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• OpenCV VideoCapture closes with videos from GoPro

  10 février 2021, par Michael

  I have a videofile from a GoPro device and I simply work with it from a VideoCapture like this :

  



  cap = cv2.VideoCapture(path)
        index = 0
        start = time.time()

        while cap.isOpened():
            ret, frame = cap.read()
            if not ret:
                break
            # do something here
        end = time.time()


  



  It is very weird, but I can operate with any files except ones, captured at the GoPro. Stream just closes at some point because ret value becomes False and frame becomes None. No exceptions or anything else.

  



  Googling helped me to find this question. I have deleted audio streams from file with ffmpeg tool and then everything works just fine. So why it is like so ? Pleas help !

  



  I am using Python 3.6.4 x64, Windows 10 (however at Linux same) and precompiled binaries for OpenCV from this resource.

  


• How to write a video stream containing B-frame and no DTS to a MP4 container ?

  14 février 2020, par SteveH

  I want to save a h264 video stream received from a RTSP source to a MP4 container.
  Not like other questions asked on SO, here the challenges I face are :

  • The stream contains B frames.

  • The stream has only PTS given by the RTP/RTCP.

  Here is the code I did

  //  ffmpeg
  
      pkt->data = ..;
  
      pkt->size = ..;
  
      pkt->flags = bKeyFrame? AV_PKT_FLAG_KEY : 0;    
  
      pkt->dts = AV_NOPTS_VALUE;
  
      pkt->pts = PTS;
  
  
  
      // PTS is based on epoch microseconds so I ignored re-scaling.
  
      //av_packet_rescale_ts(pkt, { 1, AV_TIME_BASE }, muxTimebase);
  
  
  
      auto ret = av_interleaved_write_frame(m_pAVFormatCtx, pkt);

  I received a lot of error messages like this :
  "Application provided invalid, non monotonically increasing dts to muxer ...".

  Result : the mp4 file is playable via VLC but the FPS is just a half of the original FPS and the video duration is incorrect (VLC shows a weird number).

  So how do I set correct DTS and PTS before sending to the container ?

  Update :
  I have tried some changes, though not successfully yet, I found that the reason of the frame rate drop is due to the muxer discards frames having incorrect DTS.
  Additionally, if I set start of PTS and DTS value too big, some players like VLC has to delay some time before showing video.

• colors messed up (distorted) when making a gif from png files using ffmpeg

  13 novembre 2019, par wxyz

  I have a sequence of png images : image_00.png, image_01.png, image_02.png, etc. I want to convert them to a gif, so I tried the command

  ffmpeg -i image_%02d.png video.gif

  Unfortunately, the resulting gif has distorted colors. More specifically, it added a weird sort of yellow haze around some objects in the video.

  I also tried using the command above with all possible pixel format options (which I determined using the command ffmpeg -h encoder=gif) : rgb8, bgr8, rgb4_byte, bgr4_byte, gray, pal8. For example ffmpeg -i image_%02d.png -pix_fmt rgb8 video.gif. Unfortunately, all of the resulting gifs had some sort of color distortion.

  I also observed that this distortion does not occur if I convert the images to mp4 instead of gif. However, if I try converting that mp4 to a gif, I end up with the distortion again.

  How can I produce this gif without color distortion ?