This example shows how to extract and visualize a video stream, stored in an ADTF DAT file. It also shows how to write the video stream into a video file.

Download the sample video DAT file.

downloadURL ='https://ssd.mathworks.com/supportfiles/driving/data/sample_can_video_dat.zip'; dataFolder = fullfile(tempdir,'adtf-video', filesep); options = weboptions('Timeout', Inf); zipFileName = [dataFolder,'sample_can_video_dat.zip']; folderExists = exist(dataFolder,'dir');% Create a folder in a temporary directory to save the downloaded file.if~folderExists mkdir(dataFolder); disp('Downloading sample_can_video_dat.zip (9.74 MB)...') websave(zipFileName, downloadURL, options);% Extract contents of the downloaded file.disp('Extracting sample_can_video_dat.zip...') unzip(zipFileName, dataFolder);end

Create the ADTF File Reader object.

datFileName = fullfile(dataFolder,"sample_can_video.dat"); fileReader = adtfFileReader(datFileName)

fileReader = DataFileName: "C:\Users\latriwal\AppData\Local\Temp\adtf-video\sample_can_video.dat" DescriptionFileName: "" PluginDirectory: "" StreamCount: 2 StreamInfo: StreamIndex StreamName StreamType StartTime EndTime ItemCount ___________ __________ _______________ _________ __________ _________ 1 {'rawcan'} {'UNSUPPORTED'} 0 sec 14.805 sec 743 2 {'video' } {'adtf/image' } 0 sec 14.799 sec 149

From theStreamInfoproperty, note that the index of the video stream is 2. Use theselectfunction of theadtfFileReaderobject, to select the video stream for reading. The returnedadtfStreamReaderobject has all the information about the selection.

streamReader = select(fileReader,2)

streamReader = adtfStreamReader with properties: DataFileName: "C:\Users\latriwal\AppData\Local\Temp\adtf-video\sample_can_video.dat" DescriptionFileName: "" PluginDirectory: "" StreamIndex: 2 StartIndex: 1 EndIndex: 149 CurrentIndexOffset: 0 StartTime: [0×0 duration] EndTime: [0×0 duration] DataCount: 149

Note that the value ofCurrentIndexOffsetis 0. This signifies that the nextreadNextcall will return the first item.

Preview the first image frame from the stream.

firstFrame = readNext(streamReader); imshow(firstFrame.Data.Item)

Before creating a video, use theresetfunction to start reading from the first frame. This resets the value ofCurrentIndexOffsetto 0.

reset(streamReader); fprintf("CurrentIndexOffset = %d\n",streamReader.CurrentIndexOffset)

CurrentIndexOffset = 0

创建一个VideoWriterobject that you can use to write image frames to a video file. Specify a frame rate of 1 frame per second.

videoWriterObj = VideoWriter("example_video.avi"); videoWriterObj.FrameRate = 1; open(videoWriterObj);

使用thestreamReaderobject, iterate over the data items in the selection one-by-one. ThehasNextfunction determines if there is an item left to read as we are incrementally reading the file.readNext返回的数据项基本上是一个结构re containing the data and the associated timestamp. In every iteration, extract the image frame and write it to the video file.

whilestreamReader.hasNext() streamData = streamReader.readNext(); imageFrame = streamData.Data.Item; frame = im2frame(streamData.Data.Item, gray); writeVideo(videoWriterObj, frame);end

Alternatively, you can read all the image frames at once, using thereadfunction, and iterate over it later.

allData = read(streamReader)

allData =struct with fields:StreamIndex: 2 Data: [149×1 struct]

Close the connection with the video file.

close(videoWriterObj); closeall

Visualize the output fileexample_video.aviusingVideo Viewer.

implay("example_video.avi")