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• Realtime video processing with javacv on Android

  7 août 2014, par moonie

  I wish to do realtime video processing on Android using opencv/javacv. My basic approach can be summarized as follow :

  onCreate(), generating a new JavaCameraView

  mCameraView = new JavaCameraView(this, mCameraIndex);
  
  mCameraView.setCvCameraViewListener(this);   
  
  setContentView(mCameraView); 

  when the user clicks a button, a ffmpegframe recorder is created

  try{
  
              final long currentTimeMillis = System.currentTimeMillis();
  
              final String appName=getString(R.string.app_name);
  
              final String galleryPath=Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_PICTURES).toString();
  
              final String albumPath=galleryPath+"/"+appName;
  
              final String photoPath=albumPath+"/"+currentTimeMillis+".avi";
  
              FFmpegFrameRecorder recorder=FFmpegFrameRecorder.createDefault(photoPath, 640, 360);
  
              recorder.setFrameRate(30);
  
              recorder.start();
  
              }catch(FrameRecorder.Exception e){
  
              e.printStackTrace();
  
              }

  then for each CameraFrame, use the following code to process and save the frame

      public Mat onCameraFrame(final CvCameraViewFrame inputFrame){
  
      final Mat rgba = inputFrame.rgba();
  
      //...apply some filters on rgba
  
      if(mIsTakingVideo){
  
          try{
  
            recorder.record(MatToIplImage(rgba,640,320));           
  
          }catch(FrameRecorder.Exception {
  
              e.printStackTrace();
  
              }       
  
      }
  
      return rgba;
  
  }
  
  
  
   public IplImage MatToIplImage(Mat m){
  
    Bitmap bmp=Bitmap.createBitmap(m.width(), m.height(), Config.ARGB_8888);
  
    Utils.matToBitmap(m, bmp);
  
    IplImage image=IplImage.create(m.width(),m.height(),IPL_DEPTH_8U,1);
  
    bmp.copyPixelsToBuffer(image.getByteBuffer());
  
    return image;}

  When the user clicks the button again, the recorder is stopped and released. However the video I create is an empty video. Any idea why ?

  EDIT :
  The video was empty because the format avi is not supported on my test phone...
  Now the video is not empty but it has the following errors

  1. The recorded video has two split windows instead of just one window
  2. The color is very different from the object I recorded
  3. The play rate is too fast.

• How can I rename a file from a txt file with Windows bat file ?

  12 septembre 2022, par user1264599

  I have a batch script that renames a file to input.mkv so it can be processed by a string of other commands in the bat file with a final file called ProcessedVideo.mkv. I capture the OG file name using "dir *.mkv /b>OG_FileName.txt" before being renamed.

  


  How can I rename the final processed mkv file to the name captured in the OG_FileName.txt and maybe add "_Added-Text.mkv" as the last part of my Batch Script ? (Adding text to the file name is not that important if it is too much trouble).

  


  I really thought this would be easy but I'm defeated.

  


• Gallery of VP8 Encoding Naivete

  15 octobre 2010, par Multimedia Mike — VP8

  I’ve been toiling away as a multimedia technology generalist for so long that it’s easy for me to forget that not everyone is as versed in the minutiae of the domain as I am. But I recently experienced what it’s like to be such an outsider when I posted about my toy VP8 encoder, expressing that it’s one of the hardest things I have ever tried to do. I heard of from number of people who do have extensive experience in video encoding, particularly with the H.264 and VP8 codecs. Their reactions were predictable : What’s so hard ? Look, you might be a little too immersed in the area to really understand a relative beginner’s perspective.

  And to all the people who suggested that I should get the encoder into FFmpeg ASAP : Are you crazy ?! Did you see what the first pass of the encoder produced ? Do you have lower standards than even I do ?

  
  
  

  Not Giving Up
  I worked a little more on the toy encoder. Remember that the above image is what I’m hoping to encode somewhat faithfully for this experiment. In my first pass, I attempted vertical prediction for all planes. For my next pass, I forced the chroma planes to mid-level (which results in a greyscale image) and played with the 16×16 luma prediction modes. When implementing an extremely naive algorithm to decide which 16×16 prediction mode would be the best for a particular block, this is what the program produced :

  
  
  

  For fun, here is what the image encodes to when forcing various prediction modes :
  

  I think the DC-only prediction mode actually looks a little better than the image that the naive algorithm produced :

  
  
  

  Vertical 16×16 prediction, similar to the image from the last post (just in black and white) :
  

  
  
  

  Horizontal 16×16 prediction :
  

  
  
  

  This is the 16×16 prediction mode unique to VP8, the TrueMotion mode (based on On2/Duck’s very first video codec) :
  

  
  
  

  Wow, these encodings really bring down the cheerful tone of the original image.

  Next Steps
  I have little reason to believe that I am encoding and subsequently reconstructing the image correctly (i.e., error is likely propagating through the entire encoding). If I have time, the next step is to validate my reconstruction against the encoder. Then I need to get the entropy considerations correct so that I actually get some compression out of this format.