typescript - 将 ffmpeg 管道传输到 flac 编码器时出现问题

Question

我需要使用 seektables 对 flac 文件进行编码，ffmpeg 的 flac 编码器不包括 seektables，所以我需要使用 flac CLI。我试图通过先通过 ffmpeg 将任意音频文件转换为可搜索的 flac 文件，然后将其转换为 flac 编码器。

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)
  })
}

虽然此代码有效，但生成的 flac 文件不正确。源音频的持续时间为 06:14，但 flac 文件的持续时间为 06:45:47。手动编码 flac 而无需将 ffmpeg 传输到它可以正常工作，但我无法在需要使用流的服务器环境中这样做。

这是转码时 flac 编码器的输出:

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

Answer 1

要事第一:

I need to encode a flac file with seektables,
-: WARNING, cannot write back seekpoints when encoding to stdout

来自 flac -H:

A single INPUTFILE may be - for stdin.  No INPUTFILE implies stdin.  Use of
stdin implies -c (write to stdout).  Normally you should use:
   flac [options] -o outfilename  or  flac -d [options] -o outfilename
instead of:
   flac [options] > outfilename   or  flac -d [options] > outfilename
since the former allows flac to seek backwards to write the STREAMINFO or
WAVE/AIFF header contents when necessary.

尝试使用 flac - -o outfilename.flac 而不是 flac -

它似乎对我有用并且生成的音频长度正确(在我的情况下 - 虽然与您的不同):
$ rm out.flac; ffmpeg -nostdin -i ~/audio/asmr/ASMR\_\Camera\Touching\_\No\Mouthsounds\_\NO\TALKING-lQlZJ82ebBk.m4a -f wav - | flac - -o 输出.flac

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.

ffmpeg version n4.1.3 Copyright (c) 2000-2019 the FFmpeg developers
  built with gcc 8.2.1 (GCC) 20181127
  configuration: --prefix=/usr --disable-debug --disable-static --disable-stripping --enable-fontconfig --enable-gmp --enable-gnutls --enable-gpl --enable-ladspa --enable-libaom --enable-libass --enable-libbluray --enable-libdrm --enable-libfreetype --enable-libfribidi --enable-libgsm --enable-libiec61883 --enable-libjack --enable-libmodplug --enable-libmp3lame --enable-libopencore_amrnb --enable-libopencore_amrwb --enable-libopenjpeg --enable-libopus --enable-libpulse --enable-libsoxr --enable-libspeex --enable-libssh --enable-libtheora --enable-libv4l2 --enable-libvidstab --enable-libvorbis --enable-libvpx --enable-libwebp --enable-libx264 --enable-libx265 --enable-libxcb --enable-libxml2 --enable-libxvid --enable-nvdec --enable-nvenc --enable-omx --enable-shared --enable-version3
  libavutil      56. 22.100 / 56. 22.100
  libavcodec     58. 35.100 / 58. 35.100
  libavformat    58. 20.100 / 58. 20.100
  libavdevice    58.  5.100 / 58.  5.100
  libavfilter     7. 40.101 /  7. 40.101
  libswscale      5.  3.100 /  5.  3.100
  libswresample   3.  3.100 /  3.  3.100
  libpostproc    55.  3.100 / 55.  3.100
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from '/home/user/audio/asmr/ASMR _ Camera Touching _ No Mouthsounds _ NO TALKING-lQlZJ82ebBk.m4a':
  Metadata:
    major_brand     : isom
    minor_version   : 512
    compatible_brands: isomiso2mp41
    encoder         : Lavf58.3.100
  Duration: 00:53:29.09, start: 0.000000, bitrate: 126 kb/s
    Stream #0:0(und): Audio: aac (LC) (mp4a / 0x6134706D), 44100 Hz, stereo, fltp, 125 kb/s (default)
    Metadata:
      handler_name    : SoundHandler
Stream mapping:
  Stream #0:0 -> #0:0 (aac (native) -> pcm_s16le (native))
Output #0, wav, to 'pipe:':
  Metadata:
    major_brand     : isom
    minor_version   : 512
    compatible_brands: isomiso2mp41
    ISFT            : Lavf58.20.100
    Stream #0:0(und): Audio: pcm_s16le ([1][0][0][0] / 0x0001), 44100 Hz, stereo, s16, 1411 kb/s (default)
    Metadata:
      handler_name    : SoundHandler
      encoder         : Lavc58.35.100 pcm_s16le
-: WARNING: skipping unknown chunk 'LIST' (use --keep-foreign-metadata to keep)
13% complete, ratio=0.284size=  552816kB time=00:53:29.09 bitrate=1411.2kbits/s speed= 665x      
video:0kB audio:552816kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: 0.000014%
-: WARNING: unexpected EOF; expected 1073741823 samples, got 141516800 samples
13% complete, ratio=0.283

$ ffprobe ./out.flac 
ffprobe version n4.1.3 Copyright (c) 2007-2019 the FFmpeg developers
  built with gcc 8.2.1 (GCC) 20181127
  configuration: --prefix=/usr --disable-debug --disable-static --disable-stripping --enable-fontconfig --enable-gmp --enable-gnutls --enable-gpl --enable-ladspa --enable-libaom --enable-libass --enable-libbluray --enable-libdrm --enable-libfreetype --enable-libfribidi --enable-libgsm --enable-libiec61883 --enable-libjack --enable-libmodplug --enable-libmp3lame --enable-libopencore_amrnb --enable-libopencore_amrwb --enable-libopenjpeg --enable-libopus --enable-libpulse --enable-libsoxr --enable-libspeex --enable-libssh --enable-libtheora --enable-libv4l2 --enable-libvidstab --enable-libvorbis --enable-libvpx --enable-libwebp --enable-libx264 --enable-libx265 --enable-libxcb --enable-libxml2 --enable-libxvid --enable-nvdec --enable-nvenc --enable-omx --enable-shared --enable-version3
  libavutil      56. 22.100 / 56. 22.100
  libavcodec     58. 35.100 / 58. 35.100
  libavformat    58. 20.100 / 58. 20.100
  libavdevice    58.  5.100 / 58.  5.100
  libavfilter     7. 40.101 /  7. 40.101
  libswscale      5.  3.100 /  5.  3.100
  libswresample   3.  3.100 /  3.  3.100
  libpostproc    55.  3.100 / 55.  3.100
Input #0, flac, from './out.flac':
  Duration: 00:53:29.09, start: 0.000000, bitrate: 399 kb/s
    Stream #0:0: Audio: flac, 44100 Hz, stereo, s16

$ ffprobe ~/audio/asmr/ASMR\ _\ Camera\ Touching\ _\ No\ Mouthsounds\ _\ NO\ TALKING-lQlZJ82ebBk.m4a
ffprobe version n4.1.3 Copyright (c) 2007-2019 the FFmpeg developers
  built with gcc 8.2.1 (GCC) 20181127
  configuration: --prefix=/usr --disable-debug --disable-static --disable-stripping --enable-fontconfig --enable-gmp --enable-gnutls --enable-gpl --enable-ladspa --enable-libaom --enable-libass --enable-libbluray --enable-libdrm --enable-libfreetype --enable-libfribidi --enable-libgsm --enable-libiec61883 --enable-libjack --enable-libmodplug --enable-libmp3lame --enable-libopencore_amrnb --enable-libopencore_amrwb --enable-libopenjpeg --enable-libopus --enable-libpulse --enable-libsoxr --enable-libspeex --enable-libssh --enable-libtheora --enable-libv4l2 --enable-libvidstab --enable-libvorbis --enable-libvpx --enable-libwebp --enable-libx264 --enable-libx265 --enable-libxcb --enable-libxml2 --enable-libxvid --enable-nvdec --enable-nvenc --enable-omx --enable-shared --enable-version3
  libavutil      56. 22.100 / 56. 22.100
  libavcodec     58. 35.100 / 58. 35.100
  libavformat    58. 20.100 / 58. 20.100
  libavdevice    58.  5.100 / 58.  5.100
  libavfilter     7. 40.101 /  7. 40.101
  libswscale      5.  3.100 /  5.  3.100
  libswresample   3.  3.100 /  3.  3.100
  libpostproc    55.  3.100 / 55.  3.100
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from '/home/user/audio/asmr/ASMR _ Camera Touching _ No Mouthsounds _ NO TALKING-lQlZJ82ebBk.m4a':
  Metadata:
    major_brand     : isom
    minor_version   : 512
    compatible_brands: isomiso2mp41
    encoder         : Lavf58.3.100
  Duration: 00:53:29.09, start: 0.000000, bitrate: 126 kb/s
    Stream #0:0(und): Audio: aac (LC) (mp4a / 0x6134706D), 44100 Hz, stereo, fltp, 125 kb/s (default)
    Metadata:
      handler_name    : SoundHandler

$ vlc out.flac
#sounds ok, even at the end

这个
-:警告:跳过未知 block “LIST”(使用 --keep-foreign-metadata 保留)
没办法:
错误:从 stdin 或到 stdout 编码时不能使用 --keep-foreign-metadata

然而，即使我得到
-:警告:意外的 EOF；预期 1073741823 个样本，得到 141516800 个样本
这就是它停在 13% (141516800 * 100/1073741823 = 13.2%) 的原因，输出看起来很好并且与输入的长度相同!

更新:发生这种情况是因为 ffmpeg 没有填写正确的 ChunkSize输出 wav 的值，因为它被发送到管道而不是文件，所以 ffmpeg 最初使用四个 0xFF 字节作为 ChunkSize，当 wav 编码完成时，ffmpeg 知道正确的值是什么会，但它不能返回输出管道来更新 ChunkSize 部分。当输出到文件时，它可以。

The canonical WAVE format starts with the RIFF header:

0         4   ChunkID          Contains the letters "RIFF" in ASCII form
                               (0x52494646 big-endian form).
4         4   ChunkSize        36 + SubChunk2Size, or more precisely:
                               4 + (8 + SubChunk1Size) + (8 + SubChunk2Size)
                               This is the size of the rest of the chunk 
                               following this number.  This is the size of the 
                               entire file in bytes minus 8 bytes for the
                               two fields not included in this count:
                               ChunkID and ChunkSize.
8         4   Format           Contains the letters "WAVE"
                               (0x57415645 big-endian form).

下面是 ffmpeg wav 输出到文件时与输出到管道时的不同之处:

(注意:不要运行它，即使在快速处理器上，它也需要几分钟的 100% CPU 使用率，也就是一个内核)

$ colordiff -up <(hexdump -C toafile.wav) <(hexdump -C piped.wav)
--- /dev/fd/63  2019-05-19 21:28:20.621944056 +0200
+++ /dev/fd/62  2019-05-19 21:28:20.621944056 +0200
@@ -1,8 +1,8 @@
-00000000  52 49 46 46 46 c0 bd 21  57 41 56 45 66 6d 74 20  |RIFFF..!WAVEfmt |
+00000000  52 49 46 46 ff ff ff ff  57 41 56 45 66 6d 74 20  |RIFF....WAVEfmt |
 00000010  10 00 00 00 01 00 02 00  44 ac 00 00 10 b1 02 00  |........D.......|
 00000020  04 00 10 00 4c 49 53 54  1a 00 00 00 49 4e 46 4f  |....LIST....INFO|
 00000030  49 53 46 54 0e 00 00 00  4c 61 76 66 35 38 2e 32  |ISFT....Lavf58.2|
-00000040  37 2e 31 30 33 00 64 61  74 61 00 c0 bd 21 00 00  |7.103.data...!..|
+00000040  37 2e 31 30 33 00 64 61  74 61 ff ff ff ff 00 00  |7.103.data......|
 00000050  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
 *
 00003440  00 00 01 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
-----------

1. 管道 wav(当输出到管道时由 ffmpeg 生成)将因此导致 flac 给你 1 个额外警告:

一个。生成管道 wav: ffmpeg -nostdin -i ~/audio/asmr/ASMR\_\Camera\Touching\_\No\Mouthsounds\_\NO\TALKING-lQlZJ82ebBk.m4a -f wav -> piped.wav

将其通过管道传输到 flac:

cat piped.wav | flac - -o out2.flac

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)
-: 13% complete, ratio=0.284-: WARNING: unexpected EOF; expected 1073741823 samples, got 141516800 samples
13% complete, ratio=0.283

flac 不知道输入的正确大小(ChunkSize 是 0xFFFFFFFF)

1. 但是 wav 文件(当输出到文件时由 ffmpeg 生成)是没问题的:

一个。生成wav文件:ffmpeg -nostdin -i ~/audio/asmr/ASMR\_\Camera\Touching\_\No\Mouthsounds\_\NO\TALKING-lQlZJ82ebBk.m4a -f wav toafile.wav

将其通过管道传输到 flac:

$ rm out2.flac; cat toafile.wav | flac - -o out2.flac

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)
-: wrote 160381819 bytes, ratio=0.283

这是因为它的 ChunkSize 值设置正确。 (ChunkSize 为 0x21BDC046 = 566,083,654，比总大小为 566,083,662 字节的输出 infile.wav 少 8 个字节)