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DAC+ simultaneous playback

Sebastian Bauhaus

September 02, 2014 17:05

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Hi!

I followed the manual to install the Hifiberry dac+ on a Raspberry Pi B+ and it works well, I am able to play a mp3 file with mplayer, sounds great :-)

I now have the problem that I am not able to open two instances of mplayer at the same time, the error "[AO_ALSA] alsa-lib: pcm_hw.c:1293:(snd_pcm_hw_open) open '/dev/snd/pcmC0D0p' failed (-16): Device or resource busy" occurs.

If i wait until the first mplayer instance finished playing the other instance runs without a problem.
I understand that the Hifiberry does not include a hardware mixer so the man pages of ALSA told me that it will automatically activate dmix, does this work with the Hifiberry?

My (custom) program uses Qt with GStreamer, but I am testing with mplayer to get closer to the issue.

My /etc/asound.conf:

pcm.!default {
type hw
card 0
}

ctl.!default {
type hw
card 0
}

My aplay -l:

**** List of PLAYBACK Hardware Devices ****
card 0: sndrpihifiberry [snd_rpi_hifiberry_dacplus], device 0: HiFiBerry DAC+ HiFi pcm512x-hifi-0 []
Subdevices: 1/1
Subdevice #0: subdevice #0

My aplay -L:

null
Discard all samples (playback) or generate zero samples (capture)
sysdefault:CARD=sndrpihifiberry
snd_rpi_hifiberry_dacplus,
Default Audio Device

My OS:

Raspbian GNU/Linux 7

Thank you in advance!

Sebastian

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8 comments

• 0
  
  HiFiBerry team September 02, 2014 18:47

  Hi Sebastien,
  
  the driver on the Raspberry that is used for I2S sound cards does not support mixing sound from different applications. Only one application can use the card at a time. If you need this mixing functionality you might use pulseaudio to create a virtual sound card.
  
  Best regards
  Daniel
• 0
  
  Sebastian Bauhaus September 03, 2014 06:18

  Hi Daniel,
  
  thank you, Pulseaudio did the trick!
  
  Greetings
  Sebastian
• 0
  
  Frank Diehl April 23, 2015 07:28

  Hey,
  does this also apply to the Raspberry Pi 2?
  I want to use shairport sync and Kodi simultaniously because the airplay implementation of kodi doesnt sync the audio.
  But Shairport sync does not support pulseaudio so this is not an option
  
  Greetings
• 0
  
  HiFiBerry team April 23, 2015 09:25

  Hi Frank,
  
  the audio software stack is exactly the same on The RPI2. With Pulseaudio you can create a virtual sound card that can be used with shairport.
  
  Best regards
  Daniel
• 0
  
  Giles Thomas August 19, 2015 22:10

  Hi there -- I've been looking around the Internet for some kind of instructions on how to set up a virtual sound card using Pulseaudio, but I've struck out. Do you have any links?
• 0
  
  Giles Thomas August 19, 2015 22:56

  Also, do you think Dmix might do the job equally well? Pulseaudio looks a bit heavyweight just to get two apps using the card.
  
  Just as background -- I'm trying to get gmediarenderer-resurrect and shairport-sync working with a DAC+ on a Raspberry Pi 2, running the most recent Raspbian. Right now, they both work but once I've played something back with one of them, it holds on to the sound card and won't let go, so the other doesn't work until I've restarted the one that's holding on to the sound card.
• 0
  
  HiFiBerry team August 20, 2015 04:39

  You can try DMIX, we haven't done this before. I think it needs memory mapped IO which is not enabled by default. You need to enable it by a device tree overlay, but I can't say, if this is really working. It was buggy in the beginning and therefore was disabled by the developer.
  Here is a guide how to configure Pulseaudio:
  http://www.crazy-audio.com/2014/09/pulseaudio-on-the-raspbery-pi/
  
  Best regards
  Daniel
• 0
  
  Giles Thomas August 23, 2015 22:33

  Thanks! Sounds like I should go for Pulseaudio then. I'll try that now.