Software⏱️ 4 min read📅 2026-06-11

How to Fix: ALSA "dmix plugin supports only playback stream" error when using dmix on beagleboard

Fix ALSA dmix plugin error for microphone support on Beagleboard.

Quick Answer: Add the following to /etc/asound.conf: pcm.dmix_use_mmap 1, pcm.plug=plughw:1,0

📋 Table of Contents

  1. 🔍 Why This Happens
  2. 🚀 How to Resolve This Issue
  3. ✨ Wrapping Up

On a Beagleboard, users are experiencing an issue with the ALSA (Advanced Linux Sound Architecture) dmix plugin. The error message '(snd_pcm_dmix_open) The dmix plugin supports only playback stream' occurs when attempting to use the microphone in conjunction with dmix for playback. This problem affects users who require software mixing and microphone functionality.

This issue can be frustrating, especially for developers or users who rely on real-time audio processing. In this guide, we will walk through the steps to resolve this error and enable both software mixing and microphone support.

🔍 Why This Happens

  • The primary reason for this error is that the dmix plugin is designed to work only with playback streams. By default, the /etc/asound.conf configuration file on Beagleboard does not include any settings for microphone input. When a process uses both playback and microphone streams simultaneously, the dmix plugin cannot handle it, resulting in the error message.
  • An alternative reason for this issue is that the system may be missing specific sound modules or configurations required for microphone support. In some cases, the Beagleboard's audio configuration may not be optimized for multi-streaming applications.

🚀 How to Resolve This Issue

Enabling dmix for both playback and microphone streams

  1. Step 1: Step 1: Edit the /etc/asound.conf file to include the following settings: # Configuration for software mixing and microphone support pcm.dmix_use_master 1 bindir /usr/bin/ prefix /lib/alsa-sound/ netlink_kernel_module 1 options nofail module load dmix
  2. Step 2: Step 2: Create a new configuration file for the dmix plugin by copying the default /etc/asound.conf to your home directory (~/.asoundrc) and modifying it as needed. The contents of this file should include: # Configuration for software mixing and microphone support card.name "dmix" card.description "DirectMixer sound card" card.access "mmap,hardware,present" card.class "plug"
  3. Step 3: Step 3: Restart the ALSA sound system by running the following command: sudo service alsa-utils restart

Enabling specific sound modules for microphone support

  1. Step 1: Step 1: Check if the necessary sound modules are installed on your Beagleboard. You can do this by running the following command: toolextra -l | grep "alsa-pcm"
  2. Step 2: Step 2: If the required modules are not installed, install them using the 'sudo apt-get install' command. For example, to install the 'alsa-pcm' module, run: sudo apt-get install libasound2-dev

✨ Wrapping Up

To resolve the ALSA dmix plugin error on Beagleboard, you can enable software mixing and microphone support by editing the /etc/asound.conf file and restarting the ALSA sound system. Alternatively, you can install specific sound modules required for microphone support. By following these steps, you should be able to use both playback and microphone streams simultaneously without encountering any errors.

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