对于大多数设备来说，都有一个原始版本/dev。
/dev/video0对于视频设备，有/dev/video、等。
/dev/tty1对于终端，有/dev/tty2、等。
/dev/sda对于存储设备，有/dev/sdb、等。
以前有一个/dev/dsp用于声音设备的。但是，现在不存在了。
有人能告诉我用于与原始设备接口的声音设备等效的东西吗？
我花了很多时间研究/dev子目录的内容。我无法识别代表声音设备的项目，也无法识别要尝试连接的设备。
这一个记录命令显示这些可用的声音设备：
$ arecord -l
**** List of CAPTURE Hardware Devices ****
card 0: MID [HDA Intel MID], device 0: ALC889A Analog [ALC889A Analog]
Subdevices: 0/1
Subdevice #0: subdevice #0
card 0: MID [HDA Intel MID], device 2: ALC889A Alt Analog [ALC889A Alt Analog]
Subdevices: 2/2
Subdevice #0: subdevice #0
Subdevice #1: subdevice #1
card 2: HDMI [USB Capture HDMI], device 0: USB Audio [USB Audio]
Subdevices: 0/1
Subdevice #0: subdevice #0
card 3: C525 [HD Webcam C525], device 0: USB Audio [USB Audio]
Subdevices: 0/1
Subdevice #0: subdevice #0
有没有办法解释这些信息并使用它来捕获来自任何或所有设备的音频。
我可以用什么命令来替代其他命令来使用 ffmpeg 命令（例如用于捕获的这些命令）？
$ ffmpeg -f alsa -i /dev/dsp out.wav
$ ffmpeg -f alsa -i hw:2 -t 30 out.wav
arecord -l未运行的输出pavucontrol：
$ arecord -l
**** List of CAPTURE Hardware Devices ****
card 0: MID [HDA Intel MID], device 0: ALC889A Analog [ALC889A Analog]
Subdevices: 1/1
Subdevice #0: subdevice #0
card 0: MID [HDA Intel MID], device 2: ALC889A Alt Analog [ALC889A Alt Analog]
Subdevices: 2/2
Subdevice #0: subdevice #0
Subdevice #1: subdevice #1
card 2: HDMI [USB Capture HDMI], device 0: USB Audio [USB Audio]
Subdevices: 1/1
Subdevice #0: subdevice #0
card 3: C525 [HD Webcam C525], device 0: USB Audio [USB Audio]
Subdevices: 1/1
Subdevice #0: subdevice #0
根据评论中的信息进行更新
此命令会生成一个 30 秒的文件，其中的声音来自我的 USB HDMI 采集卡：
$ ffmpeg -f alsa -i hw:2 -t 30 out.wav
ffmpeg version 2.8.11-0ubuntu0.16.04.1 Copyright (c) 2000-2017 the FFmpeg developers
built with gcc 5.4.0 (Ubuntu 5.4.0-6ubuntu1~16.04.4) 20160609
configuration: --prefix=/usr --extra-version=0ubuntu0.16.04.1 --build-suffix=-ffmpeg --toolchain=hardened --libdir=/usr/lib/x86_64-linux-gnu --incdir=/usr/include/x86_64-linux-gnu --cc=cc --cxx=g++ --enable-gpl --enable-shared --disable-stripping --disable-decoder=libopenjpeg --disable-decoder=libschroedinger --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-libmodplug --enable-libmp3lame --enable-libopenjpeg --enable-libopus --enable-libpulse --enable-librtmp --enable-libschroedinger --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-libxvid --enable-libzvbi --enable-openal --enable-opengl --enable-x11grab --enable-libdc1394 --enable-libiec61883 --enable-libzmq --enable-frei0r --enable-libx264 --enable-libopencv
WARNING: library configuration mismatch
avcodec configuration: --prefix=/usr --extra-version=0ubuntu0.16.04.1 --build-suffix=-ffmpeg --toolchain=hardened --libdir=/usr/lib/x86_64-linux-gnu --incdir=/usr/include/x86_64-linux-gnu --cc=cc --cxx=g++ --enable-gpl --enable-shared --disable-stripping --disable-decoder=libopenjpeg --disable-decoder=libschroedinger --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-libmodplug --enable-libmp3lame --enable-libopenjpeg --enable-libopus --enable-libpulse --enable-librtmp --enable-libschroedinger --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-libxvid --enable-libzvbi --enable-openal --enable-opengl --enable-x11grab --enable-libdc1394 --enable-libiec61883 --enable-libzmq --enable-frei0r --enable-libx264 --enable-libopencv --enable-version3 --disable-doc --disable-programs --disable-avdevice --disable-avfilter --disable-avformat --disable-avresample --disable-postproc --disable-swscale --enable-libopencore_amrnb --enable-libopencore_amrwb --enable-libvo_aacenc --enable-libvo_amrwbenc
libavutil 54. 31.100 / 54. 31.100
libavcodec 56. 60.100 / 56. 60.100
libavformat 56. 40.101 / 56. 40.101
libavdevice 56. 4.100 / 56. 4.100
libavfilter 5. 40.101 / 5. 40.101
libavresample 2. 1. 0 / 2. 1. 0
libswscale 3. 1.101 / 3. 1.101
libswresample 1. 2.101 / 1. 2.101
libpostproc 53. 3.100 / 53. 3.100
Guessed Channel Layout for Input Stream #0.0 : stereo
Input #0, alsa, from 'hw:2':
Duration: N/A, start: 1513743504.091042, bitrate: 1536 kb/s
Stream #0:0: Audio: pcm_s16le, 48000 Hz, 2 channels, s16, 1536 kb/s
Output #0, wav, to 'out.wav':
Metadata:
ISFT : Lavf56.40.101
Stream #0:0: Audio: pcm_s16le ([1][0][0][0] / 0x0001), 48000 Hz, stereo, s16, 1536 kb/s
Metadata:
encoder : Lavc56.60.100 pcm_s16le
Stream mapping:
Stream #0:0 -> #0:0 (pcm_s16le (native) -> pcm_s16le (native))
Press [q] to stop, [?] for help
size= 5621kB time=00:00:30.00 bitrate=1535.0kbits/s
video:0kB audio:5621kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: 0.001355%
当尝试从我的网络摄像头麦克风捕获声音时，此命令产生以下错误：
（错误是输出的最后两行。）
$ ffmpeg -f alsa -i hw:3 -t 30 out.wav
ffmpeg version 2.8.11-0ubuntu0.16.04.1 Copyright (c) 2000-2017 the FFmpeg developers
built with gcc 5.4.0 (Ubuntu 5.4.0-6ubuntu1~16.04.4) 20160609
configuration: --prefix=/usr --extra-version=0ubuntu0.16.04.1 --build-suffix=-ffmpeg --toolchain=hardened --libdir=/usr/lib/x86_64-linux-gnu --incdir=/usr/include/x86_64-linux-gnu --cc=cc --cxx=g++ --enable-gpl --enable-shared --disable-stripping --disable-decoder=libopenjpeg --disable-decoder=libschroedinger --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-libmodplug --enable-libmp3lame --enable-libopenjpeg --enable-libopus --enable-libpulse --enable-librtmp --enable-libschroedinger --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-libxvid --enable-libzvbi --enable-openal --enable-opengl --enable-x11grab --enable-libdc1394 --enable-libiec61883 --enable-libzmq --enable-frei0r --enable-libx264 --enable-libopencv
WARNING: library configuration mismatch
avcodec configuration: --prefix=/usr --extra-version=0ubuntu0.16.04.1 --build-suffix=-ffmpeg --toolchain=hardened --libdir=/usr/lib/x86_64-linux-gnu --incdir=/usr/include/x86_64-linux-gnu --cc=cc --cxx=g++ --enable-gpl --enable-shared --disable-stripping --disable-decoder=libopenjpeg --disable-decoder=libschroedinger --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-libmodplug --enable-libmp3lame --enable-libopenjpeg --enable-libopus --enable-libpulse --enable-librtmp --enable-libschroedinger --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-libxvid --enable-libzvbi --enable-openal --enable-opengl --enable-x11grab --enable-libdc1394 --enable-libiec61883 --enable-libzmq --enable-frei0r --enable-libx264 --enable-libopencv --enable-version3 --disable-doc --disable-programs --disable-avdevice --disable-avfilter --disable-avformat --disable-avresample --disable-postproc --disable-swscale --enable-libopencore_amrnb --enable-libopencore_amrwb --enable-libvo_aacenc --enable-libvo_amrwbenc
libavutil 54. 31.100 / 54. 31.100
libavcodec 56. 60.100 / 56. 60.100
libavformat 56. 40.101 / 56. 40.101
libavdevice 56. 4.100 / 56. 4.100
libavfilter 5. 40.101 / 5. 40.101
libavresample 2. 1. 0 / 2. 1. 0
libswscale 3. 1.101 / 3. 1.101
libswresample 1. 2.101 / 1. 2.101
libpostproc 53. 3.100 / 53. 3.100
[alsa @ 0x17c7f80] cannot set channel count to 2 (Invalid argument)
hw:3: Input/output error
此命令（arecord -L使用这个答案，运行无错误：
$ ffmpeg -f alsa -i plughw:CARD=C525,DEV=0 -t 30 out.wav
ffmpeg version 2.8.11-0ubuntu0.16.04.1 Copyright (c) 2000-2017 the FFmpeg developers
built with gcc 5.4.0 (Ubuntu 5.4.0-6ubuntu1~16.04.4) 20160609
configuration: --prefix=/usr --extra-version=0ubuntu0.16.04.1 --build-suffix=-ffmpeg --toolchain=hardened --libdir=/usr/lib/x86_64-linux-gnu --incdir=/usr/include/x86_64-linux-gnu --cc=cc --cxx=g++ --enable-gpl --enable-shared --disable-stripping --disable-decoder=libopenjpeg --disable-decoder=libschroedinger --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-libmodplug --enable-libmp3lame --enable-libopenjpeg --enable-libopus --enable-libpulse --enable-librtmp --enable-libschroedinger --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-libxvid --enable-libzvbi --enable-openal --enable-opengl --enable-x11grab --enable-libdc1394 --enable-libiec61883 --enable-libzmq --enable-frei0r --enable-libx264 --enable-libopencv
WARNING: library configuration mismatch
avcodec configuration: --prefix=/usr --extra-version=0ubuntu0.16.04.1 --build-suffix=-ffmpeg --toolchain=hardened --libdir=/usr/lib/x86_64-linux-gnu --incdir=/usr/include/x86_64-linux-gnu --cc=cc --cxx=g++ --enable-gpl --enable-shared --disable-stripping --disable-decoder=libopenjpeg --disable-decoder=libschroedinger --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-libmodplug --enable-libmp3lame --enable-libopenjpeg --enable-libopus --enable-libpulse --enable-librtmp --enable-libschroedinger --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-libxvid --enable-libzvbi --enable-openal --enable-opengl --enable-x11grab --enable-libdc1394 --enable-libiec61883 --enable-libzmq --enable-frei0r --enable-libx264 --enable-libopencv --enable-version3 --disable-doc --disable-programs --disable-avdevice --disable-avfilter --disable-avformat --disable-avresample --disable-postproc --disable-swscale --enable-libopencore_amrnb --enable-libopencore_amrwb --enable-libvo_aacenc --enable-libvo_amrwbenc
libavutil 54. 31.100 / 54. 31.100
libavcodec 56. 60.100 / 56. 60.100
libavformat 56. 40.101 / 56. 40.101
libavdevice 56. 4.100 / 56. 4.100
libavfilter 5. 40.101 / 5. 40.101
libavresample 2. 1. 0 / 2. 1. 0
libswscale 3. 1.101 / 3. 1.101
libswresample 1. 2.101 / 1. 2.101
libpostproc 53. 3.100 / 53. 3.100
Guessed Channel Layout for Input Stream #0.0 : stereo
Input #0, alsa, from 'plughw:CARD=C525,DEV=0':
Duration: N/A, start: 1513743836.271555, bitrate: 1536 kb/s
Stream #0:0: Audio: pcm_s16le, 48000 Hz, 2 channels, s16, 1536 kb/s
Output #0, wav, to 'out.wav':
Metadata:
ISFT : Lavf56.40.101
Stream #0:0: Audio: pcm_s16le ([1][0][0][0] / 0x0001), 48000 Hz, stereo, s16, 1536 kb/s
Metadata:
encoder : Lavc56.60.100 pcm_s16le
Stream mapping:
Stream #0:0 -> #0:0 (pcm_s16le (native) -> pcm_s16le (native))
Press [q] to stop, [?] for help
size= 5625kB time=00:00:30.00 bitrate=1536.0kbits/s
video:0kB audio:5625kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: 0.001354%
尝试从网络摄像头获取声音的命令的其他变体包括（来自尼克·格诺米克的评论):
$ ffmpeg -f alsa -i hw:3,0 -t 30 out.wav
答案1
虽然可能还有其他工具可以提供音频设备，一个记录在 Ubuntu 16.04 中默认提供。
列出可用声音设备的命令是（我的情况下的命令和输出如下）：
$ arecord -l
**** List of CAPTURE Hardware Devices ****
card 0: MID [HDA Intel MID], device 0: ALC889A Analog [ALC889A Analog]
Subdevices: 1/1
Subdevice #0: subdevice #0
card 0: MID [HDA Intel MID], device 2: ALC889A Alt Analog [ALC889A Alt Analog]
Subdevices: 2/2
Subdevice #0: subdevice #0
Subdevice #1: subdevice #1
card 2: C525 [HD Webcam C525], device 0: USB Audio [USB Audio]
Subdevices: 1/1
Subdevice #0: subdevice #0
card 3: Microphone [Yeti Stereo Microphone], device 0: USB Audio [USB Audio]
Subdevices: 1/1
Subdevice #0: subdevice #0
card 4: HDMI [USB Capture HDMI], device 0: USB Audio [USB Audio]
Subdevices: 1/1
Subdevice #0: subdevice #0
在这种情况下，网络摄像头音频是硬件设备Card 2。ffmpeg在这种情况下是hw:2。
问题中的问题，根据错误输出，是在ffmpeg捕获程序的默认设置。它生成错误是cannot set channel count to 2 (Invalid argument)因为摄像头显然是使用音频通道 1 进行捕获，而捕获应用程序ffmpeg显然正试图从音频通道 2（这是 ffmpeg 的默认捕获通道）捕获。
从网络摄像头捕获音频可以通过 GUI 应用程序进行，因为它们显然具有一些捕获机制来识别输入的可用音频通道并从该通道中提取。
指定ffmpeg的捕获通道
要指定 ffmpeg 应用程序的捕获通道，请在参数-ac [channel #]之前使用-i。
对于问题中的命令进行以下更改：
更改自：
$ ffmpeg -f alsa -i hw:2 -t 30 out.wav
改成：
$ ffmpeg -f alsa -ac 1 -i hw:2 -t 30 out.wav
答案2
您似乎已经找到了可行的解决方案：
ffmpeg -f alsa -i plughw:CARD=C525,DEV=0 -t 30 out.wav
hw:CARD=C525,DEV=0比使用hw:3,0
USB 设备更好的选择可能分配不同的卡号
卡名，避免设备号码发生变化时可能出现的错误
plughw:是比hw:
plughw 更好的选择，可以处理任何采样率转换