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• FFProbe generated data don't seem to agree with calculated data using ffmpeg libraries

  18 janvier 2020, par ark1974

  Using ffmpeg library avformat I am trying to check if the ffprobe generated data agrees with the data generated by the library. The code objective is to try to seek to the nearest key frame. When trying to seek at 100 frame or less, the codes returns 0 all the time.
  When trying to seek at 200 frame, the codes returns 4 all the time. But the result ie 4th frame don’t seem to be right. Where am I wrong ? Is my time_base conversion to actual frame faulty ?

  The test result using ffprobe

  Filename = test.mp4  
  
  Duration = 00:00:10.56 
  
  Fps = 25
  
  Total frames = 256   
  
  The key frames pkt_pts_time are at 2.120000  and 0.000000 (using -skip_frame nokey )
  
  Corresponding pkt_duration_time: 0.040000 and 0.040000 (  same, why?)

  Abstract of the code :

  // Objective: seek to the nearest key frame
  
  frameIndex = 200;
  
  int64_t timeBase = (int64_t(pCodecCtx->time_base.num) * AV_TIME_BASE) / int64_t(pCodecCtx->time_base.den);  
  
  int64_t seekTarget = int64_t(frameIndex) * timeBase;
  
  
  
  if (av_seek_frame(pFormatCtx, -1, seekTarget, AVSEEK_FLAG_FRAME | AVSEEK_FLAG_BACKWARD) < 0) return -1;
  
  
  
  //convert the time_base to actual frame
  
  auto time2frame = [&](int64_t tb) {
  
      return tb * int64_t(pCodecCtx->time_base.den) / (int64_t(pCodecCtx->time_base.num) * AV_TIME_BASE);
  
  };
  
  
  
  AVPacket avPacket;
  
  int result = av_read_frame(pFormatCtx, &avPacket);
  
  if (result == 0) {
  
  
  
      auto dts = avPacket.dts;
  
      auto pts = avPacket.pts;
  
      auto idx = avPacket.stream_index;
  
      auto f = time2frame(pts); // expecting the actual frame here
  
      std::cout << dts << pts << idx << f;
  
  }

• FFmpeg stucks for few seconds on start

  7 février 2018, par tarasmorskyi

  I’m trying to cut and resize video on Android(but it is similar on MacOS) , but when I run the ffmpeg command it returns me

  frame= 0 fps=0.0 q=0.0 size= 0kB time=00:00:00.00 bitrate=N/A speed=

  It repeats for about 20 sec (I have 4K video with 3 sec duration).

  Is there any way to improve process speed ? Here is example of my ffmpeg command

  ffmpeg -y -i input.mp4 -ss 00:01.82 -to 00:02.94 -vf scale=500:1024 -c:v libx264 -c:a aac -b:v 500k -b:a 96k output.mp4

• FFMPEG - avformat_open_input() always return error with filename

  22 septembre 2015, par Tony Than

  const char* filename = "D:\\abc.flv";
  
  err = avformat_open_input(&ic, filename, NULL, 0);

  This function always returns error when filename is *.flv.
  If I use file mp4 (*.mp4), it’s ok.

  Please help me find the cause of this problem !!