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• How to stop perl buffering ffmpeg output

  4 février 2017, par Sebastian King

  I am trying to have a Perl program process the output of an ffmpeg encode, however my test program only seems to receive the output of ffmpeg in periodic chunks, thus I am assuming there is some sort of buffering going on. How can I make it process it in real-time ?

  My test program (the tr command is there because I thought maybe ffmpeg’s carriage returns were causing perl to see one big long line or something) :

  #!/usr/bin/perl
  
  
  
  $i = "test.mkv"; # big file, long encode time
  
  $o = "test.mp4";
  
  
  
  open(F, "-|", "ffmpeg -y -i '$i' '$o' 2>&1 | tr '\r' '\n'")
  
          or die "oh no";
  
  
  
  while(<f>) {
  
          print "A12345: $_"; # some random text so i know the output was processed in perl
  
  }
  
  </f>

  Everything works fine when I replace the ffmpeg command with this script :

  #!/bin/bash
  
  
  
  echo "hello";
  
  
  
  for i in `seq 1 10`; do
  
          sleep 1;
  
          echo "hello $i";
  
  done
  
  
  
  echo "bye";

  When using the above script I see the output each second as it happens. With ffmpeg it is some 5-10 seconds or so until it outputs and will output sometimes 100 lines each output.

  I have tried using the program unbuffer ahead of ffmpeg in the command call but it seems to have no effect. Is it perhaps the 2>&1 that might be buffering ?
  Any help is much appreciated.

  If you are unfamiliar with ffmpeg’s output, it outputs a bunch of file information and stuff to STDOUT and then during encoding it outputs lines like

  frame=  332 fps= 93 q=28.0 size=     528kB time=00:00:13.33 bitrate= 324.2kbits/s speed=3.75x

  which begin with carriage returns instead of new lines (hence tr) on STDERR (hence 2>&1).

• ffmpeg : Generate empty audio and video (working for video)

  17 septembre 2021, par David Ferris

  I'm trying to generate a black video with FFMPEG. I have accomplished this with the following :

  


  ffmpeg -t 5 -f lavfi -i color=c=black:s=1920x1080 -c:v libx264 -tune stillimage -pix_fmt yuv420p out.mp4


  


  Unfortunately this video doesn't have any audio tracks. Following this, I have tried to insert -i anullsrc=channel_layout=stereo:sample_rate=44100 :

  


  ffmpeg -t 5 -i anullsrc=channel_layout=stereo:sample_rate=44100 -f lavfi -i color=c=black:s=1920x1080 -c:v libx264 -tune stillimage -pix_fmt yuv420p out.mp4


  


  Unfortunately this gives the error :

  


  


  anullsrc=channel_layout=stereo:sample_rate=44100 : No such file or
directory

  


  


  How can I modify my initial script to generate a video with empty audio ?

  


• Video player scroll doesn't work after ffmpeg audio and video merge (NodeJS)

  1er novembre 2022, par Pietro Leto

  I made youtube downloader to download video from youtube using nodejs library ytdl-core. If I wanted to download video with best quality I had to download them without sound. So, in my script, I download audio and video separately and I merge them into an mp4 file.
What's the problem ? Video player scroll doesn't work. I can see the video but I can't going back or move on, and I can't see video duration.

  


  const express = require("express");
const cors = require("cors");
const app = express();
const ffmpeg = require('ffmpeg-static');
const cp = require('child_process');
const ytdl = require("ytdl-core");

app.use(cors());

app.listen(3000, () => {
    console.log("Server is working at port 3000 !!");
});

app.get('/download', (req,res) => {
    var url = req.query.URL;
    var formato = req.query.FORMAT;

    try {
        let vid = ytdl(url,{filter:'videoonly', quality:'highestvideo'})
        let aud = ytdl(url, {filter: 'audioonly', quality:'highestaudio'});

        ytdl.getInfo(url).then(info => {
            titolo = info.videoDetails.title;

            res.header("Content-Disposition", 'attachment;  filename=' + titolo + '.mp4');

            const ffmpegProcess = cp.spawn(ffmpeg, [
                '-i', `pipe:3`,
                '-i', `pipe:4`,
                '-map','0:v:0',
                '-map','1:a:0',
                '-c:v', 'copy',
                '-c:a', 'aac',
                '-crf','27',
                '-preset','veryfast',
                '-movflags','frag_keyframe+empty_moov',
                '-f','mp4',
                '-loglevel','error',
                '-'
            ], {
                stdio: [
                'pipe', 'pipe', 'pipe', 'pipe', 'pipe',
                ],
            });
              
            aud.pipe(ffmpegProcess.stdio[4]);
            vid.pipe(ffmpegProcess.stdio[3]);
            ffmpegProcess.stdio[1].pipe(res);
        });
    }
    catch(err) {
        console.log("Error with URL: " + url + "\nERROR: " + err + "\n\n");
    }
});


  


  I have not found alternatives to do this. I need a working script to download youtube videos with good quality.