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

  30 September 2022, by 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!

  


• FFmpeg amix-filter always does "volume normalization". How to prevent it and what are the possible drawbacks of it?

  14 June 2020, by Chitrang

  There are many questions on this topic link1, link2, and link3. However, I am asking for suggestions on the probable solution and if it has some drawbacks.

  



  Problem Definition: amix-filter always does "volume normalization" and can't be turned off

  



  Reference: Please read comments over here by @Reino. He also had opened a ticket on the FFmpeg forum to explain the situation.

  



  Hacky Solution: amix=inputs=13:dropout_transition=1000,volume=13

  



  Reference: Answered here, and also in the ticket.

  



  Questions:

  



  1) "amix scales each input's volume by 1/n where n = no. of active inputs. This is evaluated for each audio frame. So when an input drops out, the volume of the remaining inputs is scaled by a smaller amount, hence their volumes increase."Refer

  



  For example, if I am merging 10 audio streams then, the 1st audio stream will be scaled by 1/10, 2nd by 1/9, 3rd by 1/8 .. 9th by 1/2 and last 10th by 1. Have I understood this correctly or let me know if I am missing something?

  



  2) dropout_transition: The transition time, in seconds, for volume renormalization when an input stream ends. The default value is 2 seconds.

  



  dropout_transition means it will SKIP given seconds, right? So if I set dropout_transition=1000(very large number) then regardless of video length FFmpeg will drop/skip audio transition for provided seconds. Again, please do correct me if I have made wrong assumption.

  



  3) I have tried many other solutions without any luck and now I am relying profoundly on the provided solution. Is there any drawback to the above hacky solution?

  


• Changing Audio Volume using FFmpeg Android Error

  23 August 2018, by kataroty

  I am using FFmpeg and I need to change the volume of the Audio.

  This is the command that should change the volume of the audio :

  ffmpeg -i input.wav -filter:a "volume=1.5" output.wav

  I read from somewhere that it had to overwrite the file if it already existed so either one had to delete the file or use -y. When I tried to do it without the -y command it never got to onSuccess() or ´onFailure(), but it always printed out the onStart() message.

  String[] cmdy = { "-i -y" , pcmtowavTempFile.toString(),  "-af", "volume=5", pcmtowavTempFile.toString()};
  
      ffmpeg.execute(cmdy, new ExecuteBinaryResponseHandler() {
  
  
  
          @Override
  
          public void onStart() {
  
              System.out.println("ayy: onStart");
  
          }
  
  
  
          @Override
  
          public void onSuccess(String message) {
  
              System.out.println("ayy: onSuccess");
  
              super.onSuccess(message);
  
          }
  
          @Override
  
          public void onFailure(String message) {
  
              System.out.println("ayy: onFailure " + message);
  
              super.onFailure(message);
  
          }
  
  });

  At the moment I get this error:

  ffmpeg version n4.0-39-gda39990 Copyright (c) 2000-2018 the FFmpeg developers
  
    built with gcc 4.9.x (GCC) 20150123 (prerelease)
  
    configuration: --target-os=linux --cross-prefix=/root/bravobit/ffmpeg-android/toolchain-android/bin/arm-linux-androideabi- --arch=arm --cpu=cortex-a8 --enable-runtime-cpudetect --sysroot=/root/bravobit/ffmpeg-android/toolchain-android/sysroot --enable-pic --enable-libx264 --enable-ffprobe --enable-libopus --enable-libvorbis --enable-libfdk-aac --enable-libfreetype --enable-libfribidi --enable-libmp3lame --enable-fontconfig --enable-libvpx --enable-libass --enable-yasm --enable-pthreads --disable-debug --enable-version3 --enable-hardcoded-tables --disable-ffplay --disable-linux-perf --disable-doc --disable-shared --enable-static --enable-runtime-cpudetect --enable-nonfree --enable-network --enable-avresample --enable-avformat --enable-avcodec --enable-indev=lavfi --enable-hwaccels --enable-ffmpeg --enable-zlib --enable-gpl --enable-small --enable-nonfree --pkg-config=pkg-config --pkg-config-flags=--static --prefix=/root/bravobit/ffmpeg-android/build/armeabi-v7a --extra-cflags='-I/root/bravobit/ffmpeg-android/toolchain-android/include -U_FORTIFY_SOURCE -D_FORTIFY_SOURCE=2 -fno-strict-overflow -fstack-protector-all' --extra-ldflags='-L/root/bravobit/ffmpeg-android/toolchain-android/lib -Wl,-z,relro -Wl,-z,now -pie' --extra-cxxflags=
  
    libavutil      56. 14.100 / 56. 14.100
  
    libavcodec     58. 18.100 / 58. 18.100
  
    libavformat    58. 12.100 / 58. 12.100
  
    libavdevice    58.  3.100 / 58.  3.100
  
    libavfilter     7. 16.100 /  7. 16.100
  
    libavresample   4.  0.  0 /  4.  0.  0
  
    libswscale      5.  1.100 /  5.  1.100
  
    libswresample   3.  1.100 /  3.  1.100
  
    libpostproc    55.  1.100 / 55.  1.100
  
  Unrecognized option 'i -y'.

  Which clearly states that it does not recognize option i -y, but also as I said earlier then if I remove the -y it never gets to onSuccess() or onFailure().

  help me to find a solution. Thanks.