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• Can the outputFile of MediaRecorder be a named pipe ?

  13 avril 2017, par Harrison

  Following
  Android Camera Capture using FFmpeg
  and
  feed raw yuv frame to ffmpeg with timestamp

  I successfully put raw frames of Android phone camera into a named pipe made by mkfifo, and used ffmpeg to process them and generated a video file.

  But the problem is that by ffmpeg, the encoding is very slow, it can only process 3 5 frames per second. The reason I have to use ffmpeg instead of MediaRecorder is that later I need to use ffmpeg to generate HLS segments and m3u8 file.

  So I have to turn to use native encoder like MediaRecorder and try to set its OutputFile to a named pipe following
  How to use unix pipes in Android

  My code likes this,

  private String pipe = "/data/data/com.example/v_pipe1";
  
  ...
  
  mMediaRecorder.setOutputFile(pipe);
  
  ...
  
  mMediaRecorder.start();

  Also I have a ffmpeg thread to use this pipe as the input.

  But when I call mMediaRecorder.start() ; It will throw java.lang.IllegalStateException. I’ve tried to put ffmpeg thread before or after calling mMediaRecorder.start(), but with the same error.

  I have no idea about this now. Could someone tell me how to solve this ?
  Any suggestions are welcome and appreciated. Thanks.

• OpenCV python, reading video frames from ffmpeg pipe

  26 avril 2017, par codefame

  I’m trying to use ffmpeg to pipe a video to opencv frame by frame.

  Structure :

  1. main script calls threaded process to obtain video & pipe video to
     image2pipe
  2. main script calls threaded process to read stdout for
     frame info
  3. main script calls function to continuously check for
     frame data

  Video Capture Function :

  def recordstream(self):
  
      global pipe
  
      # start video capture process
  
      pipe = Popen([VIDEO_CAPTURE_SOURCE + " | ffmpeg -i pipe:0 -pix_fmt bgr24 -r 1 -f image2pipe -"], stdout = PIPE, bufsize=10**8, shell=True)

  This ffmpeg code seems to work just fine when the capture source was tested with a single frame, but it doesn’t work using the video stream.

  Buffer Read Function :

  def rawImage(self):
  
      global pipe, raw_image
  
      raw_image = pipe.stdout.read() # save output for opencv

  I gave this its own thread because it seems to be a blocking function.

  OpenCV Function :

  def checkframe(self):
  
      time.sleep(2)
  
      global raw_image
  
  
  
      while(True):
  
          array = numpy.frombuffer(raw_image, dtype='uint8')
  
          frame = cv2.imdecode(array, 1)
  
  
  
          if frame is None:
  
              print("Image not found")
  
          else:
  
              print("FOUND IMAGE")
  
              cv2.imshow(frame)
  
              if cv2.waitKey(1) & 0xFF == ord('q'):
  
                  break

  This function fails at frame = cv2.imdecode(array, 1) as the array seems to be empty.

  Error :

  !buf.empty() && buf.isContinuous() in function imdecode_

  I see lots of discussion around piping data from OpenCV to ffmpeg, but not much the other way around. What am I missing here ?

  Thanks in advance.

• Pipe PIL images to ffmpeg stdin - Python

  9 mai 2017, par bluesummers

  I’m trying to convert an html5 video to mp4 video and am doing so by screen shooting through PhantomJS over time

  I’m also cropping the images using PIL so eventually my code is roughly :

  while time() < end_time:
  
      screenshot_list.append(phantom.get_screenshot_as_base64())
  
  .
  
  .
  
  for screenshot in screenshot_list:
  
      im = Image.open(BytesIO(base64.b64decode(screenshot)))
  
      im = im.crop((left, top, right, bottom))

  Right now I’m saving to disc all those images and using ffmpeg from saved files :

  os.system('ffmpeg -r {fps} -f image2 -s {width}x{height} -i {screenshots_dir}%04d.png -vf scale={width}:-2 '
  
        '-vcodec libx264 -crf 25 -vb 20M -pix_fmt yuv420p {output}'.format(fps=fps, width=width,
  
                                                                    screenshots_dir=screenshots_dir,
  
                                                                    height=height, output=output))

  But I want instead of using those saved files, to be able to pipe the PIL.Images directy to ffmpeg, how can I do that ?