Hi,
I am trying to capture audio being played through ALSA on my Raspberry Pi.
I got the loopback device working (sending audio through it and
recording it on the other side):
```
maurus@raspy:~$ aplay -D loopback a2002011001-e02.wav
Playing WAVE 'a2002011001-e02.wav' : Signed 16 bit Little Endian, Rate
44100 Hz, Stereo
^CAborted by signal Interrupt...
maurus@raspy:~$ arecord -D loopback -f S16_LE -r 44100 -c 2 out.wav
Recording WAVE 'out.wav' : Signed 16 bit Little Endian, Rate 44100 Hz, Stereo
^CAborted by signal Interrupt...
maurus@raspy:~$ aplay -D tv out.wav
Playing WAVE 'out.wav' : Signed 16 bit Little Endian, Rate 44100 Hz, Stereo
^CAborted by signal Interrupt...
```
However when trying to play audio through a multi device, I get the
following error:
```
maurus@raspy:~$ aplay -D monitor a2002011001-e02.wav
Playing WAVE 'a2002011001-e02.wav' : Signed 16 bit Little Endian, Rate
44100 Hz, Stereo
aplay: pcm_params.c:170: snd1_pcm_hw_param_get_min: Assertion
`!snd_interval_empty(i)' failed.
Aborted by signal Aborted...
```
This is my config:
```
pcm.tv {
type plug
slave.pcm "plughw:CARD=ALSA,DEV=1"
}
pcm.loopback {
type plug
slave.pcm {
type asym
playback.pcm {
type dmix
ipc_key 1234
slave.pcm "hw:CARD=Loopback0,DEV=0"
}
capture.pcm {
type dsnoop
ipc_key 1235
slave.pcm "hw:CARD=Loopback0,DEV=1"
}
}
}
pcm.monitor {
type plug
slave.pcm {
type multi
slaves {
a { pcm "tv"; channels 2 }
b { pcm "loopback"; channels 2 }
}
bindings {
0 { slave a; channel 0 }
1 { slave a; channel 1 }
2 { slave b; channel 0 }
3 { slave b; channel 1 }
}
master 0
}
route_policy "duplicate"
# ttable {
# [1.0 0.0 1.0 0.0] # left -> a.left, b.left
# [0.0 1.0 0.0 1.0] # right -> a.right, b.right
# }
}
```
And this is my environment:
```
maurus@raspy:~$ lsb_release -a
No LSB modules are available.
Distributor ID: Ubuntu
Description: Ubuntu 15.10
Release: 15.10
Codename: wily
maurus@raspy:~$ apt-cache show alsa-base | fgrep Version
Version: 1.0.25+dfsg-0ubuntu5
maurus@raspy:~$ uname -a
Linux raspy 4.1.15-v7+ #830 SMP Tue Dec 15 17:02:45 GMT 2015 armv7l
armv7l armv7l GNU/Linux
maurus@raspy:~$ lsmod|fgrep snd
snd_aloop 12632 0
snd_bcm2835 19739 0
snd_pcm 75040 2 snd_bcm2835,snd_aloop
snd_timer 18668 1 snd_pcm
snd 52620 4 snd_bcm2835,snd_aloop,snd_timer,snd_pcm
maurus@raspy:~$ aplay -L
null
Discard all samples (playback) or generate zero samples (capture)
tv
loopback
monitor
default
sysdefault:CARD=ALSA
bcm2835 ALSA, bcm2835 ALSA
Default Audio Device
dmix:CARD=ALSA,DEV=0
bcm2835 ALSA, bcm2835 ALSA
Direct sample mixing device
dmix:CARD=ALSA,DEV=1
bcm2835 ALSA, bcm2835 IEC958/HDMI
Direct sample mixing device
dsnoop:CARD=ALSA,DEV=0
bcm2835 ALSA, bcm2835 ALSA
Direct sample snooping device
dsnoop:CARD=ALSA,DEV=1
bcm2835 ALSA, bcm2835 IEC958/HDMI
Direct sample snooping device
hw:CARD=ALSA,DEV=0
bcm2835 ALSA, bcm2835 ALSA
Direct hardware device without any conversions
hw:CARD=ALSA,DEV=1
bcm2835 ALSA, bcm2835 IEC958/HDMI
Direct hardware device without any conversions
plughw:CARD=ALSA,DEV=0
bcm2835 ALSA, bcm2835 ALSA
Hardware device with all software conversions
plughw:CARD=ALSA,DEV=1
bcm2835 ALSA, bcm2835 IEC958/HDMI
Hardware device with all software conversions
sysdefault:CARD=Loopback0
Loopback, Loopback PCM
Default Audio Device
front:CARD=Loopback0,DEV=0
Loopback, Loopback PCM
Front speakers
surround21:CARD=Loopback0,DEV=0
Loopback, Loopback PCM
2.1 Surround output to Front and Subwoofer speakers
surround40:CARD=Loopback0,DEV=0
Loopback, Loopback PCM
4.0 Surround output to Front and Rear speakers
surround41:CARD=Loopback0,DEV=0
Loopback, Loopback PCM
4.1 Surround output to Front, Rear and Subwoofer speakers
surround50:CARD=Loopback0,DEV=0
Loopback, Loopback PCM
5.0 Surround output to Front, Center and Rear speakers
surround51:CARD=Loopback0,DEV=0
Loopback, Loopback PCM
5.1 Surround output to Front, Center, Rear and Subwoofer speakers
surround71:CARD=Loopback0,DEV=0
Loopback, Loopback PCM
7.1 Surround output to Front, Center, Side, Rear and Woofer speakers
dmix:CARD=Loopback0,DEV=0
Loopback, Loopback PCM
Direct sample mixing device
dmix:CARD=Loopback0,DEV=1
Loopback, Loopback PCM
Direct sample mixing device
dsnoop:CARD=Loopback0,DEV=0
Loopback, Loopback PCM
Direct sample snooping device
dsnoop:CARD=Loopback0,DEV=1
Loopback, Loopback PCM
Direct sample snooping device
hw:CARD=Loopback0,DEV=0
Loopback, Loopback PCM
Direct hardware device without any conversions
hw:CARD=Loopback0,DEV=1
Loopback, Loopback PCM
Direct hardware device without any conversions
plughw:CARD=Loopback0,DEV=0
Loopback, Loopback PCM
Hardware device with all software conversions
plughw:CARD=Loopback0,DEV=1
Loopback, Loopback PCM
Hardware device with all software conversions
```
Does anyone have any clue how to get this config working?
Thanks,
--
Maurus Cuelenaere
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