Raspberry Pi(樹莓派)聲音輸出可以設置為自動，耳機輸出，從HDMI輸出三種，默認為自動
pi@aborn ~ $ sudo apt-get install alsa-utils
pi@aborn ~ $ sudo modprobe snd-bcm2835 #把聲音模塊加入內核
pi@aborn ~ $ sudo aplay /usr/share/sounds/alsa/Front_Center.wav
pi@aborn /opt/vc $ sudo amixer cset numid=3 2
numid=3,iface=MIXER,name='PCM Playback Route'
; type=INTEGER,access=rw------,values=1,min=0,max=2,step=0
: values=2
pi@aborn /opt/vc $ sudo aplay /usr/share/sounds/alsa/Front_Center.wav
Playing WAVE '/usr/share/sounds/alsa/Front_Center.wav' : Signed 16 bit Little Endian, Rate 48000 Hz, Mono
pi@aborn /opt/vc $ sudo amixer cset numid=3
numid=3,iface=MIXER,name='PCM Playback Route'
; type=INTEGER,access=rw------,values=1,min=0,max=2,step=0
: values=0
pi@aborn /opt/vc $ sudo amixer cset numid=3 1
numid=3,iface=MIXER,name='PCM Playback Route'
; type=INTEGER,access=rw------,values=1,min=0,max=2,step=0
: values=1
values取不同的值分別代表：
0=auto(自動), 1=headphones(耳機), 2=hdmi
我發現播放視頻的時候非常消耗cpu資源
參考：http://raspberrypi.stackexchange.com/questions/44/why-is-my-audio-sound-output-not-working
