如何解决使用FFmpeg的文件mp3串联问题
我想使用FFmpeg concatenation protocol连接一些MP3文件。
这是一次成功的尝试：
$ ffmpeg -loglevel panic -i "concat:audio/it/ci.mp3|audio/it/èsse.mp3|audio/it/cu.mp3|audio/it/u.mp3|audio/it/tre.mp3|audio/it/zero.mp3|audio/it/cinque.mp3|audio/it/quattro.mp3|audio/it/tre.mp3|audio/it/otto.mp3|audio/it/tre.mp3" -c copy audio/it/CSQU3054383.mp3 -y
$ ll audio/it/CSQU3054383.mp3
-rw-rw-r-- 1 giorgio 26K Nov 9 16:16 audio/it/CSQU3054383.mp3
到目前为止，一切都很好！
顺便说一句，所有（Mp3）文件都具有相同的编解码器，因此MP3 FFmpeg串联协议可以按预期运行！
现在，我想在每个先前的文件之间插入一个暂停文件audio/it/PAUSE_2.mp3：
$ ffmpeg -loglevel panic -i "concat:audio/it/ci.mp3|audio/it/PAUSE_2.mp3|audio/it/èsse.mp3|audio/it/PAUSE_2.mp3|audio/it/cu.mp3|audio/it/PAUSE_2.mp3|audio/it/u.mp3|audio/it/PAUSE_2.mp3|audio/it/tre.mp3|audio/it/PAUSE_2.mp3|audio/it/zero.mp3|audio/it/PAUSE_2.mp3|audio/it/cinque.mp3|audio/it/PAUSE_2.mp3|audio/it/quattro.mp3|audio/it/PAUSE_2.mp3|audio/it/tre.mp3|audio/it/PAUSE_2.mp3|audio/it/otto.mp3|audio/it/PAUSE_2.mp3|audio/it/tre.mp3" -c copy audio/it/CSQU3054383.mp3 -y
$
该命令运行显然没有任何错误，但是根本没有生成输出文件（audio/it/CSQU3054383.mp3）。
**问题1（未成年人）：
为什么FFmpeg不报告任何错误并且不生成预期的输出？**
事实上，在某些情况下，我已经经历过FFmpeg失败而未说出原因的原因：（
我怀疑问题是由于文件audio/it/PAUSE_2.mp3的比特率（CBR）和其他文件不同，例如：
$ mediainfo audio/it/ci.mp3
General
Complete name : audio/it/ci.mp3
Format : MPEG Audio
File size : 2.06 KiB
Duration : 528 ms
Overall bit rate mode : Constant
Overall bit rate : 32.0 kb/s
Audio
Format : MPEG Audio
Format version : Version 2
Format profile : Layer 3
Duration : 528 ms
Bit rate mode : Constant
Bit rate : 32.0 kb/s
Channel(s) : 1 channel
Sampling rate : 24.0 kHz
Frame rate : 41.667 FPS (576 SPF)
Compression mode : Lossy
Stream size : 2.06 KiB (100%)
$ ffprobe audio/it/ci.mp3
ffprobe version 3.4.8-0ubuntu0.2 Copyright (c) 2007-2020 the FFmpeg developers
built with gcc 7 (Ubuntu 7.5.0-3ubuntu1~18.04)
configuration: --prefix=/usr --extra-version=0ubuntu0.2 --toolchain=hardened --libdir=/usr/lib/x86_64-linux-gnu --incdir=/usr/include/x86_64-linux-gnu --enable-gpl --disable-stripping --enable-avresample --enable-avisynth --enable-gnutls --enable-ladspa --enable-libass --enable-libbluray --enable-libbs2b --enable-libcaca --enable-libcdio --enable-libflite --enable-libfontconfig --enable-libfreetype --enable-libfribidi --enable-libgme --enable-libgsm --enable-libmp3lame --enable-libmysofa --enable-libopenjpeg --enable-libopenmpt --enable-libopus --enable-libpulse --enable-librubberband --enable-librsvg --enable-libshine --enable-libsnappy --enable-libsoxr --enable-libspeex --enable-libssh --enable-libtheora --enable-libtwolame --enable-libvorbis --enable-libvpx --enable-libwavpack --enable-libwebp --enable-libx265 --enable-libxml2 --enable-libxvid --enable-libzmq --enable-libzvbi --enable-omx --enable-openal --enable-opengl --enable-sdl2 --enable-libdc1394 --enable-libdrm --enable-libiec61883 --enable-chromaprint --enable-frei0r --enable-libopencv --enable-libx264 --enable-shared
libavutil 55. 78.100 / 55. 78.100
libavcodec 57.107.100 / 57.107.100
libavformat 57. 83.100 / 57. 83.100
libavdevice 57. 10.100 / 57. 10.100
libavfilter 6.107.100 / 6.107.100
libavresample 3. 7. 0 / 3. 7. 0
libswscale 4. 8.100 / 4. 8.100
libswresample 2. 9.100 / 2. 9.100
libpostproc 54. 7.100 / 54. 7.100
[mp3 @ 0x564491288080] Estimating duration from bitrate,this may be inaccurate
Input #0,mp3,from 'audio/it/ci.mp3':
Duration: 00:00:00.53,start: 0.000000,bitrate: 32 kb/s
Stream #0:0: Audio: mp3,24000 Hz,mono,s16p,32 kb/s
相反，插入的暂停文件具有可变的比特率，如mediainfo所述：
$ mediainfo audio/it/PAUSE_2.mp3
General
Complete name : audio/it/PAUSE_2.mp3
Format : MPEG Audio
File size : 8.29 KiB
Overall bit rate mode : Variable
Writing library : LAME3.100
Audio
Format : MPEG Audio
Format version : Version 2
Format profile : Layer 3
Bit rate mode : Variable
Channel(s) : 1 channel
Sampling rate : 24.0 kHz
Compression mode : Lossy
Stream size : 8.06 KiB (97%)
Writing library : LAME3.100
这是我用来生成暂停的Bash脚本：
$ cat com/pause
#!/bin/bash
# https://ffmpeg.org/ffmpeg-filters.html#toc-anullsrc
# https://ffmpeg.org/ffmpeg-utils.html#toc-Examples-1
if [ $# -eq 0 ]
then
echo
echo "create a pause,a silence audio file (MP3) of specified number of milliseconds"
echo
echo "usage: $0 <time duration (in seconds)> <directory path>"
echo
echo "example: $0 2"
echo "example: $0 0.5 tmp/"
echo
exit
fi
timeDuration=$1
directoryPath=$2
suffix=mp3
# https://trac.ffmpeg.org/wiki/Limiting%20the%20output%20bitrate
#https://trac.ffmpeg.org/wiki/Encode/MP3
bitrate=32k
samplingRate=24000
outputFile="${directoryPath}PAUSE_${timeDuration}.${suffix}"
#-b:a $bitrate -minrate $bitrate -maxrate $bitrate -bufsize $bitrate \
ffmpeg \
-f lavfi \
-i anullsrc=r=$samplingRate:cl=mono \
-t $timeDuration \
-b:a $bitrate -minrate $bitrate -maxrate $bitrate \
-codec:a libmp3lame \
$outputFile -y
echo
echo "created file: $outputFile"
echo
不幸的是，所创建的文件似乎具有可变的比特率而不是恒定的比特率（CBR），如预期的那样（-b：a ...）：
$ com/pause 2
ffmpeg version 3.4.8-0ubuntu0.2 Copyright (c) 2000-2020 the FFmpeg developers
built with gcc 7 (Ubuntu 7.5.0-3ubuntu1~18.04)
configuration: --prefix=/usr --extra-version=0ubuntu0.2 --toolchain=hardened --libdir=/usr/lib/x86_64-linux-gnu --incdir=/usr/include/x86_64-linux-gnu --enable-gpl --disable-stripping --enable-avresample --enable-avisynth --enable-gnutls --enable-ladspa --enable-libass --enable-libbluray --enable-libbs2b --enable-libcaca --enable-libcdio --enable-libflite --enable-libfontconfig --enable-libfreetype --enable-libfribidi --enable-libgme --enable-libgsm --enable-libmp3lame --enable-libmysofa --enable-libopenjpeg --enable-libopenmpt --enable-libopus --enable-libpulse --enable-librubberband --enable-librsvg --enable-libshine --enable-libsnappy --enable-libsoxr --enable-libspeex --enable-libssh --enable-libtheora --enable-libtwolame --enable-libvorbis --enable-libvpx --enable-libwavpack --enable-libwebp --enable-libx265 --enable-libxml2 --enable-libxvid --enable-libzmq --enable-libzvbi --enable-omx --enable-openal --enable-opengl --enable-sdl2 --enable-libdc1394 --enable-libdrm --enable-libiec61883 --enable-chromaprint --enable-frei0r --enable-libopencv --enable-libx264 --enable-shared
libavutil 55. 78.100 / 55. 78.100
libavcodec 57.107.100 / 57.107.100
libavformat 57. 83.100 / 57. 83.100
libavdevice 57. 10.100 / 57. 10.100
libavfilter 6.107.100 / 6.107.100
libavresample 3. 7. 0 / 3. 7. 0
libswscale 4. 8.100 / 4. 8.100
libswresample 2. 9.100 / 2. 9.100
libpostproc 54. 7.100 / 54. 7.100
Input #0,lavfi,from 'anullsrc=r=24000:cl=mono':
Duration: N/A,bitrate: 192 kb/s
Stream #0:0: Audio: pcm_u8,u8,192 kb/s
Stream mapping:
Stream #0:0 -> #0:0 (pcm_u8 (native) -> mp3 (libmp3lame))
Press [q] to stop,[?] for help
Output #0,to 'PAUSE_2.mp3':
Metadata:
TSSE : Lavf57.83.100
Stream #0:0: Audio: mp3 (libmp3lame),32 kb/s
Metadata:
encoder : Lavc57.107.100 libmp3lame
size= 8kB time=00:00:02.01 bitrate= 33.7kbits/s speed= 192x
video:0kB audio:8kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: 2.870640%
created file: PAUSE_2.mp3
问题2：
我的Bash脚本有什么问题（为什么它不生成CBR文件？ 如何使用先前文件的确切设置生成一个静默暂停文件（N毫秒的静默）？
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