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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;
  
  }

• Merge pull request #253 from zeroclipboard/origins-array-bug

  17 octobre 2013, par jonrohan

  Merge pull request #253 from zeroclipboard/origins-array-bug
  Array.push returns a number, not an array.
  

• Spawned ffmpeg process in nodejs Transform stream with flow control doesn't process input stream

  30 septembre 2022, par user1832894

  I have implemented a node.js Transform stream class that spawns ffmpeg and streams out the transformed stream at a controlled realtime rate. Below is my _transform() method.

  


  this.rcvd += chunk.length
console.log('received bytes %d', this.rcvd)
const ready = this.ffmpeg.stdin.write(chunk, encoding, err => err
  ? cb(err)
  : ready
    ? cb
    : this.ffmpeg.stdin.once('drain', cb))


  


  I want to write to ffmpeg's stdin stream till it returns false, at which point I wait for the drain event to write more data.

  


  Concurrently, I have a timer that fires every 40 milliseconds that reads ffmpeg's stdout and pushes it to the Transform stream's output (the readable side). Code not complete, but the folllowing describes it well.

  


  const now = Date.now()
const bytesToTransmit = (now - this.lastTx) * 32

const buf = this.ffmpeg.stdout.read()

if (buf == null) return

if (buf.length <= bytesToTransmit) {
  this.push(buf)
  this.lastTx += buf.length * 32
  return
}

this.push(buf.slice(0, bytesToTransmit))
this.lastTx = now

// todo(handle pending buffer)
this.pending = buf.slice(bytesToTransmit)


  


  The issue I am facing is that the first write (of 65k bytes) returns false, and after that I never receive the drain event. FFMpeg doesn't start processing the data until certain amount of data (256k bytes in my case) has been written, and once I start waiting for the drain event, I never recover control.

  


  I've tried a few ffmpeg options like nobuffer but to no avail. What am I doing wrong ? Any ideas would be super helpful.

  


  Thanks !