StreamingMedia's Experiment And Development Platform Based On DirectShow Technology

Streaming Media is a kind of newly network transformingtechnique used of transforming and playing sequential time_based datastream of multimedia like video or sound and etc. It consists ofgathering streaming media and video/ sound's coding anddecoding,saving,transforming,playing and etc. The development of theInternet comes to a decision the vast foreground of Streaming Media'smarket, the application of Streaming Media technique will bring therevolution variety for the network information, bring about profoundinfluence on the people's work and lifes.For the sake of the better development of the Streaming Mediaapplications, the Microsoft company developed and announced thetechnique of DirectShow providing a kind of developmentenvironment of open type, defining how to use standard module calledfilter to handle the streaming media data.Using the Filter GraphManager to control the linking of a few basic types of filters andcontrol the fluxion of medium data between the filters , the generalprocess is linking orderly a source filter that collecting the video/sound's data ,a transform filter that carrying on the particular operationto the streaming media, a render filter that playing the video/ sound,and then, setting up a FilterGraph completing the application of thestreaming media.Developing a streaming medai's experiment and developmentplatform according to the DirectShow technique, can help us todevelop video/sound operation algorithm in the actual environmentwhere the streaming media application has been used, these algorithmspacked with the filter form can be used into the numerous applicationaccording to the DirectShow right away, the progress that speed thealgorithm to be used physically;On the other hand,numerousvideo/sound algorithms will expand the usage scope of the streamingmedia, strengthen its function quickly.This paper described three filters that we develop, by using thesemodules, enlarging the DirectShow to become a platform where mostvideo operation algorithms can be realized and tested, these filtersare:1.the AVI File Writer Filter,belonging to the render filter type.It cansave the collected data to a AVI file which according to the factualrequirement can be compressed or uncompressed,integrated orsegmented with time .Purpose that develops this filter first is providingAVI file,namely testing video data for testing the video operationalgorithms, the next in order to perfect the saving function of theDirectShow, the general player can play the file it save.2.the Compose Filter.belonging to the transform filter type.Accordingto the factual requirement, it composes three or two video stream intoone single steam and exports it.The inputting video can be from theAVI file stored in disk or from the vidicon, the video compositionalgorithm can be adjusted by modifying a particular function, it canalso change the size and color space of the stream based on procedurecontrol.The development of this filter not only has the important andactual use value, but also carries out one enter multi out mode, tryingthe synchronous control oftwo or several video streams, having makethe foundation for the further development of multi-stream'scooperation.The most important point is to develop a mechanism ofbufferring frames including mechanism of applying and releasing thememory,mechanism of applying and releasing the frame and arealization of stack that buffers the frame, among them, the memoryoperation pass two pools to moderate the operation mutually tocomplete, using one pool to manage the allotment and recoveries ofmemory applying object,the other to manage the allotment andrecoveries of memory object.such double layers pool structurespeeds process of applying the memory and economizes the usage ofmemory;Contrastively,the applying of frame based on the applying ofmemory, its dditional memory need is also very small, so using thesingle pool structure.The development of mechanism of bufferring notonly carried out composing the video stream, but also because thevideo operation is the operation to the video frame, most algorithmsneed to buffer the frame and then use the bufferred frames to distill theinformation by doing some operations like difference andcomparision.so after having this buffer mechanism,it can buffersystem-allow amount of frames and then operate them later in thefilters. it make the foundations of realizing these algorithms.3.the BackgroundExtraction Filter,belonging to the transform filtertype.It will eliminate the background and only reserve the foregroundpicture.For example,a person within room, picture of person will bedisplayed and the room's will be eliminate .Mainly develop this filteris for applying in the virtual video meeting, also is uses for seeing theeffect of the testing algorithm in the streaming testing platform.Thisfilter used two kinds of methods respectively, one kind is using themean of RGB to be the background, after comparison,extract theforeground according to the threshold.another kind render the samplein Y, and use 4*4 of piece to be the basic operation object, extract themean of Y of first n samples to be the background, aftercomparison,join the marking piece,merging and deleting the piece andetc.among them,the afterOperation has been used in the other testingplatform and can work normally. Compare these two kinds of methodscan see the first method can show the foreground quickly, but forstrengthenning the anti-noise,set the threshold more greatly, cause theforeground extraction not complete, the second kind can resist thesmaller noise, but the foreground outline is misty, the speed can'tmatch the actual usage standard.The end use three filters together to imitated the virtual video meetingapplication in the GraphEdit and in the amended ConferenceXPrespectively.Composing two video streams extracted the forground tobe a single stream and outputing it, its effect is that attendants ofmeeting in different place shows at same background (by thenetwork).Here the background is white only.The result of testing hasdisplayed the filter's running effect in the network platform.The experiments of filter single and the integration testing have proved,these filters that this paper descripts can attain its original designrequest, also basic satisfy the demand of the actual usage.