我需要使用seektables编码flac文件，ffmpeg的flac编码器不包含seektables，因此我需要使用flac CLI。我试图通过先通过ffmpeg用管道将其转换为flac编码器，然后再将其转换为flac编码器，来将任意音频文件转换为可搜索的flac文件。
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)
})
}
尽管此代码有效，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。在不使用ffmpeg对其进行手动编码的情况下，手动编码flac可以正常工作，但是在需要利用流的服务器环境中，我无法做到这一点。
以下是flac编码器在转码时输出的内容：
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
答案 0 :(得分：1)
第一件事：
我需要使用seektables对flac文件进行编码，
-: 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 -
这似乎对我有用，并且产生的音频长度正确（在我的情况下-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 out.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
此
-: WARNING: skipping unknown chunk 'LIST' (use --keep-foreign-metadata to keep)
无法帮助：
ERROR: --keep-foreign-metadata cannot be used when encoding from stdin or to stdout
但是，即使我得到了
-: WARNING: unexpected EOF; expected 1073741823 samples, got 141516800 samples
这就是为什么它停止在13％（141516800 * 100/1073741823 = 13.2％）的原因，输出看起来很好，并且长度与输入相同！
更新：
发生这种情况是因为ffmpeg未填充输出wav的正确ChunkSize值，因为它被发送到管道而不是文件，因此ffmpeg最初使用4个0xFF字节作为ChunkSize到wav编码完成时，ffmpeg知道正确的值是什么，但无法回溯到输出管道中以更新ChunkSize部分。当输出到文件时，就可以。
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).
与将文件输出到管道时相比，ffmpeg wav输出到文件时的区别如下：
（注意：请勿运行此命令，即使在快速处理器上，也将花费几分钟的时间来占用100％的CPU，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 |................|
-----------
a。生成管道式的wav：ffmpeg -nostdin -i ~/audio/asmr/ASMR\ _\ Camera\ Touching\ _\ No\ Mouthsounds\ _\ NO\ TALKING-lQlZJ82ebBk.m4a -f wav - > piped.wav
b。用管道将其输送至：
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为0xFFFFFFFF）
a。将WAV生成到文件中：ffmpeg -nostdin -i ~/audio/asmr/ASMR\ _\ Camera\ Touching\ _\ No\ Mouthsounds\ _\ NO\ TALKING-lQlZJ82ebBk.m4a -f wav toafile.wav
b。用管道将其输送到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
这是因为它正确设置了ChunkSize值。 （ChunkSize为0x21BDC046 = 566,083,654，这比输出infile.wav少8个字节，该文件的总大小为566,083,662字节）