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QNX Software Development Platform
QNX SDP is a cross-compiling and debugging environment, including an IDE and command-line tools, for building binary images and programs for target boards running QNX Neutrino 7.1.
Audio & Graphics API
Audio Developer's Guide
The Audio Developer's Guide is intended for developers who want to write audio applications using the QNX Sound Architecture (QSA) drivers and library.
Playing and Capturing Audio Data
This chapter describes the major steps required to play back and capture (i.e., record) sound data.
Handling PCM devices
The software processes for playing back and capturing audio data are similar. This section describes the common steps.
Preparing the PCM subchannel
The next step in playing back or capturing the sound stream is to prepare the allocated subchannel to run.

QNX Momentics IDE User's Guide
This User's Guide describes version 7.1 of the Integrated Development Environment (IDE) that's part of the QNX Momentics tool suite.
QNX Software Development Platform
QNX SDP is a cross-compiling and debugging environment, including an IDE and command-line tools, for building binary images and programs for target boards running QNX Neutrino 7.1.
- Quickstart Guide
- OS Components & Operations
- Audio & Graphics API
  - Audio Developer's Guide
    The Audio Developer's Guide is intended for developers who want to write audio applications using the QNX Sound Architecture (QSA) drivers and library.
    - Audio Architecture
      This chapter includes information about QNX Sound Architecture (QSA), sounds cards and devices, sound card control devices, mixers, and pulse code modulation (PCM).
    - Playing and Capturing Audio Data
      This chapter describes the major steps required to play back and capture (i.e., record) sound data.
      - Handling PCM devices
        The software processes for playing back and capturing audio data are similar. This section describes the common steps.
        Opening your PCM device
        The first thing you need to do in order to play back or capture sound is open a connection to a PCM playback or capture device.
        Configuring the PCM device
        The next step in playing back or capturing the sound stream is to inform the device of the format of the data that you're about to send it or want to receive from it.
        Controlling voice conversion
        Configuration of the libasound library is based on the maximum number of voices supported in hardware.
        Preparing the PCM subchannel
        The next step in playing back or capturing the sound stream is to prepare the allocated subchannel to run.
        Closing the PCM subchannel
        When you've finished playing back or capturing audio data, you can close the subchannel by calling snd_pcm_close().
      - Playing audio data
        Once you've opened and configured a PCM playback device and prepared the PCM subchannel, you're ready to play back sound data.
      - Capturing audio data
        Once you've opened and configured a PCM capture device and prepared the PCM subchannel, you're ready to capture sound data.
    - Mixer Architecture
      This section describes the mixer architecture.
    - Audio Concurrency Management
      You can manage multiple audio streams using various audio policies.
    - Optimizing Audio
      Here are some tips for reducing audio latency:
    - Audio Library
      This chapter describes all of the supported QNX Sound Architecture (QSA) API functions, in alphabetical order; undocumented calls aren't supported.
    - afm_ctl.c example
      This is the source for the afm_ctl utility.
    - apx_ctl.c example
      This is the source for the apx_ctl utility.
    - wave.c example
      This is a sample application that plays back audio data.
    - waverec.c example
      This is a sample application that captures (i.e., records) audio data.
    - mix_ctl.c example
      This is a sample application that captures the groups and switches in the mixer.
    - audiomgmt_monitor.c example
      This is a sample application shows how to get the current active audio types.
    - ALSA and libasound.so
      The only supported interface to the ALSA 5 drivers is through libasound.so. Direct use of ioctl() commands isn't supported because of the requirements of the ALSA API. It uses ioctl() commands in ways that are illegal in the QNX Neutrino RTOS (e.g., passing a structure that contains a pointer through an ioctl()).
    - Glossary
  - Gestures Library Reference
    The Gestures library provides gesture recognizers to detect gestures through touch events that occur when you place one or more fingers on a touch screen.
  - Image Library Reference
  - Input Events Library Reference
    The Input Events library provides the framework necessary for Screen Graphics Subsystem to communicate with your touch driver.
  - OpenWF Configuration Developer's Guide
    If you are integrating a new display, you must configure and provide the parameters of your display based on its specifications via the OpenWF Display Configuration API (Wfdcfg Library).
  - Screen Graphics Subsystem Developer's Guide
    QNX Screen Graphics Subsystem is a graphics framework that provides all the functionality necessary to develop interactive user experiences.
  - Video Capture Developer's Guide
    The video capture framework provides applications the ability to capture frames from a video input source. These frames can be passed to a graphics component such as Screen for display.
- Multimedia
- Networking Middleware
- Programming
- Sensor Framework
- System Security Guide
  The QNX System Security Guide is intended for both system integrators who are responsible for the security of a QNX Neutrino RTOS system and developers who want to create a QNX Neutrino resource manager free from vulnerabilities.
- Utilities & Libraries
QNX Hypervisor
The QNX Hypervisor allows you to run multiple OSs on a target system so you can separate critical and non-critical functions, support a wide variety of applications, and reduce hardware costs.
QNX Software in the Cloud
QNX Software in the Cloud enables developers to use the QNX software in Amazon Web Services (AWS) and Microsoft Azure (Azure).
QNX Advanced Virtualization Frameworks User's Guide
This User's Guide is aimed at all systems integrators and developers who want to design and build embedded systems using the QNX Advanced Virtualization Frameworks.
Typographical Conventions, Support, and Licensing
This section describes the typographical conventions used throughout the documentation and explains how to obtain technical support.

Preparing the PCM subchannel

The next step in playing back or capturing the sound stream is to prepare the allocated subchannel to run.

Call one of the following functions to prepare the allocated subchannel:

snd_pcm_plugin_prepare() if you're using the plugin interface
snd_pcm_channel_prepare(), snd_pcm_capture_prepare(), or snd_pcm_playback_prepare() if you aren't
The snd_pcm_channel_prepare() function simply calls snd_pcm_capture_prepare() or snd_pcm_playback_prepare(), depending on the channel direction that you specify.

This step and the SND_PCM_STATUS_PREPARED state may seem unnecessary, but they're required to correctly handle underrun conditions when playing back, and overrun conditions when capturing. For more information, see If the PCM subchannel stops during playback and If the PCM subchannel stops during capture, later in this chapter.

Page updated: March 12, 2026