video proxy that can be located at the edge of two or more networks.Two error-re-silience tools:the AIR and RFS methods with feedback control signaling (FCS)are used adaptively to reduce error effects,while preserving the transmission rate adaptation feature of the video transcoders.In [97],a rate-distortion optimized GOP-based bit-allocation scheme is proposed based on models accounting for the interframe dependence in both video source requantization and error propagation of motion compensated video.In [94],the authors propose a multiple-description FEC (MD-FEC)-based transcoding
scheme,which uses
the
Reed –Solomon erasure-correction block code to protect the th layer of
an -layer scalable video.The multiple-description packeti-zation method is specially designed to allow the th layer to be decodable when or more descriptions arrive at the decoder.The scheme in [98]proposes to implement an ARQ proxy at the base station of a wireless communication system for handling ARQ requests and tracking errors to reduce retransmission delays as well as to enhance the error resilience.The ARQ proxy resends important lost packets (e.g.,packets with header information and motion vectors)detected through the retransmission requests from wireless client terminals,while dropping less important packets (e.g.,packets carrying DCT coef ?cients)to meet the bandwidth limit.A transcoder is used to compensate for the mismatch error between the front-end video encoder and the client decoders caused by the dropped packets.VII.C ONCLUSION
In this paper,we provide an overview of issues related to transcoding,including transcoding applications,transcoder architectures,techniques for reducing the computation,and techniques for improving the video quality.Transcoding is an active research topic.The challenge is how to use the
information from the input video bit-stream to reduce the complexity of a transcoder and improve the quality of the output video.Video transcoding is also related to the re-search activities on compressed-domain video processing, since the incoming video stream to a transcoder is in the compressed-domain.As new video coding standards con-tinue to be developed,the need for transcoding will continue to exist.For example,currently,MPEG-2video is widely used in digital TV,DVD,and HDTV applications.However, newer coding standards such as H.264/MPEG-4A VC have been developed which perform much better than MPEG-2.A transcoder will be useful for solving format incompatibility problems for universal multimedia access.
A CKNOWLEDGMENT
The authors would like to thank Dr. A.Vetro and Prof.S.-F.Chang for their valuable suggestions to improve this manuscript.
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域名解析详细教程 域名解析是把域名指向网站空间IP，让人们通过注册的域名可以方便地访问到网站一种服务。域名解析也叫域名指向、服务器设置、域名配置以及反向IP登记等等。说得简单点就是将好记的域名解析成IP，服务由DNS服务器完成，是把域名解析到一个IP地址，然后在此IP地址的主机上将一个子目录与域名绑定。 英文名：DNSR(domain name system resolution) 在域名注册商那里注册了域名之后如何才能看到自己的网站内容，用一个专业术语就叫“域名解析”。在相关术语解释中已经介绍，域名和网址并不是一回事，域名注册好之后，只说明你对这个域名拥有了使用权，如果不进行域名解析，那么这个域名就不能发挥它的作用，经过解析的域名可以用来作为电子邮箱的后缀，也可以用来作为网址访问自己的网站，因此域名投入使用的必备环节是“域名解析”。 域名解析(17张) 我们知道域名是为了方便记忆而专门建立的一套地址转换系统，要访问一台互联网上的服务器，最终还必须通过IP地址来实现，域名解析就是将域名重新转换为IP 地址的过程。一个域名对应一个IP地址，一个IP地址可以对应多个域名；所以多个域名可以同时被解析到一个IP地址。域名解析需要由专门的域名解析服务器(DNS)来完成。解析过程，比如，一个域名为：***.com，是想看到这个现HTTP服务，如果要访问网站，就要进行解析，首先在域名注册商那里通过专门的DNS服务器解析到一个WEB服务器的一个固定IP上：211.214.1.***，然后，通过WEB服务器来接收这个域名，把***.com这个域名映射到这台服务器上。那么，输入***.com这个域名就可以实现访问网站内容了.即实现了域名解析的全过程；人们习惯记忆域名，但机器间互相只认IP地址，域名与IP地址之间是对应的，它们之间的转换工作称为域名解析，域名解析需要由专门的域名解析服务器来完成，整个过程是自动进行的。域名解析协议（DNS）用来把便于人们记忆的主机域名和电子邮件地址映射为计算机易于识别的IP地址。DNS是一种c/s的结构，客户机就是用户用于查找一个名字对应的地址，而服务器通常用于为别人提供查询服务。
设置域名解析？（www和泛解析） 登陆ID后，可以通过“管理中心——用户菜单——域名管理——域名管理——（请输入条件查询信息）——列出所有域名——（找到对应域名）——[管理]——解析管理”进入“域名控制面板”操作设置。 1）登录ID，进入管理中心“用户菜单——域名管理”。 2）在输入条件查询信息中输入关键字，通过“域名类型”“注册模版”“域名分类”“域名状态”等多种方式或选择其中一种后，点击“查询”来查找域名。（注：可以直接点击“查询”列出所有域名）
3）查找到需要解析的域名后，点击域名后的[管理]按钮，即可进行相应操作。 4）在域名管理页面中选择“解析管理”进入域名解析操作界面。
5）按照图示进行设定之后，点击新增一条，即可完成域名解析。 例如域名：https://www.doczj.com/doc/e312310785.html,，主机名设置*（泛解析），类型A，IP地址即为您主机的IP，设置后即可以任何前缀+域名进行访问，如 https://www.doczj.com/doc/e312310785.html,或https://www.doczj.com/doc/e312310785.html,等等；主机名为空（没有填写任何字符），类型A，IP地址即为您主机的IP，设置后是以域名直接访问；如 https://www.doczj.com/doc/e312310785.html, 主机名为www，类型A，IP地址即为您主机的IP，设置后是以www+域名进行访问，如https://www.doczj.com/doc/e312310785.html,。
如何设置别名记录(CNAME)？ 登录ID后，可以通过“管理中心——用户菜单——域名管理——域名管理——（请输入条件查询信息）——列出所有域名——（找到对应域名）——[管理]——解析管理”进入“域名控制面板”操作设置别名记录。 1）登录ID，进入管理中心“用户菜单——域名管理”。
2）在输入条件查询信息中输入关键字，通过“域名类型”“注册模版”“域名分类”“域名状态”等多种方式或选择其中一种后，点击“查询”来查找域名。（注：可以直接点击“查询”列出所有域名） 3）查找到需要设置别名记录的域名后，点击域名后的[管理]按钮，即可进入域名管理页面。
第16章第1节动物运动方式的多样性同步练习 一、选择题 1.下列有关动物运动的说法正确的是（） A.动物运动方式的多样性是对不同生活环境的适应，虽然它们的运动器官不同，但它们的共同特点是：具有适应不同环境的特化的运动器官。 B.鸟类在不同的季节里都有迁徙行为。 C.能在空中飞行的动物只有鸟类和昆虫。 D.海蛇、草履虫、野鸭、河蚌的运动方式均是游泳。 2.世界上最大的鸟――鸵鸟的运动方式主要是（） A.飞行 B.爬行 C.游泳 D.行走 3.选出运动方式相同的一组动物（） A.河蟹、野鸭 B.袋鼠、鸵鸟 C.企鹅、麻雀 D.鳄鱼、蜥蜴 4.下列动物的运动方式主要为飞行的是： A 、鸵鸟 B、企鹅 C、蝙蝠 D、蚕蛹 5.动物通过运动提高了适应环境的能力，蜥蜴的主要运动方式为： A 、飞行 B、跳跃 C、爬行 D、奔跑 6.下列哪项不是鸟类迁徙的意义： A、获取足够的食物 B、寻找适宜的生活环境 C、产生有利变异 D、有利完成生殖活动 7.变形虫的运动依靠：
A、纤毛 B、鞭毛 C、伪足 D、伸缩泡 8.生活在亚洲丛林中的鼹鼠在伸展四肢的时候，可以看到其身体两侧皮肤的飞膜，由此可推测鼹鼠的运动方式是： A、滑翔 B、奔跑 C、爬行 D、飞翔 二、非选择题 1.阅读下面短文，回答问题： 一只可爱的小兔子在长满青草和开有小花的山坡上，一边沐浴着灿烂的阳光，一边品尝着清香可口的小草。它不时地移动着身体，走到最嫩的小草旁。突然，可爱的小精灵发现天空中一只老鹰迅速向下飞来，它飞快地向坡那边的林子里跑去。小白兔拼命地奔跑着，越过小沟，老鹰迅速地飞着、追着。小白兔终于躲进了林子，老鹰灰溜溜地飞走了。敌情解除后，小白兔发现林子那边的草长得更茂盛，花开的更艳丽，又自由地在这边草地上快活地舞蹈着。 （1）说出上面短文中描述了动物哪些运动方式_______________________________。 （2）试说出小白兔具有的运动本领对它有哪些意义。__________________________ ________________________________________________。 2.动物的运动因种类而不同，根据常见的类别填写下表：（填写对应序号）
动物的活动方式教案 【篇一：科学活动：动物的活动方式】 领域活动计划 科学活动：动物的活动方式（动植物） 一、活动目标： 1、发现动物的活动方式是多种多样的。 2、尝试用肢体动作模仿动作的活动方式。 二、活动准备： 经验准备：请家长带幼儿到动物园观察动物。 教材配套：教育挂图《领域活动—科学— 动物的活动方式》，操作材料：《送动物回家》，亲子手册：《领 域活动—谁会跑？》。 三、活动过程： 1、引导幼儿观察挂图，说说挂图上有哪些动物。 引导幼儿观察挂图上动物的活动方式，说说：挂图上的动物都有哪 些活动方式？哪些动物是用脚行走的？哪些动物主要是在天空飞行的？哪些动物是在水里游的？ 2、说说动物都有哪些活动方式。 引导幼儿说说动物都有哪些活动方式？。 教师结合挂图，小结：小鸟有两只脚，能在地上行走，但主要是在 天上飞。河里的小鱼只能在水里游；而鳄鱼也有脚，既可以在水里游，也能在陆地上行走。猴子、老虎、小兔、斑马都是靠脚来行走的。蛇是靠身上的鳞片和地面摩擦来行走的。动物们的活动方式多 种多样。 3、送小动物回家。 引导幼儿完成操作材料《送动物回家》，按照动物的活动方式将贴 纸贴在合适的位置。 4、模仿游戏。 引导幼儿玩模仿动物活动的游戏。 玩法：有而模仿动物活动，边做动作边说：我是xxx，我会飞（跑、走、游、跳）。 5、引导幼儿放松，活动结束。 活动反思：
透过一个故事，遇到危险的长颈鹿，将孩子带进这个活动，长颈鹿在遇到危 险的时候，生活在不同地方的动物纷纷给出意见，以此来了解动物们分别生活的地方并有什么不同。孩子们兴趣很浓厚，特别是故事也很有吸引力。除了个别孩子讲话，大家都积极参与活动，有的积极发言。 【篇二：《动物运动的方式》教学设计(2)】 第一节动物的运动方式 教学过程 【篇三：《动物运动的方式》教学设计(1)】 动物的运动方式 ●教学目标 知识目标 1．列举生物多样性三个层次，概述它们之间的关系。 2．认识我国生物多样性的现状及其独特性。 3．说明保护多样性的重要意义。 能力目标 1．通过对课本资料分析，培养学生思考分析、归纳总结能力，学会收集和整理信息的方法。 2．培养学生在已有知识和生活经验的基础上获取新知识的能力、综合运用知识能力。 情感目标 1．通过本章学习，主要在同学心目中建立起生物（包括人）与环境相适应的辩证观点。 2．激发同学们保护生物栖息环境、保护生态系统的多样性的热情、渗透爱国主义教育。 ●教学重点 1．生物多样性的三个方面内容及它们之间的关系。 2．基因多样性。 3．说明保护多样性的意义。 4．培养学生收集和整理信息的能力。 ●教学难点 1．生物多样性的三个方面内容以及它们之间的关系。 2．基因多样性。
初二生物动物运动方式的多样性教案 第16章第1节动物运动方式的多样性 知识与能力目标： 举例说出动物运动方式的多样性;举例说明动物运动的重要性。 过程与方法目标： 通过调查、观察等，收集有关动物运动的资料，培养学生应用资料分析问题、解决问题的能力;通过观察、讨论、交流等进一步培养学生自主学习、合作学习、探究学习的能力。情感态度与价值观目标： 通过合作讨论，培养爱护大自然的情感，建立起生物(包括人)与环境相适应的辩证观点。激发同学们保护生物栖息环境、保护生态系统的多样性的热情。 教学重点： 举例说出动物运动方式的多样性;举例说明动物运动的重要性。 教学难点： 举例说明动物运动的重要性。 课前准备： 学生准备： ①调查和观察生活在水中、空中、地面下、地面上动物的运动方式并记录在表格中以及收集动物运动方式与生活环境
的关系的有关资料。 主要活动区域动物运动方式 天空 陆地 水中 ②收集有关动物运动的图片和画册。 ③准备各种典型的易于捕捉的较小型的动物。 教师准备： 制作多媒体课件;准备观察实验的用的小动物。 教学进程 课堂流程教师活动学生活动 情境导入 多媒体展示视频 去年东南亚发生海啸时，在泰国的普吉岛，有头大象驮着许多的孩子快速奔跑逃离了危险的海滩。那么动物的运动对动物有什么意义呢? 人们常说：海阔凭鱼跃，天高任鸟飞。不同的动物有着不同的运动方式。鹰击长空、鱼翔浅坻、麋鹿奔跑、企鹅游弋等等构成了大自然动态的美丽画卷。 下面我们先来欣赏一段大自然中动物运动的片段。 自然界中各种动物的运动 通过刚才的欣赏你看到了什么?有什么感受? 激起学生的好
奇心和求知欲，激发学习的主动性，提高学习兴趣 感受自然界中动物运动方式的多样性。说出动物在运动并感受大自然的美。
动物运动方式的多样性 课题 : 《动物运动方式的多样性》学案时间: 2019年10月20日 主备: 张成班级：八年级（）班学生____________ 【学习目标】 1、举例说出动物运动方式的多样性。 2、举例说明动物运动的重要性。 【自学导航】 自主学习：阅读课文50-51页，完成以下练习。 1、自然环境 2、动物的运动方式多种多样，主要有 3、动物在长期的进化过程中，逐渐形成一系列通过运动能力。 4、动物通过运动能迅速迁移到更为适宜的和，从而有利于自身的和。 【合作探究】 小组展开讨论，交流展示 E.飞行或滑翔 F.旋转式运动 G.翻筋斗运动 H.奔跑探究二：举例说动物运动的重要 性 动物通过运动主动的适应______________ 1. ___________________________________________________________________ 如:___________________________________________________________________ 2. ____________________________________________________________________ 如：__________________________________________________________________ 【分层检测】 一、应知应会 1、下列动物的运动方式主要为飞行的是： A 、鸵鸟 B、企鹅 C、蝙蝠 D、蚕蛹
2、动物通过运动提高了适应环境的能力，蜥蜴的主要运动方式为： A 、飞行 B、跳跃 C、爬行 D、奔跑 3、下列哪项不是鸟类迁徙的意义： A、获取足够的食物 B、寻找适宜的生活环境 C、产生有利变异 D、有利完成生殖活动 二、达标测评 1.世界上最大的鸟――鸵鸟的运动方式主要是------------------------------------------------------------------（） A.飞行 B.爬行 C.游泳 D.行走 2.选出运动方式相同的一组动物-------------------------------------------------------------------------------------（） A.河蟹、野鸭 B.袋鼠、鸵鸟 C.企鹅、麻雀 D.鳄鱼、蜥蜴 3.下列动物的运动方式主要为飞行的是：------------------------------------------------（） A 、鸵鸟 B、企鹅 C、蝙蝠 D、蚕蛹 4.动物通过运动提高了适应环境的能力，蜥蜴的主要运动方式为：--------------------------（） A 、飞行 B、跳跃 C、爬行 D、奔跑 6.下列哪项不是鸟类迁徙的意义：------------------------------------------------------（） A、获取足够的食物 B、寻找适宜的生活环境 C、产生有利变异 D、有利完成生殖活动 7.生活在亚洲丛林中的鼹鼠在伸展四肢的时候，可以看到其身体两侧皮肤的飞膜，由此可推测鼹鼠的运动方式是：------------------------------------------------------------------------------（） A、滑翔 B、奔跑 C、爬行 D、飞翔 三、拓展提升 一些鸟类通过迁徙来度过严寒的冬天，而其他动物是怎样度过冬天的？
动物运动方式的多样性 知识与能力目标： 举例说出动物运动方式的多样性；举例说明动物运动的重要性。 过程与方法目标： 通过调查、观察等，收集有关动物运动的资料，培养学生应用资料分析问题、解决问题的能力；通过观察、讨论、交流等进一步培养学生自主学习、合作学习、探究学习的能力。情感态度与价值观目标： 通过合作讨论，培养爱护大自然的情感，建立起生物（包括人）与环境相适应的辩证观点。激发同学们保护生物栖息环境、保护生态系统的多样性的热情。 教学重点： 举例说出动物运动方式的多样性；举例说明动物运动的重要性。 教学难点： 举例说明动物运动的重要性。 课前准备： 学生准备： ①调查和观察生活在水中、空中、地面下、地面上动物的运动方式并记录在表格中以及收集动物运动方式与生活环境的关系的有关资料。 主要活动区域动物运动方式 天空 陆地 水中 ②收集有关动物运动的图片和画册。 ③准备各种典型的易于捕捉的较小型的动物。 教师准备： 制作多媒体课件；准备观察实验的用的小动物。 教学进程 课堂流程教师活动学生活动
动物运动方式的多样性 相互交流，探讨体验 多媒体展示图表 描述动物的运动 观察实验小结 大自然真是多姿多彩，令人赏心悦目。草 木荣枯，候鸟去来，蚂蚁搬家，蜻蜓低飞。动 物的运动是大自然最丰富也是最有韵律的动 态语言。 课前请同学们观察和调查了各种动物的 运动并将各种动物及运动方式按照活动区域 填入表格中，另外还请同学们收集动物运动的 图片。下面请同学们四人一组进行交流，①举 例说出各种动物的运动方式，并关注它们生活 的环境。②说出图片中各种动物的运动方式。 动物的运动方式多种多样，由于生活环境 的不同运动方式也不同。经过交流，引导学 生举例说出动物的运动方式有哪些？ 主要活动区域运动方式 空中 陆地 水中 动物的运动让我们感受到了大自然无穷 的魅力。下面我请几个同学描述几种动物的 运动。 自然界中的各种动物的运动都有着自己 的韵律和美感。现在我们亲自观察几种动物 的运动。注意观察动物的运动方式？如何完成 运动的？ 引导学生形象描述几种动物的运动方式 及如何完成运动的。 不同生活环境中的动物运动方式也不同， 课前观察各种动物的运动方式 并记录，将记录的信息交流， 说出图片中各种动物的运动方 式。 按照活动区域，说出动物的运 动方式：空中的有飞行、滑翔； 陆地上的有爬行、奔跑、跳跃、 攀缘、行走等；水中的有游泳、 漂浮等。 用图片和文字描述几种动物的 运动 将各种典型的易于捕捉的较小 型的动物带到学校进行观察探 究。各小组观察小螃蟹和小虾 子的运动。 学生描述动物的运动 描述所观察的现象。
域名绑定和域名解析详解 如何获得IP地址？ 微企点后台系统为您随机分配主机空间IP地址: 上图右侧红色框框里面那串数字就是IP地址，这个IP地址是随机分配的，请以你看到的IP地址为准。 1、什么是域名绑定？ 域名绑定之后并且做完域名解析，浏览者就可以直接通过设置好的域名直接访问了， 例如：在微企点后台中点击“添加域名”，填写.wqdian.，设置之后就可以直接通过该域名访问到您的。 域名绑定在微企点后台完成 2、什么是域名解析？ 域名解析是把域名指向IP，让人们通过注册的域名可以方便地访问到一种服务。IP地址是网络上标识站点的数字地址， 为了方便记忆，采用域名来代替IP地址标识站点地址。域名解析就是域名到IP地址的转换过程。域名的解析工作由DNS服务器完成。 域名解析在域名注册商后台或解析服务后台完成 提示：对于先绑定域名还是先域名解析，并没有定论，但建议先进行域名绑定操作。 3、如何设置解析域名？ 这里以万网、易名、新网、西部数码、时代互联为例。 特别提醒：www和不带www的网址需要分别解析 一、记录类型「A记录」（要将域名指向主机服务商提供的IP地址，请选择「A记录」）
1、万网 1）首先登录，进入会员中心，点击左侧“我的域名”，选择对应域名后方的“解析”，进入域名解析界面 2）域名解析界面，点击“进入高级设置” 3）进入域名解析高级设置界面 第1步：点击“添加解析” 第2步：选择记录类型“A”记录，设置主机记录为所需容. 第3步：填写记录值 (该IP是微企点为您提供的主机空间IP地址，方法请见上方文章顶端)
完成以上3项后，点击“保存”。一般10分钟到两个小时便可以解析完成。最长不超过6个小时。 备注：TTL指各地DNS缓存您域名记录信息的时间，默认为10分钟（600）。 2、易名 1）、首先登录，点击左上角的“用户名”进入管理中心。 2）、点击管理中心左侧的“域名管理”，点击对应域名后的“解析”
动物运动方式的多样性教案2(苏教版八年 级下册) 《动物运动方式的多样性》的教学设计 一、教材结构与内容地位简析 《新生物课程标准》课程内容的设定是以“人与生物圈”为主线，精选了十个主题，即①科学探究；②生物与环境；③生物体的结构层次；④生物圈中的绿色植物；⑤生物圈中的人；⑥生物的生殖、发育与遗传；⑦动物的运动和行为；⑧生物的多样性；⑨生物技术；⑩健康的生活。而“动物运动方式的多样性”是新课标的第六大主题《动物的运动和行为》中的具体内容之一，它被编排在苏教版义务教育课程标准实验教科书生物八年级上册的第6单元《动物的运动和行为》的第16章《动物的运动》的首节。介绍了动物运动的各种方式及动物运动的意义。于前一章节学习了遗传和变异的有关知识，因此学生可以理解于自然环境的复杂多变，动物在长期的进化过程中，逐渐形成了独特的运动器官，从而扩大了活动范围，提高了适应环境的能力.同学们对动物的运动方式不会感到陌生，这方面的知识和经验积累应当很丰富，通过本节的学习之后，可以为后面《动物的行为》的学习起到了很好铺垫作用。 二、教学目标
根据上述教材结构与内容分析，考虑到学生已有的认知结构心理特征，我制定了如下教学目标： 1．基础知识目标：举例说出动物运动方式的多样性和动物运动的重要性。 2．能力目标：培养学生的观察能力，收集和处理信息的能力，分析和解决问题的能力以及交流与合作能力。 3．情感目标：通过学生对动物运动方式的了解，使同学们能更加关注自然界的动物，让他们能与之和谐相处，彼此成为永远的朋友，并深刻理解人与自然和谐发展的意义，提高环境保护意识。 三、教学重点、难点 本节是学生学习本章甚至是本单元的基础，动物运动知识对学生认识动物的本质特征非常重要，动物的运动依赖于一定的结构，动物的结构与功能是统一的。所以重点是要能举例说出动物运动方式的多样性。于动物的行为是一种本能的无意识的行为，是自然选择过程中长期进化的结果。因此，要理解动物运动的意义对学生来说是一个难点。 四、教法：在立足于课堂教学同时，要注意引导学生到大自然中去观察动物的运动，这样既满足了学生的好奇心又可激发学生的求知欲，同时培养了学生的观察能力、动手能力，更重要的是教给了学生探究生物世界的方法，同时增强了学生关爱生命、热爱大自然的意识。
[初二理化生]第一节动物运动方式的多样性
第一节动物运动方式的多样性 教材分析 本节内容介绍了动物运动方式的多样性和动物运动的意义。教学内容充分联系了学生的日常生活，但又不局限于日常生活中所见的动物类型。教学内容需要学生充分收集资料并加以合作讨论学习。经过学习，要求学生能掌握探究生物世界的方法，并培养学生热爱大自然，热爱生命的意识。并为后期学习动物运动的生理基础打下坚实的基础。 教学目标 1、知识与能力： 举例说出动物的运动方式的多样性； 举例说明动物运动的重要性。 2、过程与方法： 培养学生的观察能力； 提高学生的分析问题及表达交流的能力。 3、情感、态度与价值观： 通过活动增强学生的热爱大自然和关爱生命的意识。 学情分析 学生在日常生活中已经积累了一定的生物学知识，对常见动物的运动方式也已经比较了解。但是由于学
生个体差异的存在，学生之间知识了解的范围和情况也各自不同。所以充分利用讨论合作学习的方式来做到知识的共享。教师的重点是组织学生分析和整理资料，并注意在教学过程中充分渗透热爱生命，关爱大自然的思想。 课时分配 1课时 教学设计 教学准备 1、教师准备：教师收 集有关动物运动方式 的视频资料，并制作PPT等 2、学生准备：预习本 节课，收集有关动物运 动方式的资料 教学重、难点 重点：举例说出动物的 运 动 方 式 的 多 样 性 。举例说明动物 运 动 的 重 要 性 。 难点：说明动物运动的
重要性。 教学过程 （一）创设情境，走近课堂 师：动物是大家的朋友，我们在语文课中也学到了很多有关动物的成语，大家能不能来举出一些呢？ 生：动如脱兔、呆若木鸡、守株待兔、一丘之貉、狼狈为奸、狐假虎威、莺歌燕舞、龙腾虎跃、鹬蚌相争渔翁得利、螳螂捕蝉黄雀在后、螳臂当车…… 师：这些成语中有很多都反映了动物的运动 方式。你能不能说出来呢？ 生：有鸟在飞，老虎奔跑…… 师：大家说得不错，那么生活在不同环境中的动物在运动方式上又有什么特点呢？ （二）讨论合作，进入课堂 过渡：不同的动物有着不同的运动方式，但是也有的会有一定的相同之处，这是由什么决定的呢？ 首先，请同学们以小组为单位，分别讨论生活在陆地、水中、空中和能够生活在多种环境中动物的运动方式。 1、动物运动方式
域名解析服务器，在某些应用程序中如果手工设定合适的DNS服务器IP地址，则可避免程序自动检测，从而提高连接效率。那么如何查看所在地区DNS域名服务器的IP地址呢？答:在Windows XP环境下的查看方法如下 第一步，在开始菜单的“运行”对话框中输入“command”或“cmd”(引号不输入)，打开命令行窗口。 第二步，输入“Ipconfig /all”单击回车键后，屏幕上将显示出IP地址的相关信息。最后的两行，即“DNS Servers”后的内容就是本地DNS服务器的IP地址。 DNS 定义 DNS 是域名系统(Domain Name System) 的缩写，该系统用于命名组织到域层次结构中的计算机和网络服务。DNS 命名用于Internet 等TCP/IP 网络中，通过用户友好的名称查找计算机和服务。当用户在应用程序中输入DNS 名称时，DNS 服务可以将此名称解析为与之相关的其他信息，如IP 地址。因为，你在上网时输入的网址，是通过域名解析系解析找到相对应的IP地址，这样才能上网。其实，域名的最终指向是IP。 在IPV4中IP是由32位二进制数组成的，将这32位二进制数分成4组每组8个二进制数，将这8个二进制数转化成十进制数，就是我们看到的IP地址，其范围是在1～255之间。因为，8个二进制数转化为十进制数的最大范围就是1～255。现在已开始试运行、将来必将代替IPV6中，将以128位二进制数表示一个IP地址。 大家都知道，当我们在上网的时候，通常输入的是如：https://www.doczj.com/doc/e312310785.html,这样子的网址，其实这就是一个域名，而我们计算机网络上的计算机彼此之间只能用IP地址才能相互识别。再如，我们去一WEB服务器中请求一WEB页面，我们可以在浏览器中输入网址或者是相应的IP地址，例如我们要上新浪网，我们可以在IE的地址栏中输入： https://www.doczj.com/doc/e312310785.html,也可输入这样子218.30.66.101 的IP地址，但是这样子的IP地址我们记不住或说是很难记住，所以有了域名的说法，这样的域名会让我们容易的记住。 DNS：Domain Name System 域名管理系统域名是由圆点分开一串单词或缩写组成的，每一个域名都对应一个惟一的IP地址，这一命名的方法或这样管理域名的系统叫做域名管理系统。 DNS：Domain Name Server 域名服务器域名虽然便于人们记忆，但网络中的计算机之间只能互相认识IP地址，它们之间的转换工作称为域名解析（如上面的 https://www.doczj.com/doc/e312310785.html,与218.30.66.101 之间的转换），域名解析需要由专门的域名解析服务器来完成，DNS就是进行域名解析的服务器。 1、什么是DNS？ DNS是指：域名服务器(Domain Name Server)。在Internet上域名与IP地址之间是一一对应的，域名虽然便于人们记忆，但机器之间只能互相认识IP地址，它们之间的转换工作称为域名解析，域名解析需要由专门的域名解析服务器来完成，DNS就是进行域名解析的服务器。 2、为什么要注册DNS，有什么意义？ 申请了DNS后，客户可以自己为域名作解析,或增设子域名.客户申请DNS时，建议客户一次性申请两个。 3、在域名注册机构注册DNS的步骤及其注册的有关规定是什么？ 目前国际域名的DNS必须在国际域名注册商处注册，国内域名的DNS必须在CNNIC 注册。
第十六章动物的运动和行为 第一节动物运动方式的多样性 一、教学目标 1、培养学生的观察能力，收集和处理信息的能力，分析和解决问题的能力以及交流与合作能力。 2、通过学生对动物运动方式的了解，使同学们能更加关注自然界的动物，让他们能与之和谐相处，彼此成为永远的朋友，并深刻理解人与自然和谐发展的意义，提高环境保护意识。 二、重点难点 举例说出动物运动方式的多样性；举例说明动物运动的重要性。 三、教学资源 多媒体 四、教学设计 在开始时，首先激发学生的学习兴趣，利用精美的引人入胜的画面让学生去感悟，去发现。然后通过观察，合作交流等活动，让学生认知动物运动方式的多样性，理解动物运动的意义，增强保护动物的意识。 五、教学过程 【导入新课】 人们常说：“海阔凭鱼跃，天高任鸟飞。”不同的动物有着不同的运动方式。鹰击长空、鱼翔浅坻、麋鹿奔跑、企鹅游弋等等构成了大自然动态的美丽画卷。 下面我们先来欣赏一段大自然中动物运动的片段。 多媒体展示视频 自然界中各种动物的运动 通过刚才的欣赏你看到了什么？有什么感受？ 激起学生的好奇心和求知欲，激发学习的主动性，提高学习兴趣。 感受自然界中动物运动方式的多样性。说出动物在运动并感受大自然的美。 【授课】 一、动物运动方式的多样性 大自然真是多姿多彩，令人赏心悦目。草木荣枯，候鸟去来，蚂蚁搬家，蜻蜓低飞。动物的运动是大自然最丰富也是最有韵律的动态语言。 动物的运动方式多种多样，由于生活环境的不同运动方式也不同。经过交流，引导学生举
例说出动物的运动方式有哪些？（按照活动区域，说出动物的运动方式：空中的有飞行、滑翔；陆地上的有爬行、奔跑、跳跃、攀缘、行走等；水中的有游泳、漂浮等。） 主要活动区域运动方式 空中 陆地 水中 二、描述动物的运动 动物的运动让我们感受到了大自然无穷的魅力，下面请几个同学描述几种动物的运动。 自然界中的各种动物的运动都有着自己的韵律和美感。现在我们亲自观察几种动物的运动。注意观察动物的运动方式？如何完成运动的？ 引导学生形象描述几种动物的运动方式及如何完成运动的。 不同生活环境中的动物运动方式也不同，水中生活的动物主要依靠游泳、漂浮，陆地上的动物可以有行走、爬行、奔跑、跳跃、攀援等多种运动方式，空中生活的动物主要是飞行、滑翔。不同的运动方式不仅适应于不同的生活环境，而且在动物的身体内也有不同的结构与之相适应。 三、多媒体展示视频 让我们来欣赏大自然中丰富多彩的动物运动。请你说出各种动物的运动方式。 引导学生观看视频：狐狸的跳跃、海牛的游泳、水母的漂浮、鱼的游泳、豹子的奔跑、松鼠的攀缘、袋鼠的跳跃、乌贼的游泳、鹦鹉螺的漂浮、蜗牛的爬行、天鹅的水上奔跑等。 四、动物通过运动主动地适应环境 人也是动物，当今大规模的运动会，运动项目不下数十种。例如游泳，便有自由泳、蛙泳、仰泳等，有些显然是模仿动物。人虽然不会飞，但人类用自己的聪明才智发明了飞机、火箭，比任何动物都能远走高飞。 动物的运动对动物的生存有什么意义呢？我们先来欣赏一段视频。 引导学生观看视频：视频一：热带雨林中的蜥蜴在水面上奔跑 视频二：水獭的游泳、滑行、奔跑、行走 视频三：斑马的迁徙 分析讨论： 分析蜥蜴能在水面上奔跑对它有什么意义；
动物运动方式的多样 性
第一节动物的运动方式的多样性 资料16-1-1 动物三种运动方式的比较 资料16-1-2 各种动物的运动方式 资料16-1-3 鸟儿为什么会飞 资料16-1-4 鸟类的飞行 资料16-1-5 “天空王子”的飞行器——鸟翅 资料16-1-6 鸟的迁徙 资料16-1-7 动物的迁徙 资料16-1-1动物三种运动方式的比较 奔跑、飞行和游泳是动物最常采用的三种运动方式。大小不同的动物，其最小移动能耗速度及其能耗率是不一样的，通过测定各种不同大小的动物在最小移动能耗速度下的能耗率，我们就可以对三种运动方式的能量消耗情况进行比较。动物的游泳、飞行和奔跑三种运动方式在移动相同距离时的能量消耗是不一样的。 游泳是消耗能量最少的一种运动方式，因为动物在水中浮沉几乎不需要消耗能量，主要是依靠浮力调节。其次是飞行，飞行是借助于高速度下的高能耗率来获得其运动效果的。相比之下，在陆地上移动是最消耗能量的一种运动方式。在这里应当注意的是：对于每一种运动方式来说，虽然每克体重的最小移动能耗都随着动物体重的增加而减少，但就每只动物的最小移动能耗总值来
说，却随着动物体重的增加而增加。这其中的道理是很明显的，想必读者都十分清楚。 资料16-1-2 各种动物的运动方式 兽类最大的特点是行走和奔跑： 一般四肢动物的行动规律有这样的方式，以马为例，开始起步时如果是右前足先向前开步，对角线的左足就会跟着向前走，接着是左前足向前走再就是右足跟着向前走，这样就完成一个循环。接着又是另一次右前足向前，左后足跟着向前，左前足向前，右后足跟着，继续循环下去，就形成一个行走的运动。马除了走步外，还有小跑、快跑、奔跑等方式，各种跑的方式都有一定的运动规律的。 青蛙： 青蛙和鱼不一样，它是既能生活在水里，又能生活在陆地上的动物。当它在水中游水时，用长而有蹼的强大后肢划水游泳；当它在陆地上时，用肌肉发达的强大后肢跳跃。 跳跃是青蛙最主要的活动方式，身体结构也朝向适应跳跃的方向发展。青蛙的后肢比前肢长很多，修长的后肢是名副其实的弹簧腿产生往前冲的力量，比较短的前肢则能减轻落地后的冲击力。跳跃的原理如同压扁的弹簧放松之后往外弹跳出去，而后肢的大腿、小腿及足部平常坐叠在一起就具有压扁的弹簧功能。为了跳更远，腰部的肠骨特别延长和相接并形成可动关节，这样子青蛙跳出去以后，身体拉长更有冲力。长而有蹼的后肢也有助于游泳，让他们能够悠游于水陆两种环境。
第一节动物运动方式的多样性 教材分析 本节内容介绍了动物运动方式的多样性和动物运动的意义。教学内容充分联系了学生的日常生活，但又不局限于日常生活中所见的动物类型。教学内容需要学生充分收集资料并加以合作讨论学习。经过学习，要求学生能掌握探究生物世界的方法，并培养学生热爱大自然，热爱生命的意识。并为后期学习动物运动的生理基础打下坚实的基础。 教学目标 1、知识与能力： 举例说出动物的运动方式的多样性； 举例说明动物运动的重要性。 2、过程与方法： 培养学生的观察能力； 提高学生的分析问题及表达交流的能力。 3、情感、态度与价值观： 通过活动增强学生的热爱大自然和关爱生命的意识。 学情分析 学生在日常生活中已经积累了一定的生物学知识，对常见动物的运动方式也已经比较了解。但是由于学生个体差异的存在，学生之间知识了解的范围和情况也各自不同。所以充分利用讨论合作学习的方式来做到知识的共享。教师的重点是组织学生分析和整理资料，并注意在教学过程中充分渗透热爱生命，关爱大自然的思想。 课时分配 1课时 教学设计 教学准备 1、教师准备：教师收集有关动物运动方式的视频资料，并制作PPT等 2、学生准备：预习本节课，收集有关动物运动方式的资料 教学重、难点 重点：举例说出动物的运动方式的多样性。 举例说明动物运动的重要性。 难点：说明动物运动的重要性。 教学过程 （一）创设情境，走近课堂 师：动物是大家的朋友，我们在语文课中也学到了很多有关动物的成语，大家能不能来举出一些呢？ 生：动如脱兔、呆若木鸡、守株待兔、一丘之貉、狼狈为奸、狐假虎威、莺歌燕舞、龙腾虎跃、鹬蚌相争渔翁得利、螳螂捕蝉黄雀在后、螳臂当车…… 师：这些成语中有很多都反映了动物的运动方式。你能不能说出来呢？生：有鸟在飞，老虎奔跑…… 师：大家说得不错，那么生活在不同环境中的动物在运动方式上又有什么特点呢？（二）讨论合作，进入课堂 过渡：不同的动物有着不同的运动方式，但是也有的会有一定的相同之处，这是由什么决定的呢？ 首先，请同学们以小组为单位，分别讨论生活在陆地、水中、空中和能够生活在多种环境中动物的运动方式。 1、动物运动方式的多样性 学生活动：四人为一小组，一个大组讨论生活在一种环境中的动物。在讨论的过程中，尽量说出有代表性的生物，并选出本小组的发言代表。时间为五分钟。 教师活动：在学生讨论的同时，参与各个小组的活动，指导学生
域名的解析过程中采用两种查询方式，其中需要注意的事项： 一、主机向本地域名服务器的查询一般都是采用递归查询。 所谓递归查询就是：如果主机所询问的本地域名服务器不知道被查询的域名的IP地址，那么本地域名服务器就以DNS客户的身份，向其它根域名服务器继续发出查询请求报文(即替主机继续查询)，而不是让主机自己进行下一步查询。 因此，递归查询返回的查询结果或者是所要查询的IP地址，或者是报错，表示无法查询到所需的IP地址。 二、本地域名服务器向根域名服务器的查询的迭代查询。 迭代查询的特点：当根域名服务器收到本地域名服务器发出的迭代查询请求报文时，要么给出所要查询的IP地址，要么告诉本地服务器：“你下一步应当向哪一个域名服务器进行查询”。 然后让本地服务器进行后续的查询。根域名服务器通常是把自己知道的顶级域名服务器的IP地址告诉本地域名服务器，让本地域名服务器再向顶级域名服务器查询。
顶级域名服务器在收到本地域名服务器的查询请求后，要么给出所要查询的IP地址，要么告诉本地服务器下一步应当向哪一个权限域名服务器进行查询。 最后，知道了所要解析的IP地址或报错，然后把这个结果返回给发起查询的主机。 三、递归查询和迭代查询的差别 1.下面举一个例子演示整个查询过程： 假定域名为https://www.doczj.com/doc/e312310785.html,的主机想知道另一个主机https://www.doczj.com/doc/e312310785.html,的IP地址。例如，主机https://www.doczj.com/doc/e312310785.html,打算发送邮件给https://www.doczj.com/doc/e312310785.html,。这时就必须知道主机https://www.doczj.com/doc/e312310785.html,的IP地址。下面是上图a的几个查询步骤：
①主机https://www.doczj.com/doc/e312310785.html,先向本地服务器https://www.doczj.com/doc/e312310785.html,进行递归查询。 ②本地服务器采用迭代查询。它先向一个根域名服务器查询。 ③根域名服务器告诉本地服务器，下一次应查询的顶级域名服务器https://www.doczj.com/doc/e312310785.html,的IP地址。 ④本地域名服务器向顶级域名服务器https://www.doczj.com/doc/e312310785.html,进行查询。 ⑤顶级域名服务器https://www.doczj.com/doc/e312310785.html,告诉本地域名服务器，下一步应查询的权限服务器https://www.doczj.com/doc/e312310785.html,的IP地址。 ⑥本地域名服务器向权限域名服务器https://www.doczj.com/doc/e312310785.html,进行查询。 ⑦权限域名服务器https://www.doczj.com/doc/e312310785.html,告诉本地域名服务器，所查询的主机的IP地址。 ⑧本地域名服务器最后把查询结果告诉https://www.doczj.com/doc/e312310785.html,。 2.关于DNS解析的TTL参数： 我们在配置DNS解析的时候，有一个参数常常容易忽略，就是DNS解析的TTL参数，Time To Live。TTL这个参数告诉本地DNS服务器，域名缓存的最长时间。用阿里云解析来举例，阿里云解析默认的TTL是10分钟，10分钟的含义是，本地DNS服务器对于域名的缓存时间是10分钟，10分钟之后，本地DNS服务器就会删除这条记录，删除之后，如果有用户访问这个域名，就要重复一遍上述复杂的流程。
青岛版小学科学六年级上册 13、《动物的运动》教学设计 张春梅 济宁市洸河路小学
13、《动物的运动》教学设计 一、教学目标： 科学知识目标： 认识水生动物的主要运动方式是游泳，陆生动物的主要运动方式是爬行、行走、跳跃和奔跑，空中生活的动物的主要运动方式是飞行。 科学探究目标： 1、认识物体运动方式的多样性； 2、能说出常见物体的运动方式，观察分析器运动规律； 3、能够准确地比较常见物体运动速度的快慢； 4、分析探究动物的运动对于动物个体和种族的生存具有怎样的重要意义； 5、能用各种感官对物体的运动进行观察，能用图或文字表述；会查阅书刊及其他信息源；能选择自己擅长的方式表述研究过程和结果。 情感、态度和价值观目标： 1、引导学生自觉运用合作与交流的学习方法； 2、培养学生注意观察、善于观察和分析推理的能力； 3、意识到人与自然要和谐相处，愿意合作与交流。 二、教学重难点： 重点：认识不同动物的运动方式的不同特点。 难点：知道动物运动方式具有与其生活环境相适应的特点； 三、教学方法： 讲述、合作探究相结合 四、教学准备： 教师：多种动物的运动图片资料 学生：搜集与动物运动有关的资料。 五、课时安排： 1课时 六、教学过程：
课前谈话: 同学们，你们喜欢小动物吗？你能说一说它们是怎样运动的吗？激发学生去思考、回忆不同动物的各种运动方式。 （一）创设情境，引入新课 1、同学们，老师也很喜欢小动物，课前老师还搜集了一些小动物运动的视频资料，我们一起来看一看。（出示课件：从电视节目《动物世界》下载的视频资料） 2、同学们，在地球上，生活着很多很多的小动物，今天，我们学习《动物的运动》这节课，一起来探讨不同的动物具有的不同运动方式和规律。 （二）小组自行探究 1.陆地动物的运动方式。 师：生活中我们经常见到运动。你曾经见过生活在陆地的动物都有哪些运动方式？ 小组内先自行交流，然后全班汇报。 师：老师也搜集了一部分在陆地上生活的动物的运动方式，我们一起来看大屏幕。（课件出示：孩子们很少见到的陆地动物的运动方式） 这些动物的运动方式有什么共同特点？ 学生讨论后交流，教师小结并板书：爬行、行走、奔跑、跳跃 2. 水中动物的运动方式。 师：你曾经见过的生活在水中的动物都有哪些运动方式？ 生：游泳 教师随机板书：游泳 师：对，但是它们游泳的方式也各不相同。谁能模仿几种鱼类的游泳方式？学生交流 3. 空中飞行动物的运动方式。 师：你又曾经见过生活在空中的动物都有哪些运动方式？ 生：飞行
第一节动物的运动方式的多样性 资料16-1-1 动物三种运动方式的比较 资料16-1-2 各种动物的运动方式 资料16-1-3 鸟儿为什么会飞 资料16-1-4 鸟类的飞行 资料16-1-5 “天空王子”的飞行器——鸟翅 资料16-1-6 鸟的迁徙 资料16-1-7 动物的迁徙 资料16-1-1动物三种运动方式的比较 奔跑、飞行和游泳是动物最常采用的三种运动方式。大小不同的动物，其最小移动能耗速度及其能耗率是不一样的，通过测定各种不同大小的动物在最小移动能耗速度下的能耗率，我们就可以对三种运动方式的能量消耗情况进行比较。动物的游泳、飞行和奔跑三种运动方式在移动相同距离时的能量消耗是不一样的。 游泳是消耗能量最少的一种运动方式，因为动物在水中浮沉几乎不需要消耗能量，主要是依靠浮力调节。其次是飞行，飞行是借助于高速度下的高能耗率来获得其运动效果的。相比之下，在陆地上移动是最消耗能量的一种运动方式。在这里应当注意的是：对于每一种运动方式来说，虽然每克体重的最小移动能耗都随着动物体重的增加而减少，但就每只动物的最小移动能耗总值来说，却随着动物体重的增加而增加。这其中的道理是很明显的，想必读者都十分清楚。 资料16-1-2 各种动物的运动方式 兽类最大的特点是行走和奔跑： 一般四肢动物的行动规律有这样的方式，以马为例，开始起步时如果是右前足先向前开步，对角线的左足就会跟着向前走，接着是左前足向前走再就是右
足跟着向前走，这样就完成一个循环。接着又是另一次右前足向前，左后足跟着向前，左前足向前，右后足跟着，继续循环下去，就形成一个行走的运动。马除了走步外，还有小跑、快跑、奔跑等方式，各种跑的方式都有一定的运动规律的。
域名解析过程及原理 域名解析过程： 第一步：客户机提出域名解析请求,并将该请求发送给本地的域名服务器。 第二步：当本地的域名服务器收到请求后,就先查询本地的缓存,如果有该纪录项,则本地的域名服务器就直接把查询的结果返回。 第三步：如果本地的缓存中没有该纪录,则本地域名服务器就直接把请求发给根域名服务器,然后根域名服务器再返回给本地域名服务器一个所查询域(根的子域)的主域名服务器的地址。 第四步：本地服务器再向上一步返回的域名服务器发送请求,然后接受请求的服务器查询自己的缓存,如果没有该纪录,则返回相关的下级的域名服务器的地址。 第五步：重复第四步,直到找到正确的纪录。 第六步：本地域名服务器把返回的结果保存到缓存,以备下一次使用,同时还将结果返回给客户机。 让我们举一个例子来详细说明解析域名的过程.假设我们的客户机如果想要访问站点：https://www.doczj.com/doc/e312310785.html, ,此客户本地的域名服务器是https://www.doczj.com/doc/e312310785.html, ,一个根域名服务器是https://www.doczj.com/doc/e312310785.html, ,所要访问的网站的域名服务器是https://www.doczj.com/doc/e312310785.html,,域名解析的过程如下所示: (1)客户机发出请求解析域名https://www.doczj.com/doc/e312310785.html,的报文 (2)本地的域名服务器收到请求后,查询本地缓存,假设没有该纪录,则本地域名服务器https://www.doczj.com/doc/e312310785.html,则向根域名服务器https://www.doczj.com/doc/e312310785.html,发出请求解析域名https://www.doczj.com/doc/e312310785.html, (3)根域名服务器https://www.doczj.com/doc/e312310785.html,收到请求后查询本地记录得到如下结果:https://www.doczj.com/doc/e312310785.html, NS https://www.doczj.com/doc/e312310785.html,（表示https://www.doczj.com/doc/e312310785.html,域中的域名服务器为：https://www.doczj.com/doc/e312310785.html,）,同时给出https://www.doczj.com/doc/e312310785.html,的地址,并将结果返回给域名服务器https://www.doczj.com/doc/e312310785.html,。 (4)域名服务器https://www.doczj.com/doc/e312310785.html,收到回应后,再发出请求解析域名https://www.doczj.com/doc/e312310785.html, 的报文。 (5)域名服务器 https://www.doczj.com/doc/e312310785.html,收到请求后,开始查询本地的记录，找到如下一条记录:https://www.doczj.com/doc/e312310785.html, A 211.120.3.12（表示https://www.doczj.com/doc/e312310785.html,域中域名服务器https://www.doczj.com/doc/e312310785.html, 的IP地址为:211.120.3.12）,并将结果返回给客户本地域名服务器https://www.doczj.com/doc/e312310785.html,。