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• Processing Frames of Screen Recording in Node Usin FFMPEG

  28 septembre 2020, par The42ndTurtle

  I am trying to capture my screen using Node.JS and FFMPEG, and I have gotten as far as saving an flv file, but I am unable to process the frames real-time.

  


  My code so far is

  


  const ffmpeg = require('ffmpeg-static');
const {spawn} = require('child_process');
const {createWriteStream} = require('fs');

const canvas = document.querySelector('#canvas');
const ctx = canvas.getContext('2d');

const process = spawn(
  ffmpeg,
  ["-f", "gdigrab", "-framerate", "30", "-i", "desktop", '-crf', '0', '-preset', 'ultrafast', '-f', 'flv', '-'],
  { stdio: "pipe" }
);


const stream = process.stdout;

const file = createWriteStream('capture.flv');
stream.pipe(file);

stream.on('data', chunk => {
  const base64 = chunk.toString('base64');
  const data = `data:image/png;base64,${base64}`;

  const image = new Image();
  image.src = data;
  ctx.drawImage(image, 0, 0);
});



  


  The output.flv file that is created is fine, but the image getting created in the stream does not seem to be a valid image. When I log the base64 and try just turning the single string into an image, it appears to be invalid image data. I want to use the stream to capture each frame of the stream.

  


• ffmpeg/sox audio processing : Merging files with envelope changes

  2 octobre 2020, par March Hare

  So I have two audio files. One is a music bed with an intro that segues into a looping music clip (let's call this *1). The second is the voice over audio track (referenced as *2, length n).

  


  Audio *1 is fixed, while the voice over (*2) is downloaded about 3 times a day, and can vary in length. *1 is longer than we ever expect *2 to be.

  


  What I need to do is

  


  

  1. Alter the overall gain of *1 to -7.5 dB

  


  2. Begin merging VO *2 at time m, while reducing the volume envelope of *1 by -11 dB. This is fixed based on the length of the intro.

  


  3. Fade everything out to -∞ dB around the end of *2

  


  4. Trim off the silence at the end.
For reference, the total length of the final track should be m+n.

  


  


  Unfortunately, I'm not versed enough with ffmpeg or sox to know exactly what I'm after here, and a lot of the examples tend to do one thing or another and aren't always clear when combining happens. I didn't get a lot of prior notice about this coming down the pipeline, so I'd like to get something relatively quick. We're able to do all of this stuff nicely in Adobe Audition (and I can do something similar in Audacity), but the idea is to automate it. For our envelope adjustments, we were just using linear ramps rather than smoothsteps, and that sounded fine.

  


  The TLDR : The VO track *2 governs how long the file winds up being, while audio bed *1 needs to be ducked when *2 begins, and the whole thing faded out right when *2 ends.

  


  We also have an automation system (radio station automation, specialized for something different than I need), so in a pinch if we have to just cut off the audio at the end of *2, we can get the fadeout from the radio automation system.

  


  I've been using the information at this link to some effect (specifically the bit about ffmpeg volumes), but it still isn't dynamic enough for the situation.
Envelope pattern in SoX (Sound eXchange) or ffmpeg

  


  Anyone have any advice on this one ? I've got Sox and ffmpeg available, and if need be I can probably install other tools as well.

  


• avfilter/af_aiir : implement parallel processing

  15 octobre 2020, par Paul B Mahol

  avfilter/af_aiir : implement parallel processing
  

  • [DH] doc/filters.texi
  • [DH] libavfilter/af_aiir.c