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• Problems piping ffmpeg to flac encoder

  19 mai 2019, par Sebastian Olsen

  I need to encode a flac file with seektables, ffmpeg’s flac encoder does not include seektables, so I need to use the flac CLI. I’m trying to make it possible to convert any arbitrary audio file to a seekable flac file by first piping it through ffmpeg, then to the flac encoder.

  export const transcodeToFlac: AudioTranscoder<{}> = ({
  
    source,
  
    destination
  
  }) => {
  
    return new Promise((resolve, reject) => {
  
      let totalSize = 0
  
  
  
      const { stdout: ffmpegOutput, stderr: ffmpegError } = spawn("ffmpeg", [
  
        "-i",
  
        source,
  
        "-f",
  
        "wav",
  
        "pipe:1"
  
      ])
  
  
  
      const { stdout: flacOutput, stdin: flacInput, stderr: flacError } = spawn(
  
        "flac",
  
        ["-"]
  
      )
  
  
  
      flacOutput.on("data", (buffer: Buffer) => {
  
        totalSize += buffer.byteLength
  
      })
  
  
  
      ffmpegError.on("data", error => {
  
        console.log(error.toString())
  
      })
  
  
  
      flacError.on("data", error => {
  
        console.log(error.toString())
  
      })
  
  
  
      //stream.on("error", reject)
  
  
  
      destination.on("finish", () => {
  
        resolve({
  
          mime: "audio/flac",
  
          size: totalSize,
  
          codec: "flac",
  
          bitdepth: 16,
  
          ext: "flac"
  
        })
  
      })
  
  
  
      ffmpegOutput.pipe(flacInput)
  
      flacOutput.pipe(destination)
  
    })
  
  }

  While this code works, the resulting flac file is not correct. The source audio is of duration 06:14, but the flac file is of duration 06:45:47. Encoding the flac manually without piping ffmpeg to it works fine, but I cannot do that in a server environment where I need to utilize streams.

  Here’s what the flac encoder outputs when transcoding :

  flac 1.3.2
  
  Copyright (C) 2000-2009  Josh Coalson, 2011-2016  Xiph.Org Foundation
  
  flac comes with ABSOLUTELY NO WARRANTY.  This is free software, and you are
  
  welcome to redistribute it under certain conditions.  Type `flac' for details.
  
  
  
  -: WARNING: skipping unknown chunk 'LIST' (use --keep-foreign-metadata to keep)
  
  -: WARNING, cannot write back seekpoints when encoding to stdout
  
  -: 0% complete, ratio=0.357
  
  0% complete, ratio=0.432
  
  0% complete, ratio=0.482
  
  0% complete, ratio=0.527
  
  0% complete, ratio=0.541
  
  1% complete, ratio=0.554
  
  1% complete, ratio=0.563
  
  1% complete, ratio=0.571
  
  size=   36297kB time=00:03:30.70 bitrate=1411.2kbits/s speed= 421x
  
  1% complete, ratio=0.572
  
  1% complete, ratio=0.570
  
  1% complete, ratio=0.577
  
  1% complete, ratio=0.583
  
  1% complete, ratio=0.584
  
  1% complete, ratio=0.590
  
  1% complete, ratio=0.592
  
  size=   64512kB time=00:06:14.49 bitrate=1411.2kbits/s speed= 421x
  
  video:0kB audio:64512kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead:
  
  0.000185%
  
  
  
  -: WARNING: unexpected EOF; expected 1073741823 samples, got 16510976 samples
  
  2% complete, ratio=0.579

• FFmpeg : Remux f4v cutted from stream to mp4

  13 mai 2019, par Martin

  I have a mp4 file cutted from a H.264/AAC stream with Wowza Media Server.
  After the cutting, the file was forced to mp4 format with the following command :

  ffmpeg -i wowza_output_file -vcodec copy -acodec copy -f mp4 -y wowza_output_file_copy

  From there I renamed it to test_f4v.mp4 and took ffprobe, to take a look at the file :

  ffprobe version 0.8, Copyright (c) 2007-2011 the FFmpeg developers
  
    built on Jul 20 2011 13:32:19 with gcc 4.4.3
  
    configuration: --enable-gpl --enable-version3 --enable-nonfree --enable-postproc --enable-libfaac --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-libtheora --enable-libvorbis --enable-libx264
  
    libavutil    51.  9. 1 / 51.  9. 1
  
    libavcodec   53.  7. 0 / 53.  7. 0
  
    libavformat  53.  4. 0 / 53.  4. 0
  
    libavdevice  53.  1. 1 / 53.  1. 1
  
    libavfilter   2. 23. 0 /  2. 23. 0
  
    libswscale    2.  0. 0 /  2.  0. 0
  
    libpostproc  51.  2. 0 / 51.  2. 0
  
  Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'test_f4v.mp4':
  
    Metadata:
  
      major_brand     : f4v 
  
      minor_version   : 0
  
      compatible_brands: isommp42m4v 
  
      creation_time   : 2012-04-23 12:36:06
  
    Duration: 01:00:01.84, start: 0.000000, bitrate: 2004 kb/s
  
      Stream #0.0(eng): Video: h264 (Baseline), yuv420p, 854x480 [PAR 1:1 DAR 427:240], 1903 kb/s, 25 fps, 25 tbr, 90k tbn, 50 tbc
  
      Metadata:
  
        creation_time   : 2012-04-23 12:36:06
  
      Stream #0.1(eng): Audio: aac, 48000 Hz, stereo, s16, 96 kb/s
  
      Metadata:
  
        creation_time   : 2012-04-23 12:36:06

  Now there is a problem. I need a file, which has the following meta data :

  major_brand     : mp42
  
  compatible_brands: isom

  Is there a way to remux the mp4 file to get the major_brand and compatible_brands to the described values with ffmpeg ?

• How to split a .mkv file into sounds and vedio file ?

  13 février 2020, par Ken Yip

  I have a mkv file which contain 3 streams. I use ffprobe to get the info of my mkv file.

  ffprobe ./demo/test2.mkv 

  I got this output

  Input #0, matroska,webm, from './demo/test2.mkv':
  
  Metadata:
  
  encoder         : libebml v0.7.7 + libmatroska v0.8.1
  
  creation_time   : 2011-02-16T16:06:17.000000Z
  
  Duration: 00:03:41.08, start: 0.000000, bitrate: 1363 kb/s
  
  Stream #0:0: Video: rv40, yuv420p, 720x480, SAR 1:1 DAR 3:2, 29.97 tbr, 1k tbn, 1k tbc (default)
  
  Stream #0:1: Audio: aac (LC), 48000 Hz, stereo, fltp (default)
  
  Stream #0:2: Audio: aac (LC), 48000 Hz, stereo, fltp

  The audio streams should be vocal and background music. I would like to extract them from the video.

  I have try to do so with those command

  ffmpeg -i ./demo/test2.mkv -map_channel 0.1.0 -y ch0.wav -map_channel 0.2.0 -y ch1.wav

  However, it output the same audio file. Is there any mistake I have made ? Thanks a lot.