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• ffmpeg decoding ogg adds samples in the end, resulting in a too long output

  20 septembre 2017, par JohanR

  When decoding a ogg file with ffmpeg, the output raw audio includes a "tail" in the end. Although ffprobe reports the correct duration in both samples and seconds, about 8ms is added to the end of the decoded file.

  This sounds to me like an encoder delay thing, and I have experience with this in mp3 (LAME tag) and m4a (ITUNSMB tag), but not with ogg.

  When I open the same ogg file in audacity, the file is decoded correctly, without the "tail" (and audacity is using ffmpeg..). So there seems to be enough information in the file to decode it correctly.

  I’m considering parsing ffprobe and truncating to duration_ts number of frames, but if there is some build flag for ffmpeg I would rather this be handled by the decoder...

  Here is an image of the same file first decoded by ffmpeg and imported as raw (with the tail), and then opened and decoded by audacity (without the tail) :

  

  Any clues ?

  Here is full ffmpeg output :

  PS D:\audio-test> .\ffmpeg\bin\ffmpeg.exe -f ogg -i sine-scale.ogg -f s16le -ar 44100 -ac 1 -acodec pcm_s16le sinescale-s16le
  
  ffmpeg version N-87327-g18821e3 Copyright (c) 2000-2017 the FFmpeg developers
  
    built with gcc 7.2.0 (GCC)
  
    configuration: --enable-gpl --enable-version3 --enable-cuda --enable-cuvid --enable-d3d11va --enable-dxva2 --enable-libmfx --enable-nvenc --enable-avisynth --enable-bzlib --enable-fontconfig --enable-frei0r --enable-gnutls --enable-iconv --enable-libass --enable-libbluray --enable-libbs2b --enable-libcaca --enable-libfreetype --enable-libgme --enable-libgsm --enable-libilbc --enable-libmodplug --enable-libmp3lame --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-libopenh264 --enable-libopenjpeg --enable-libopus --enable-librtmp --enable-libsnappy --enable-libsoxr --enable-libspeex --enable-libtheora --enable-libtwolame --enable-libvidstab --enable-libvo-amrwbenc --enable-libvorbis --enable-libvpx --enable-libwavpack --enable-libwebp --enable-libx264 --enable-libx265 --enable-libxavs --enable-libxvid --enable-libxml2 --enable-libzimg --enable-lzma --enable-zlib
  
    libavutil      55. 75.100 / 55. 75.100
  
    libavcodec     57.106.101 / 57.106.101
  
    libavformat    57. 82.100 / 57. 82.100
  
    libavdevice    57.  8.101 / 57.  8.101
  
    libavfilter     6.105.100 /  6.105.100
  
    libswscale      4.  7.103 /  4.  7.103
  
    libswresample   2.  8.100 /  2.  8.100
  
    libpostproc    54.  6.100 / 54.  6.100
  
  Input #0, ogg, from 'sine-scale.ogg':
  
    Duration: 00:00:05.00, start: 0.000000, bitrate: 23 kb/s
  
      Stream #0:0: Audio: vorbis, 44100 Hz, mono, fltp, 120 kb/s
  
  Stream mapping:
  
    Stream #0:0 -> #0:0 (vorbis (native) -> pcm_s16le (native))
  
  Press [q] to stop, [?] for help
  
  Output #0, s16le, to 'sinescale-s16le':
  
    Metadata:
  
      encoder         : Lavf57.82.100
  
      Stream #0:0: Audio: pcm_s16le, 44100 Hz, mono, s16, 705 kb/s
  
      Metadata:
  
        encoder         : Lavc57.106.101 pcm_s16le
  
  size=     431kB time=00:00:05.00 bitrate= 705.6kbits/s speed= 357x
  
  video:0kB audio:431kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: 0.000000%

• Slice a long video with ffmpeg to little pieces in node js

  24 janvier 2018, par ler

  I have a very big video like 3 hours, and I want to slice it to little pieces of 20 minutes each.
  This is my initial code :

  var fs = require('fs'); 
  
  var spawn = require('child_process').spawn;
  
  var ffmpeg = spawn("ffmpeg", [
  
      '-i', './videos/long-video.mp4',
  
      '-codec:v', 'copy', 
  
      '-codec:a', 'copy', 
  
      '-f','mp4',
  
      '-map', '0', '-f', 'segment', '-segment_time', '1200', './videos/pieces/video_%04d.mp4'
  
    ]); 

  What this code do is slice the video in pieces and save them to the location I provided, so you need to wait until the ffmpeg finish slicing the whole video.
  But what I’m looking for is a way to trigger a code when ever ffmpeg has made a new piece so I can insert the video name in database, something like this :

  var fs = require('fs'); 
  
  var spawn = require('child_process').spawn;
  
  var ffmpeg = spawn("ffmpeg", [
  
      '-i', './videos/long-video.mp4',
  
      '-codec:v', 'copy', 
  
      '-codec:a', 'copy', 
  
      '-f','mp4',
  
      '-map', '0', '-f', 'segment', '-segment_time', '1200', 
  
      'pipe:1'
  
    ]);
  
  ffmpeg.stdout.on('data', function (data) {
  
      // store the video name in database
  
      console.log('new peice has been made' );
  
    });
  
  ffmpeg.stderr.on('data', function (data) {
  
      console.log('error' );
  
    });

  ffmpeg.stdout.on doesn’t exit I just made it to indicate what I’m looking for. What does exist is ffmpeg.stdout.pipe() ; but again I don’t know how to trigger a code whenever a new piece has been made.

• ffmpeg too long filter complex string

  29 janvier 2018, par user2642511

  I have a video with an actor recorded with a green screen as background

  I want to process that video with ffmpeg in order to have a diferent zooms of it every 3 seconds or every time there is a silence in the video and use chroma to replace the backbround of every 3 seconds section with a diferent background.

  Well I made a program that charmly builds the entire filter string and tryed it with a 6 secods video and it works excelent.

  But when I use it with a 2:30 minutes video the resultant string becames 6608 charracters long, aparently that is too long for command prompt to process it.

  Well, aparently I have to change my strategy

  What would you suggest in order to achieve what I want ?

  My goal is :

  Input green screen video ----> Process ----> Same video with diferent zooms and backgrounds every 3 seconds or every time the actor gets quiet

  Thanks on advance