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• Concatenating with ffmpeg - audio out of sync after 2 or 3 files

  1er août 2015, par eCronik

  I have recorded some hour long .flv files I want to glue together. For that, I am using the concat script from https://trac.ffmpeg.org/wiki/Concatenate

  (on the page, at the bottom) with the following tweaks :

  EXTRA_OPTIONS='-c:v libx264 -preset slow -profile:v main -b:v 2175k -minrate 2175k -maxrate 2175k -bufsize 2175k -g 80 -c:a aac -strict -2 -b:a 192k'

  and at the bottom :

  ffmpeg -f u16le -acodec pcm_s16le -ac 2 -ar 44100 -re -i $TMP/mcs_a_all \
  
     -f yuv4mpegpipe -vcodec rawvideo -re -i $TMP/mcs_v_all -loop 1 -i /path/to/overlay.png \
  
     -filter_complex "[1:v][2:v]overlay=shortest=1[v]" -map "[v]" -map 0:a $EXTRA_OPTIONS \
  
     -f flv $last

  The first file, when started, is always 100% sync’ed. Files are randomized, so it’s not always the same one. When it reaches the second or third file, the audio (or video ?) gets more and more out of sync. I’ve tried

  '-vsync 0' as well as '-vsync 0 -copyts'

  but nothing helped so far. The files are all recorded with a sample rate of 44.1kHz - audio bitrate and video bitrate might vary a bit between them, but were always constant. To record them, I have used the following :

  -c:v libx264 -preset slow -profile:v main -b:v 2175k -minrate 2175k -maxrate 2175k -bufsize 2175k -r 40 -g 80 -keyint_min 40 -x264opts "keyint=80:min-keyint=80:no-scenecut" -c:a aac -strict -2 -b:a 192k -f flv rtmp://address \-c copy -f flv rtmp://address;

  The ’-keyint_min 40 -x264opts "keyint=80:min-keyint=80:no-scenecut"’ was added at a later point - so some files are recorded with it, some others were without.

  Does anybody has an idea what else I could try to fix it ? As the first file is always sync’ed, I guess the problem is not that the files were recorded wrong.

  Thanks a bunch,
  eC

• Read h264 stream from an IP camera

  13 juillet 2015, par João Neves

  Currently, I am trying to use opencv to read a video from my Canon VB-H710F camera.

  For this purpose I tried two different solutions :

  SOLUTION 1 : Read the stream from rtsp address

   VideoCapture cam ("rtsp://root:camera@10.0.4.127/stream/profile1=u");
  
  
  
   while(true)
  
    cam >> frame;

  In this case I am using opencv to directly read from a stream encoded with in H264 (profile1), however this yields the same problem reported here http://answers.opencv.org/question/34012/ip-camera-h264-error-while-decoding/
  As suggested in the previous question, I tried to disable FFMPEG support in opencv installation, which solved the h264 decoding errors but raised other problem.
  When accessing the stream with opencv, supported by gstreame, there is always a large delay associated.
  With this solution I achieve 15 FPS but I have a delay of 5 seconds, which is not acceptable considering that I need a real time application.

  SOLUTION 2 : Read the frames from http address
  while(true)
  
  startTime=System.currentTimeMillis() ;

          URL url = new URL("h t t p://[IP]/-wvhttp-01-/image.cgi");
  
          URLConnection con = url.openConnection();
  
          BufferedImage image = ImageIO.read(con.getInputStream());   
  
          showImage(image);
  
          estimatedTime=System.currentTimeMillis()-startTime;
  
          System.out.println(estimatedTime);
  
          Thread.sleep(5);
  
  }

  This strategy simply grabs the frame from the url that the camera provides. The code is in Java but the results are the same in C++ with the curl library.
  This solution avoids the delay of the first solution however it takes little more than 100 ms to grab each frame, which means that I can only achieve on average 10 FPS.

  I would like to know how can I read the video using c++ or another library developed in c++ ?

• How to retransmit RTSP stream to media server Qt C++

  10 juillet 2021, par vishal dharankar

  I have an application where I receive a RTSP stream on a local IP address . This stream I want to retransmit to a media server which runs on public IP.

  


  Is it possible to forward such stream to next server without deciding and encoding this saving computations ?

  


  Can we use Gstreamer or any other similar library for this ?

  


  Sorry for not attaching any code since I am not sure where to start and what can be a specific library for this .

  


  Any pointers are helpful