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• Using ffmpeg, extract small part of .m4a audio file and set extract file duration correctly

  30 août 2015, par Kes

  I have Linux mint 17.1.

  When I use ffmpeg to cut out a section of a 4 hour long .m4a audio file as follows :

  ffmpeg -ss 0:10:00 -i in_file.m4a -vn -c copy -t 0:40:00 out_file.m4a

  the correct position and duration of extract is extracted and the file plays just fine, but the audio duration meta-tag in the playback player is incorrectly shown as 4 hours.

  How can I set the actual extract duration so it is correct, in this case 30mins, or even better get ffmpeg to calculate it and set it properly ?

  Thank you

• Wrong frame rate when saving camera feed to a file using FFMPEG

  23 août 2015, par LEM

  I’m trying to save the live feed from an IP camera to a file but the resulting file always plays much faster than the original speed.

  I have tried with the following commands :

  ffmpeg -i http://171.22.3.47/image -vcodec copy -an -t 900 c:\output.mp4
  
  
  
  ffmpeg -i http://171.22.3.47/image -c:v libx264 -an c:\output.mp4

  Does anybody know what I’m missing ? Both commands create the file and I can use Windows Media Player to play them, but they run much faster.

• Video too fast FFmpeg

  22 novembre 2012, par Spamdark

  I am having an issue again with ffmpeg, I'm a newbie with ffmpeg, and I can't find a good tutorial up to date...

  This time, when I play a video with ffmpeg, it plays too fast, ffmpeg is ignoring the FPS, I don't want to handle that with a thread sleep, because the videos have differents FPS's.

  I created a thread, there you can find the loop :

  AVPacket framepacket;
  
  
  
  while(av_read_frame(formatContext,&framepacket)>= 0){
  
      pausecontrol.lock();
  
  
  
      // Is it a video or audio frame¿?
  
      if(framepacket.stream_index==gotVideoCodec){
  
          int framereaded;
  
          // Video? Ok
  
          avcodec_decode_video2(videoCodecContext,videoFrame,&framereaded,&framepacket);
  
          // Yeah, did we get it?
  
          if(framereaded && doit){
  
              AVRational millisecondbase = {1,1000};
  
              int f_number = framepacket.dts;
  
              int f_time = av_rescale_q(framepacket.dts,formatContext->streams[gotVideoCodec]->time_base,millisecondbase);
  
              currentTime=f_time;
  
              currentFrameNumber=f_number;
  
  
  
              int stWidth = videoCodecContext->width;
  
              int stHeight = videoCodecContext->height;
  
              SwsContext *ctx = sws_getContext(stWidth, stHeight, videoCodecContext->pix_fmt, stWidth,
  
              stHeight, PIX_FMT_RGB24, SWS_BICUBIC, NULL, NULL, NULL);
  
              if(ctx!=0){
  
              sws_scale(ctx,videoFrame->data,videoFrame->linesize,0,videoCodecContext->height,videoFrameRGB->data,videoFrameRGB->linesize);
  
              QImage framecapsule=QImage(stWidth,stHeight,QImage::Format_RGB888);
  
  
  
              for(int y=0;ydata[0]+y*videoFrameRGB->linesize[0],stWidth*3);
  
              }
  
              emit newFrameReady(framecapsule);
  
              sws_freeContext(ctx);
  
              }
  
  
  
          }
  
      }
  
      if(framepacket.stream_index==gotAudioCodec){
  
          // Audio? Ok
  
      }
  
      pausecontrol.unlock();
  
      av_free_packet(&framepacket);
  
  }

  Any Idea ?