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• How to obtain time markers for video splitting using python/OpenCV

  10 novembre 2018, par Bleddyn Raw-Rees

  I’m working on my MSc project which is researching automated deletion of low value content in digital file stores. I’m specifically looking at the sort of long shots that often occur in natural history filming whereby a static camera is left rolling in order to capture the rare snow leopard or whatever. These shots may only have some 60s of useful content with perhaps several hours of worthless content either side.

  As a first step I have a simple motion detection program from Adrian Rosebrock’s tutorial [http://www.pyimagesearch.com/2015/05/25/basic-motion-detection-and-tracking-with-python-and-opencv/#comment-393376]. Next I intend to use FFMPEG to split the video.

  What I would like help with is how to get in and out points based on the first and last points that motion is detected in the video.

  Here is the code should you wish to see it...

  # import the necessary packages
  
  import argparse
  
  import datetime
  
  import imutils
  
  import time
  
  import cv2
  
  
  
  # construct the argument parser and parse the arguments
  
  ap = argparse.ArgumentParser()
  
  ap.add_argument("-v", "--video", help="path to the video file")
  
  ap.add_argument("-a", "--min-area", type=int, default=500, help="minimum area size")
  
  args = vars(ap.parse_args())
  
  
  
  # if the video argument is None, then we are reading from webcam
  
  if args.get("video", None) is None:
  
  camera = cv2.VideoCapture(0)
  
  time.sleep(0.25)
  
  
  
  # otherwise, we are reading from a video file
  
  else:
  
      camera = cv2.VideoCapture(args["video"])
  
  
  
  # initialize the first frame in the video stream
  
  firstFrame = None
  
  
  
  # loop over the frames of the video
  
  while True:
  
      # grab the current frame and initialize the occupied/unoccupied
  
      # text
  
      (grabbed, frame) = camera.read()
  
      text = "Unoccupied"
  
  
  
      # if the frame could not be grabbed, then we have reached the end
  
      # of the video
  
      if not grabbed:
  
          break
  
  
  
      # resize the frame, convert it to grayscale, and blur it
  
      frame = imutils.resize(frame, width=500)
  
      gray = cv2.cvtColor(frame, cv2.COLOR_BGR2GRAY)
  
      gray = cv2.GaussianBlur(gray, (21, 21), 0)
  
  
  
      # if the first frame is None, initialize it
  
      if firstFrame is None:
  
          firstFrame = gray
  
          continue
  
  
  
      # compute the absolute difference between the current frame and
  
      # first frame
  
      frameDelta = cv2.absdiff(firstFrame, gray)
  
      thresh = cv2.threshold(frameDelta, 25, 255, cv2.THRESH_BINARY)[1]
  
  
  
      # dilate the thresholded image to fill in holes, then find contours
  
      # on thresholded image
  
      thresh = cv2.dilate(thresh, None, iterations=2)
  
      (_, cnts, _) = cv2.findContours(thresh.copy(), cv2.RETR_EXTERNAL, cv2.CHAIN_APPROX_SIMPLE)
  
  
  
      # loop over the contours
  
      for c in cnts:
  
          # if the contour is too small, ignore it
  
          if cv2.contourArea(c) < args["min_area"]:
  
              continue
  
  
  
          # compute the bounding box for the contour, draw it on the frame,
  
          # and update the text
  
          (x, y, w, h) = cv2.boundingRect(c)
  
          cv2.rectangle(frame, (x, y), (x + w, y + h), (0, 255, 0), 2)
  
          text = "Occupied"
  
  
  
      # draw the text and timestamp on the frame
  
      cv2.putText(frame, "Room Status: {}".format(text), (10, 20),
  
          cv2.FONT_HERSHEY_SIMPLEX, 0.5, (0, 0, 255), 2)
  
      cv2.putText(frame, datetime.datetime.now().strftime("%A %d %B %Y %I:%M:%S%p"),
  
          (10, frame.shape[0] - 10), cv2.FONT_HERSHEY_SIMPLEX, 0.35, (0, 0, 255), 1)
  
  
  
      # show the frame and record if the user presses a key
  
      cv2.imshow("Security Feed", frame)
  
      cv2.imshow("Thresh", thresh)
  
      cv2.imshow("Frame Delta", frameDelta)
  
      key = cv2.waitKey(1) & 0xFF
  
  
  
      # if the `q` key is pressed, break from the lop
  
      if key == ord("q"):
  
          break
  
  
  
  # cleanup the camera and close any open windows
  
  camera.release()
  
  cv2.destroyAllWindows()

• Convert ffmpeg frame into array of YUV pixels in C

  9 juin 2016, par loneraver

  I’m using the ffmpeg C libraries and trying to convert an AVFrame into a 2d array of pixels with YUV* components for analysis. I figured out how to convert the Y component for each pixel. :

  uint8_t y_val = pFrame->data[0][pFrame->linesize[0] * y + x]; 

  Since all frames have a Y component this is easy. However most digital video do not have a 4:4:4 chroma subsampling, so getting the UV components is stumping me.

  I’m using straight C for this project. No C++. An ideas ?

  *Note : Yes, I know it’s technically YCbCr and not YUV.

  Edit :

  I’m rather new to C so it might not be the prettiest code out there.

  When I try :

  VisYUVFrame *VisCreateYUVFrame(const AVFrame *pFrame){
  
      VisYUVFrame *tmp = (VisYUVFrame*)malloc(sizeof(VisYUVFrame));
  
      if(tmp == NULL){ return NULL;}
  
      tmp->height = pFrame->height;
  
      tmp->width = pFrame->width;
  
  
  
      tmp->data = (PixelYUV***)malloc(sizeof(PixelYUV**) * pFrame->height);
  
      if(tmp->data == NULL) { return NULL;};
  
  
  
      for(int y = 0; y < pFrame->height; y++){
  
          tmp->data[y] = (PixelYUV**)malloc(sizeof(PixelYUV*) * pFrame->width);
  
          if(tmp->data[y] == NULL) { return NULL;}
  
  
  
          for(int x = 0; x < pFrame->width; x++){
  
              tmp->data[y][x] = (PixelYUV*)malloc(sizeof(PixelYUV*));
  
              if(tmp->data[y][x] == NULL){ return NULL;};
  
              tmp->data[y][x]->Y = pFrame->data[0][pFrame->linesize[0] * y + x];
  
              tmp->data[y][x]->U = pFrame->data[1][pFrame->linesize[1] * y + x];
  
              tmp->data[y][x]->V = pFrame->data[2][pFrame->linesize[2] * y + x];
  
  
  
          }
  
      }
  
  
  
      return tmp;

  Luma works but when I run Valgrind, I get

  0x26
  1
  InvalidRead
  Invalid read of size 1

  0x100003699
  /Users/hborcher/Library/Caches/CLion2016.2/cmake/generated/borcherscope-8e83e7dd/8e83e7dd/Debug/VisCreator2
  VisCreateYUVFrame
  /Users/hborcher/ClionProjects/borcherscope/lib
  visualization.c
  145

  0x100006B5B
  /Users/hborcher/Library/Caches/CLion2016.2/cmake/generated/borcherscope-8e83e7dd/8e83e7dd/Debug/VisCreator2
  render
  /Users/hborcher/ClionProjects/borcherscope/lib/decoder
  simpleDecoder2.c
  253

  0x100002D24
  /Users/hborcher/Library/Caches/CLion2016.2/cmake/generated/borcherscope-8e83e7dd/8e83e7dd/Debug/VisCreator2
  main
  /Users/hborcher/ClionProjects/borcherscope/src
  createvisual2.c
  93

  Address 0x10e9f91ef is 0 bytes after a block of size 92,207 alloc’d

  0x100013EEA
  /usr/local/Cellar/valgrind/3.11.0/lib/valgrind/vgpreload_memcheck-amd64-darwin.so
  malloc_zone_memalign

  0x1084B5416
  /usr/lib/system/libsystem_malloc.dylib
  posix_memalign

  0x10135D317
  /usr/local/Cellar/ffmpeg/3.0.2/lib/libavutil.55.17.103.dylib
  av_malloc

  0x27
  1
  InvalidRead
  Invalid read of size 1

  0x1000036BA
  /Users/hborcher/Library/Caches/CLion2016.2/cmake/generated/borcherscope-8e83e7dd/8e83e7dd/Debug/VisCreator2
  VisCreateYUVFrame
  /Users/hborcher/ClionProjects/borcherscope/lib
  visualization.c
  147

  0x100006B5B
  /Users/hborcher/Library/Caches/CLion2016.2/cmake/generated/borcherscope-8e83e7dd/8e83e7dd/Debug/VisCreator2
  render
  /Users/hborcher/ClionProjects/borcherscope/lib/decoder
  simpleDecoder2.c
  253

  0x100002D24
  /Users/hborcher/Library/Caches/CLion2016.2/cmake/generated/borcherscope-8e83e7dd/8e83e7dd/Debug/VisCreator2
  main
  /Users/hborcher/ClionProjects/borcherscope/src
  createvisual2.c
  93

  Address 0x10e9f91ef is 0 bytes after a block of size 92,207 alloc’d

  0x100013EEA
  /usr/local/Cellar/valgrind/3.11.0/lib/valgrind/vgpreload_memcheck-amd64-darwin.so
  malloc_zone_memalign

  0x1084B5416
  /usr/lib/system/libsystem_malloc.dylib
  posix_memalign

  0x10135D317
  /usr/local/Cellar/ffmpeg/3.0.2/lib/libavutil.55.17.103.dylib
  av_malloc

• Is there a way to use ffmpeg audio filters to automatically synchronize 2 streams with similar content

  29 mai 2015, par user3741412

  I have a situation where I have a video capture of HD content via HDMI with audio from a sound board that goes through a impedance drop into a microphone input of a camcorder. That same signal is split at line level to a ’line in’ jack on the same computer that is capturing the HDMI. Alternatively I can capture the audio via USB from the soundboard which is probably the best plan, but carries with it the same issue.

  The point is that the line in or usb capture will be much higher quality than the one on HDMI because the line out -> impedance change -> mic in path generates inferior quality in that simply brushing the mic jack on the camera while trying to change the zoom (close proximity) can cause noise on the recording.

  So I can do this today :

  • Take the good sound and the camera captured sound and load each into
    audacity and pretty quickly use the timeshift toot to perfectly fit
    the good audio to the questionable audio from the HDMI capture and
    cut the good audio to the exact size of the video. Then I can use
    ffmpeg or other video editing software to replace the questionable
    audio with the better audio.

  But while somewhat quick and easy, it always carries with it a bit of human error and time. I’d like to automate this if possible as this process is repeated at least weekly throughout the year.

  Does anyone have a suggestion if any of these ideas have merit or could suggest another approach ?

  1. I suspect but have yet to confirm that the system timestamp of the start time may be recorded in both audio captured with something like Audacity, or the USB capture tool from the sound board as well as the HDMI mpeg-2 video. I tried ffprobe on a couple audacity captured .wav files but didn’t see anything in the results about such a time code, but perhaps other audio formats or other probing tools may include this info. Can anyone advise if this is common with any particular capture tools or file formats ?

     • if so, I think I could get best results by extracting this information and then using simple adelay and atrim filters in ffmpeg to sync reliably directly from the two sources in one ffmpeg call. This is all theoretical for me right now— I’ve never tried either of these filters yet— just trying to optimize against blind alleys by asking for advice up front.

  2. If such timestamps are not embedded, possibly I can use the file system timestamp for the same idea expressed in 1a, but I suspect the file open of the two capture tools may have different inherant delays. Possibly these delays will be found to be nearly constant and the approach can work with a built-in constant anticipation delay but sounds messy and less reliable than idea 1. Still, I’d take it, if it turns out reasonably reliable

  3. Are there any ffmpeg or general digital audio experts out there that know of particular filters that can be employed on the actual data to look for similarities like normalizing the peak amplitudes or normalizing the amplification of the two to some RMS value and then stepping through a short 10 second snippet of audio, moving one time stream .01s left against the other repeatedly and subtracting the two and looking for a minimum ? Sounds like it could take a while, but if it could do this in less than a minute and be reliable, I suspect it could work. But I have only rudimentary knowledge of audio streams and perhaps what I suggest is just not plausible— but since each stream starts with the same source I think there should be a chance. I am just way out of my depth as to how to go down this road, so if someone out there knows such magic or can throw me some names of filters and example calls, I can explore if I can make it work.

  4. any hardware level suggestions to take a line level output down to a mic level input and not have the problems I am seeing using a simple in-line impedance drop module, so that I can simply rely on the audio from the HDMI ?

  Thanks in advance for any pointers or suggestinons !