为什么无法使用 PAREC 捕捉网络摄像头的声音？

Question

使用命令列出所有输入设备：

pactl list sources | grep -A 5 Source
Source #0
State: RUNNING
Name: alsa_input.usb-SN0002_HIK_1080P_CAMERA_SN0002-02.mono-fallback
Description: HIK 1080P CAMERA Mono
Driver: module-alsa-card.c
Sample Specification: s16le 1ch 16000Hz
--
Source #1
State: RUNNING
Name: alsa_output.pci-0000_09_00.6.analog-stereo.monitor
Description: Monitor of Family 17h (Models 10h-1fh) HD Audio Controller Analog Stereo
Driver: module-alsa-card.c
Sample Specification: s16le 2ch 44100Hz

用同样的方式捕获声卡上播放的音频：

parecord -d  alsa_output.pci-0000_09_00.6.analog-stereo.monitor  sample.wav

它工作得很好，现在可以用我的网络摄像头捕捉音频

arecord -d  alsa_input.usb-SN0002_HIK_1080P_CAMERA_SN0002-02.analog-mono-fallback sample.wav
Stream error: No such entity

显示 alsa_input 的状态：

pacmd dump | grep alsa_input
set-source-volume alsa_input.usb-SN0002_HIK_1080P_CAMERA_SN0002-02.mono-fallback 0x13220
set-source-mute alsa_input.usb-SN0002_HIK_1080P_CAMERA_SN0002-02.mono-fallback no
suspend-source alsa_input.usb-SN0002_HIK_1080P_CAMERA_SN0002-02.mono-fallback no
set-default-source alsa_input.usb-SN0002_HIK_1080P_CAMERA_SN0002-02.mono-fallback

状态良好，为什么我的网络摄像头无法捕捉到说话的声音？奇怪的是，可以使用 arecord 命令捕获对网络摄像头说话的音频：

#get the hardware info
arecord -L|grep  plughw|grep  CAMERA
plughw:CARD=CAMERA,DEV=0
#write the command  
arecord --device="plughw:CARD=CAMERA,DEV=0"  music.wav

为什么arecord可以捕获所有对网络摄像头说话的声音而不是parecord？