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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.
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.
Stopping the playback
If the application wishes to stop playback, it can simply stop sending data and let the subchannel underrun as described above, but there are better ways.

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.
      - 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.
        Playback states
        Let's consider the state transitions for a PCM device during playback.
        Sending data to the PCM subchannel
        The function that you call to send data to the subchannel depends on whether or not you're using plugin converters.
        If the PCM subchannel stops during playback
        When playing back, the PCM subchannel stops if the hardware consumes all the data in its buffer.
        Stopping the playback
        If the application wishes to stop playback, it can simply stop sending data and let the subchannel underrun as described above, but there are better ways.
        Synchronizing with the PCM subchannel
        QSA provides some basic synchronization capabilities.
      - 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.

Stopping the playback

If the application wishes to stop playback, it can simply stop sending data and let the subchannel underrun as described above, but there are better ways.

If you want your application to stop as soon as possible, call one of the drop functions to discard any buffered data:

snd_pcm_plugin_drop() if you're using the plugins
snd_pcm_channel_drop() if you aren't

If you want to play out all data in the buffers before stopping, call one of:

snd_pcm_plugin_drain() if you're using the plugins
snd_pcm_channel_drain() if you aren't

The drain functions block until all buffered data is played out and the stream is stopped.

Page updated: March 12, 2026