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• HTML5 : Apply volume to cloned sounds in HTML5 multiShot case.

  18 août 2013, par scottschiller

  HTML5 : Apply volume to cloned sounds in HTML5 multiShot case.

• 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 !

  


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

  14 juin 2020, par 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 ?