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• Why opencv can open video but failed to retrieve frame from it ?

  20 février 2013, par Greper

  I build opencv with ffmpeg support and this is a snippet of my code to read a video and iterate through the frames.

  if (argc != 3) {
  
      std::cout<<"Usage: exe input_video_filename skip_frames \n"< scores;
  
  while(true)
  
  {
  
      if(!**cap.retrieve(frame)**)
  
      {
  
          std::cout<<"error retrieve frame"<code>

  The program succeed to read the video at line cap.open(video_fn) but fail to retrieve frame from VideoCapture at the line if(!cap.retrieve(frame)). I tried with mp4 and avi but it always fails.Does anyone encountered similar problem ? How to solve it ? Many thanks !

• IContainer.open() fails when using with custom ByteChannel to read from

  13 août 2014, par AnilJ

  I am trying to open an IContainer object which is reading from a custom input buffer rather than reading from a media file. The implementation for this custom input buffer is as below.

  The code to create and open the container is as below.

  // Open up the container for READING
  
  mInputCStore = new CStore();
  
  
  
  IContainerFormat format = IContainerFormat.make();
  
  if (format.setInputFormat("flv") < 0) {
  
      throw new IllegalArgumentException("Failed to initialize the input format");
  
  }
  
  
  
  // Open up the container
  
  mInputContainer = IContainer.make();
  
  int retval = mInputContainer.open(mPlaybackContainerStore, IContainer.Type.READ, format);       
  
  if (retval < 0) {
  
      // This little trick converts the non friendly integer return value into  
  
      // a slightly more friendly object to get a human-readable error name
  
      IError error = IError.make(retval);
  
      throw new IllegalArgumentException("could not open input container: " + mPlaybackContainerStore + "; Error: " + error.getDescription());
  
  }

  The above code throwing an exception saying that —

  Exception in thread "main" java.lang.IllegalArgumentException: could not open input container: com.client.video.ContainerStore@61981853; Error: Operation not permitted

  The same custom buffer when used while writing to the container is working successfully. Can someone pls help me understand what is missing in the custom buffer implementation, as far as using it in READ mode and why the reason it is failing ?

  package test;
  
  
  
  import java.io.IOException;
  
  import java.nio.ByteBuffer;
  
  import java.nio.channels.ByteChannel;
  
  import java.util.concurrent.ConcurrentLinkedQueue;
  
  
  
  public class CStore implements ByteChannel {
  
      private ConcurrentLinkedQueue<datachunk> mChunkQueue = null;
  
      private int mQueueSize = 0;
  
  
  
      // constructor
  
      public CStore(String type) {
  
          mQueueSize = 0;
  
          mChunkQueue = new ConcurrentLinkedQueue<datachunk>();
  
          mChunkQueue.clear();
  
      }
  
  
  
      @Override
  
      public void close() throws IOException {
  
          return;
  
      }
  
  
  
      @Override
  
      public boolean isOpen() {
  
          return false;
  
      }
  
  
  
      @Override
  
      public int write(ByteBuffer buffer) throws IOException {
  
          DataChunk chunk = new DataChunk(buffer);
  
          mChunkQueue.add(chunk);
  
          mQueueSize += chunk.getLength();
  
          return 0;
  
      }
  
  
  
      public int read(ByteBuffer buffer) throws IOException {
  
  
  
          int result = 0;
  
  
  
          DataChunk chunk = mChunkQueue.poll();
  
          if (chunk != null) {
  
              buffer = chunk.getBuffer();
  
              if (buffer != null) {
  
                  result = 0;
  
              } else {
  
                  result = 1;
  
              }
  
          }
  
  
  
          return result;
  
      }
  
  }
  
  </datachunk></datachunk>

• I had split 420 yuv file to 420_y 420_u 420_v, how to open the three files ?

  1er février 2018, par KentJimmy

  I simplest splite yuv 420 file to three files:y, u, v, by use code :

  int simplest_yuv420_split(char *url, int w, int h,int num){
  
      FILE *fp=fopen(url,"rb+");  
  
      FILE *fp1=fopen("output_420_y.y","wb+");  
  
      FILE *fp2=fopen("output_420_u.y","wb+");  
  
      FILE *fp3=fopen("output_420_v.y","wb+");  
  
    
  
      unsigned char *pic=(unsigned char *)malloc(w*h*3/2);  
  
    
  
      for(int i=0;i2,fp);  
  
          //Y  
  
          fwrite(pic,1,w*h,fp1);  
  
          //U  
  
          fwrite(pic+w*h,1,w*h/4,fp2);  
  
          //V  
  
          fwrite(pic+w*h*5/4,1,w*h/4,fp3);  
  
      }  
  
    
  
      free(pic);  
  
      fclose(fp);  
  
      fclose(fp1);  
  
      fclose(fp2);  
  
      fclose(fp3);  
  
    
  
      return 0;  
  
  }

  I can open the original file by ffplay using commend
  ffplay -f rawvideo -pixel_format yuv420p -video_size 640x360 -i graybar_640x360.yuv

  now I want to open the splited file output_420_y.y

  When I run commend
  ffplay -f rawvideo -pixel_format yuv420p -video_size 256x256 -i output_420_v.y

  show error :
  [rawvideo @ 0x7fab5283ea00] Invalid buffer size, packet size 16384 < expected frame_size 98304

  I know this means the file output_420_v.y is part of original as 1/6.

  anyone can show me how to open this ?

  thanks.