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• How can I open a rtsp stream with ffplay and feed the frames to opencv ?

  27 novembre 2020, par Scion11

  I'm working on a CV project streaming from an IP camera. I happened to find it is faster to stream with ffplay than with opencv directly. This is because opencv does not provide a flush()-like function that clears the buffer before retrieving a frame. In that case, opencv always takes the first frame instead of the last frame for use.

  


  I'm just wondering if there's a way to use ffplay (or ffmpeg) as backend to feed the latest frame to opencv.

  


  Comparing the following code, ffplay is much faster than opencv in streaming :

  


  import cv2
import subprocess


# OpenCV lags for ~1s
def cv2rtsp(rtspurl):
    cap = cv2.VideoCapture(rtspurl)
    ret, img = cap.read()

    while True:
        cap.grab()
        ret, img = cap.retrieve()
        if ret:
            cv2.imshow('video output', img)
        if cv2.waitKey(1) == ord('q'):
            raise StopIteration


# FFmpeg lags for ~500ms
def ffmpeg_rtsp(rtspurl):
    command = [
        'ffplay', '-fflags', 'nobuffer', '-flags', 'low_delay', '-framedrop', '-strict', 'experimental', rtspurl
    ]

    subprocess.call(command)


if __name__ == '__main__':
    rtsp = "rtsp://admin:my123456@192.168.0.53:554/h264/ch1/sub/av_stream"
    cv2rtsp(rtspurl=rtsp)
    ffmpeg_rtsp(rtspurl=rtsp)


  


• What open source software would be best for reading in raw data from an SDR / USRP and decoding ATSC1.0 video and playing it ?

  18 août 2023, par railsnoob

  I've had luck with GNU Radio for ATSC1.0 decode from USRP data and sending the mpeg transport stream to VLC to be played but eventually I would like to have other DTV standards decoded.

  


  I started looking into packages with full DTV support and saw that VLC has TV tuner control/access, but if I have a USRP I'm not sure I could configure VLC to control that, or if I'd even want it to. But since it can go from tuner control to video playback there must be a command/configuration which just has it read from a raw data file that I captured from the USRP, right ?

  


  Does anyone know how to go from raw captured ATSC channel to MPEG transport stream on VLC, FFMPEG, or any other software packages ?

  


• ffmpeg decoding MP4 to Open GL texture black screen

  5 septembre 2019, par Dakiaiu

  I decoded a MP4 video and want to display the AVFrame via glTexImage2D and glTexSubImage2D but all I get is a blank GL Window.

  I’ve tried looking at the various examples in the ffmpeg github examples tree. https://github.com/FFmpeg/FFmpeg/tree/master/doc/examples and different posts from the past and recently on this site learning slowly from them but I could not find anything I am doing wrong.

  while(av_read_frame(format_context,packet) >= 0){
  
  
  
          if(packet->stream_index == video_stream_index){
  
  
  
              av_frame = decode(codec_context,av_frame,packet);
  
  
  
              sws_context = sws_getContext(codec_context->width,codec_context->height,codec_context->pix_fmt,codec_context->width,codec_context->height,
  
                      AV_PIX_FMT_RGB24, SWS_BICUBIC,nullptr,nullptr,nullptr);
  
  
  
              sws_scale(sws_context,
  
                      av_frame->data,
  
                      av_frame->linesize,
  
                      0,
  
                      codec_context->height,
  
                      gl_frame->data,
  
                      gl_frame->linesize);
  
  
  
              sws_freeContext(sws_context);
  
  
  
              if(first_use == true) {
  
  
  
                  glTexImage2D(GL_TEXTURE_2D,
  
                               0,
  
                               GL_RGB,
  
                               codec_context->width,
  
                               codec_context->height,
  
                               0,
  
                               GL_RGB,
  
                               GL_UNSIGNED_BYTE,
  
                               gl_frame->data[0]);
  
  
  
                  first_use = false;
  
  
  
              }else{
  
  
  
                  glTexSubImage2D(GL_TEXTURE_2D,
  
                          0,
  
                          0,
  
                          0,
  
                          codec_context->width,
  
                          codec_context->height,
  
                          GL_RGB,
  
                          GL_UNSIGNED_BYTE,
  
                          gl_frame->data[0]);
  
  
  
              }
  
  
  
          }
  
  
  
  
  
      }
  
  
  
  
  
      while( glfwGetKey(window, GLFW_KEY_ESCAPE ) != GLFW_PRESS &&
  
             glfwWindowShouldClose(window) == 0 );
  
  
  
  }

  The frames decode successfully but I cannot see anything. It has to be something with the above gl code that I have done wrong. I can show the ffmpeg code above if necessary.