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• avformat/segment : populate empty outer stream extradata from packet

  21 mai 2019, par Gyan Doshi

  avformat/segment : populate empty outer stream extradata from packet
  At present, if the outer stream extradata is empty but first packet
  
  has extradata as a side data element, then only the first segment's
  
  muxer instance may be able to extract this side data and use it.
  
  For all other segments, extradata in packet side data could be missing
  
  and generated segments may be invalid or unplayable in some apps
  
  e.g. for an ADTS AAC stream segmented to MP4, the adtstoasc BSF will
  
  add extradata to the first packet. The MOV muxer for the first segment
  
  will add this to codecpar for the inner stream and write
  
  Decoder Specific Information within the esds box. For other segments,
  
  their esds' will not have this decSpecificInfo and they can't be opened
  
  in Quicktime player or by services like nginx-vod-module.
  

  • [DH] libavformat/segment.c

• avcodec/jpeg2000dec : Skip de-quantization of empty areas

  19 mars 2019, par Michael Niedermayer

  avcodec/jpeg2000dec : Skip de-quantization of empty areas
  Fixes : Timeout (26sec -> 18sec)
  
  Fixes : 13448/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_JPEG2000_fuzzer-576903098243481
  Found-by : continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
  
  Signed-off-by : Michael Niedermayer <michael@niedermayer.cc>
  

  • [DH] libavcodec/jpeg2000dec.c

• OpenCV returns an Empty Frame on video.read

  20 mars 2019, par Ikechukwu Anude

  Below is the relevant code

  import cv2 as cv
  
  import numpy as np
  
  
  
  video = cv.VideoCapture(0) #tells obj to use built in camera\
  
  
  
  #create a face cascade object 
  
  face_cascade  = 
  
  cv.CascadeClassifier(r"C:\Users\xxxxxxx\AppData\Roaming\Python\Python36\site- 
  
  packages\cv2\data\haarcascade_frontalcatface.xml")
  
  
  
  a = 1
  
  #create loop to display a video
  
  while True:
  
      a = a + 1
  
      check, frame = video.read()
  
      print(frame)
  
  
  
      #converts to a gray scale img
  
      gray = cv.cvtColor(frame, cv.COLOR_BGR2GRAY)
  
  
  
      #create the faces
  
      faces = face_cascade.detectMultiScale(gray, scaleFactor=1.5, minNeighbors=5)
  
  
  
      for(x, y, w, h) in faces:
  
          print(x, y, w, h)
  
  
  
      #show the image
  
      cv.imshow('capturing', gray)
  
  
  
      key = cv.waitKey(1) #gen a new frame every 1ms
  
  
  
      if key == ord('q'): #once you enter 'q' the loop will be exited
  
          break
  
  
  
  print(a) #this will print the number of frames
  
  
  
  #captures the first frame
  
  video.release() #end the web cam
  
  
  
  #destroys the windows when you are not defined
  
  cv.destroyAllWindows()

  The code displays a video captured from my webcam camera. Despite that, OpevCV doesn’t seem to be processing any frames as all the frames look like this

   [[0 0 0]
  
    [0 0 0]
  
    [0 0 0]
  
    ...
  
    [0 0 0]
  
    [0 0 0]
  
    [0 0 0]]]

  which I assume means that they are empty.

  This I believe is preventing the algorithm from being able to detect my face in the frame. I have a feeling that the issue lies in the ffmpeg codec, but I’m not entirely sure how to proceed even if that is the case.

  OS : Windows 10
  Language : Python

  Why is the frame empty and how can I get OpenCV to detect my face in the frame ?