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• OpenCV no longer opens video files VideoCapture

  15 février 2018, par gruffmeister

  I have a problem seemingly caused by OpenCV 3.xx - the problem does not manifest in OpenCV 2.xx

  The issue is reading video files. I’ve set my code up as follows :

  >#include 
  
  >#include 
  
  >#include 
  
  >#include 
  
  >#include 
  
  
  
  >int main()
  
  
  
  >    cv::VideoCapture cap;
  
  >    cv::Mat frame;
  
  >    if(!cap.open("Myfile.avi"))
  
  >        std::cout << "Open failed" << std::endl;
  
  >    else
  
  >        cap.read(frame);
  
  >
  
  >    cv::imshow("Frame", frame);
  
  >    cv::waitKey(5000);
  
  >    return 0;

  Now the problem is when the code gets to "cap.read(frame)" I get a "vector subscript is out of range" error with OpenCV 3.40 and this does not happen with my build of OpenCV 2.4.9. The format of the file is in avi, its not some weird codec, and clearly it works in previous versions of OpenCV.

  I’ve tried other OpenCV 3.xx builds and I get the same or similar problems with simply reading a file in.

  My question is twofold :
  How do I get OpenCV 3.xx to work with reading video files (or do I need to regress to 2.xx ?)

  Why has the major revision change completely screwed up video file reading ? That doesn’t make any sense for a computer vision API.

  As a guess it will be something to do with the FFMPEG implementation because various searches have turned up other people having issues with this.

  Any help is much appreciated.

  Thanks

• when concatenating video segments ffmpeg shows error : "Media type mismatch between the parsed_overlay_20"

  27 janvier 2018, par user2642511

  773/5000
  I’m trying to apply a scaling and chromakey effect to different segments of a video and then combine those segments again into one.

  To improve the time and performance I have developed a program that creates all the filters in a single command.

  The plan is simple, I have a video * .mov recorded with a green screen and a background * .jpg,

  1. I first prepare a couple of backgrounds with blur effect from the JPG image
  2. I then apply chromakey to make the green part of the video transparent
  3. I trim the video to which I applied the chromakey in several time segments and to each segment I applied a scale and crop and I overlay it to one of the backgrounds prepared in step 1
  4. Concatenate all segments already processed.

  When I execute the resulting command it gives me the error

  the command is this :

  ffmpeg -i "C:\ffmpeg\pruebas\FFBlue_ProjectsFiles\chroma\green1.mov" -i C:\ffmpeg\pruebas\FFBlue_ProjectsFiles\fondos\sc.jpg -filter_complex " [1:v]scale=iw*3:-1,crop=w=iw/3:h=ih/3:y=(ih-oh)/3:x=((iw-ow)/2)+(ow/2-ow/3),boxblur=7:2[fondo_3IZQ] ; [1:v]scale=iw*4:-1,crop=w=iw/4:h=ih/4:y=(ih-oh)/3:x=(in_w-out_w)/2,boxblur=6:2[fondo_4CEN] ; [1:v]scale=iw*5:-1,crop=w=iw/5:h=ih/5:y=(ih-oh)/3:x=((iw-ow)/2)+(ow/2-ow/3),boxblur=5:2[fondo_5IZQ]  ; [0]chromakey=color=#83BD46:similarity = 0.1 : blend = 0.05,selectivecolor=reds=0 0 0 -1:yellows=0 0.1 0 -0.5:greens=0 0 -1 0:whites=0 0 0 -0.7 [vid]  ;  [vid] trim=start=0:duration=0,setpts=PTS-STARTPTS,scale=iw*4:-1,crop=w=iw/4:h=ih/4:y=(ih-oh)/3:x=((iw-ow)/2)+(ow/2-ow/3)[vid_0] ; [fondo_4CEN][vid_0]overlay[toma_0] ; [vid] trim=start=0:duration=3.41933,setpts=PTS-STARTPTS,scale=iw*3:-1,crop=w=iw/3:h=ih/3:y=(ih-oh)/3:x=(in_w-out_w)/2[vid_1] ; [fondo_3IZQ][vid_1]overlay[toma_1] ; [vid] trim=start=3.41932988166809:duration=2.85067,setpts=PTS-STARTPTS,scale=iw*5:-1,crop=w=iw/5:h=ih/5:y=(ih-oh)/3:x=(in_w-out_w)/2[vid_2] ; [fondo_5IZQ][vid_2]overlay[toma_2]  ; [toma_0] [toma_1] [toma_2] concat=n=3:v=1:a=1:unsafe=1 [v_concatenado][a_concatenado]" -map [v_concatenado]  -map [a_concatenado] "C:\ffmpeg\pruebas\FFBlue_ProjectsFiles\chroma\green1_FINAL.mov"

  when I execute it ffmpeg says :

  [Parsed_overlay_20 @ 0000000000404100] Media type mismatch between the 'Parsed_o
  
  verlay_20' filter output pad 0 (video) and the 'Parsed_concat_26' filter input p
  
  ad 1 (audio)
  
  [AVFilterGraph @ 0000000003527a00] Cannot create the link overlay:0 -> concat:1
  
  Error initializing complex filters.
  
  Invalid argument

• Delay in setting RTP packets using FFMpeg [on hold]

  25 janvier 2018, par rurtle

  So, I’m trying to stream video using FFMpeg from my embedded box to VLC media player on a PC. While doing so, I’m noticing lots of video freezing. VLC is reporting -
  pulse audio output debug: underflow. I’m using the following command to start streaming with FFMpeg -

  ./ffmpeg -stream_loop -1 -re -i generic.ts -acodec copy -vcodec copy -f rtp_mpegts rtp://239.224.0.1:5000?pkt_size=200

  When I set the pkt_size to 400, streaming performance is a lot worse. FFMpeg version : 3.4.

  Accidentally, I found that if I start ping from PC to my box, the performance improves dramatically. I am using Linux on the dev box.

  So, my questions are -

  1. Is there any command line option that I can use on FFMpeg to improve streaming ?
  2. How ping can affect the streaming performance ?

  Thanks in advance !