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• How to take frames in real-time in a RTSP streaming ?

  30 juin 2018, par guijob

  I’m trying to grab frames with no delays using javacv and I’m kind of confusing how to do it and how javacv and other stuff properly work under the hoods.

  In my example, I have a RTSP streaming running with following configurations :

  Codec: H.264
  
  Frame Size: 1280x720
  
  Maximum Frame Rate: 60 fps

  In order to make it happen, I’ve made a thread like following :

  public class TakeFrameFromStreamingThread implements Runnable {
  
    private CircularFifoQueue queue;
  
    private Camera camera;
  
    private FFmpegFrameGrabber grabber = null;
  
  
  
    public TakeFrameFromStreamingThread(CircularFifoQueue queue, Camera camera) {
  
      try {
  
        this.queue = queue;
  
        this.camera = camera;
  
        this.initGrabber(camera);
  
      } catch (Exception e) {
  
        e.printStackTrace();
  
      }
  
    }
  
  
  
    @Override
  
    public void run() {
  
      try {
  
        while (true) {
  
          if (grabber == null) {
  
            initGrabber(camera); // connect
  
      }
  
  
  
      Frame frame = null;
  
      frame = grabber.grabImage();
  
  
  
      if (frame != null) {
  
        this.queue.add(frame);
  
      } else { // when frame == null then connection has been lost
  
        initGrabber(camera); // reconnect
  
      }
  
        }
  
      } catch (Exception e) {
  
        e.printStackTrace();
  
      }
  
    }
  
  
  
    private void initGrabber(Camera camera) throws Exception {
  
      grabber = new FFmpegFrameGrabber(camera.getURL()); // rtsp url
  
      grabber.setVideoCodec(avcodec.AV_CODEC_ID_H264);
  
      grabber.setOption("rtsp_transport", "tcp");
  
      grabber.setFrameRate(60);
  
      grabber.setImageWidth(camera.getResolution().getWidth());
  
      grabber.setImageHeight(camera.getResolution().getHeight());
  
      grabber.start();
  
    }
  
  }

  And it seems to work. Anytime I need a frame I pool this queue from my main thread.

  I’ve ended up with this solution solving another issue. I was getting stuck why does calling grabImage() every time I need a frame has returned just next frame instead of a real-time frame from streaming.

  By this solution, I’m guessing there is a buffer which javacv (or ffmpeg idk) fills with frames and then grabImage() just get a frame from this buffer. So it’s my first question :

  1) Is that right ? Does ffmpeg relies on a buffer to store frames and then grab() just get it from there ?

  Well, if that is a truth, then this buffer must be filled at some rate and, of course, if this rate is greater than my grabImage() calls rate, eventually I’ll lose my real-time feature and soon I’ll be even losing frames once buffer gets completely filled.

  In this scenario, my grabImage() takes about 50 ms, which gives me 20 fps rate getting frames from this buffer. Hence, I need to make sure ffmpeg is receiving frames at most 20 fps. So here’s my second question :

  2) How to know and change ffmpeg buffer rate ? I’m guessing it’s getting filled at a same rate of streaming (60 fps) or from property grabber.setFrameRate(). At all, I’m not sure if I should use grabber setters with same values from source streaming.

• avcodec/ccaption_dec : Make real-time latency configurable

  19 juin 2021, par Pavel Koshevoy

  avcodec/ccaption_dec : Make real-time latency configurable
  Un-hardcode the 200ms minimum latency between emitting subtitle events
  
  so that those that wish to receive a subtitle event for every screen
  
  change could do so.
  The problem with delaying realtime output by any amount is that it is
  
  unknown when the next byte pair that would trigger output will happen.
  
  It may be within 200ms, or it may be several seconds later — that's
  
  not realtime at all.
  

  • [DH] libavcodec/ccaption_dec.c
  • [DH] libavcodec/version.h

• Revision cde6b50cb1 : Merge "Use fast HEX search in real time mode"

  20 février 2014, par Yunqing Wang

  Changed Paths :
   Modify /vp9/encoder/vp9_onyx_if.c

  
   Modify /vp9/encoder/vp9_onyx_int.h

  
   Modify /vp9/encoder/vp9_rdopt.c

  
  
  Merge "Use fast HEX search in real time mode"