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• How to start and stop saving video frames according to a trigger with OpenCV VideoWriter

  11 août 2021, par Jacob nighFor

  I am building an app that records frames from IP camera through RTSP.

  



  My engine is in charge to save a video in mp4 with Opencv VideoWriter working well.
What I am looking for is to create a startRecord and a stopRecord class method that will respectively start and stop recording according to a trigger (it could be an argument that I pass to the thread).
Is anyone know what the best way to do that kind of stuff ?

  



  Here is my class :

  



  from threading import Thread
import cv2
import time
import multiprocessing
import threading
class RTSPVideoWriterObject(object):
    def __init__(self, src=0):
        # Create a VideoCapture object
        self.capture = cv2.VideoCapture(src)

        # Start the thread to read frames from the video stream
        self.thread = Thread(target=self.update, args=())
        self.thread.daemon = True
        self.thread.start()

    def update(self):
        # Read the next frame from the stream in a different thread
        while True:
            if self.capture.isOpened():
                (self.status, self.frame) = self.capture.read()

    def endRecord(self):
        self.capture.release()
        self.output_video.release()
        exit(1)

    def startRecord(self,endRec):

        self.frame_width = int(self.capture.get(3))
        self.frame_height = int(self.capture.get(4))
        self.codec = cv2.VideoWriter_fourcc(*'mp4v')
        self.output_video = cv2.VideoWriter('fileOutput.mp4', self.codec, 30, (self.frame_width, self.frame_height))
        while True:          
            try:
                self.output_video.write(self.frame)
                if endRec:
                    self.endRecord()
            except AttributeError:
                pass




if __name__ == '__main__':

    rtsp_stream_link = 'rtsp://foo:192.5545....'
    video_stream_widget = RTSPVideoWriterObject(rtsp_stream_link)

    stop_threads = False
    t1 = threading.Thread(target = video_stream_widget.startRecord, args =[stop_threads]) 
    t1.start() 
    time.sleep(15)
    stop_threads = True



  



  As you can see in the main I reading frames and store them in a separate thread. Then I am starting to record (record method is with an infinite loop so blocking) and then after 15 sec, I am trying to pass a 'stop_record' argument to stop recording properly.

  



  A part of the code comes from Storing RTSP stream as video file with OpenCV VideoWriter

  



  Is someone have an idea ?
I read a lot that OpenCV can be very tricky for multithreading

  



  N.

  


• UDP Receiver needs to start before udp sender

  11 janvier 2020, par user27443

  I’m trying to send video from a raspberry pi 0w with camera running Raspian Buster to a machine running Ubuntu 18.04. I’m using ffmpeg to encode to h264 using hardware on the raspi end, and then sending the data with gst-launch-1.0 over UDP. The issue is that if I start the raspi stream, and then start the receiver, the receiver never connects. If I start the receiver and then start the raspi stream, then they connect perfectly.

  Raspi encode and send command :

  ffmpeg -f video4linux2 -framerate 30 -video_size 1280x720 -i /dev/video0 -c:v h264_omx -b:v 2000k -f avi pipe:1 | gst-launch-1.0 --gst-debug=3 fdsrc ! udpsink host=192.168.1.142 port=8090

  Receive and decode and display command :

  gst-launch-1.0 udpsrc port=8090 ! queue ! h264parse ! avdec_h264 ! xvimagesink sync=false

  I’ve looked at the udpsink and udpsrc properties and tried messing around with buffer-size, blocksize, and sync with no luck. I’ve also tried using ffmpeg from python to see if the issue was on the receiver side, with the exact same problem.

  import cv2
  
  
  
  cap = cv2.VideoCapture('udp://127.0.0.1:8090',cv2.CAP_FFMPEG)
  
  if not cap.isOpened():
  
      print('VideoCapture not opened')
  
      exit(-1)
  
  
  
  while True:
  
      ret, frame = cap.read()
  
  
  
      if not ret:
  
          print('frame empty')
  
          break
  
  
  
      cv2.imshow('image', frame)
  
  
  
      if cv2.waitKey(1)&0XFF == ord('q'):
  
          break
  
  
  
  cap.release()
  
  cv2.destroyAllWindows()

  In the end, I might just write a small protocol that toggles the sender if no packets are getting through, but I was hoping that UDP would handle the connection better.

  This question seemed simliar : UDP : Client started before Server but didn’t resolve my issue since I don’t have any blocking ability with gstreamer/ffmpeg.

• Set correct start time of ts-file using ffmpeg

  9 octobre 2020, par Daniel

  I am splitting up a video into multiple 10 second ts-parts (mpeg-ts format) using ffmpeg on windows.

  



  To create the 2nd part (that starts at 10 seconds into the video and ends at 20 seconds into the video) :

  



  ffmpeg -i sample.avi -ss 00:00:10 -to 00:00:20 -vcodec libx264 -acodec aac -vf scale=426:-1 out1.ts


  



  But when i check the file using ffprobe it says :

  



  Duration: 00:00:10.02, start: 1.458667, bitrate: 359 kb/s


  



  So the duration is ok but the start time is incorrect. Is it anyway i can use ffmpeg to correct it to 00:00:20 ?
The best solution would of course to be able to set the correct start time in my first command where i take out the 10 second part but i would also be ok with running a 2nd command to fix the time.

  



  Is this possible ? Cant find any documentation and all examples i found are not for my exact problem and don't seem to work then i play around with them.

  



  Full output from ffprobe :

  



  ffprobe.exe out1.ts
ffprobe version git-2020-02-06-343ccfc Copyright (c) 2007-2020 the FFmpeg developers
  built with gcc 9.2.1 (GCC) 20200122
  configuration: --enable-gpl --enable-version3 --enable-sdl2 --enable-fontconfig --enable-gnutls --enable-iconv --enable-libass --enable-libdav1d --enable-libbluray --enable-libfreetype --enable-libmp3lame --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-libopenjpeg --enable-libopus --enable-libshine --enable-libsnappy --enable-libsoxr --enable-libtheora --enable-libtwolame --enable-libvpx --enable-libwavpack --enable-libwebp --enable-libx264 --enable-libx265 --enable-libxml2 --enable-libzimg --enable-lzma --enable-zlib --enable-gmp --enable-libvidstab --enable-libvorbis --enable-libvo-amrwbenc --enable-libmysofa --enable-libspeex --enable-libxvid --enable-libaom --enable-libmfx --enable-ffnvcodec --enable-cuvid --enable-d3d11va --enable-nvenc --enable-nvdec --enable-dxva2 --enable-avisynth --enable-libopenmpt --enable-amf
  libavutil      56. 39.100 / 56. 39.100
  libavcodec     58. 68.100 / 58. 68.100
  libavformat    58. 38.100 / 58. 38.100
  libavdevice    58.  9.103 / 58.  9.103
  libavfilter     7. 74.100 /  7. 74.100
  libswscale      5.  6.100 /  5.  6.100
  libswresample   3.  6.100 /  3.  6.100
  libpostproc    55.  6.100 / 55.  6.100
Input #0, mpegts, from 'out1.ts':
  Duration: 00:00:10.02, start: 1.458667, bitrate: 359 kb/s
  Program 1
    Metadata:
      service_name    : Service01
      service_provider: FFmpeg
    Stream #0:0[0x100]: Video: h264 (High) ([27][0][0][0] / 0x001B), yuv420p(progressive), 426x260 [SAR 780:781 DAR 18:11], 25 fps, 25 tbr, 90k tbn, 50 tbc
    Stream #0:1[0x101]: Audio: aac (LC) ([15][0][0][0] / 0x000F), 48000 Hz, stereo, fltp, 131 kb/s