Maestro audio framework

Introduction

Maestro audio framework intends to enable chaining of basic audio processing blocks, called elements. These blocks then form stream processing objects, called pipeline. This pipeline can be used for multiple audio processing use cases.

The processing blocks can include (but are not limited to) different audio sources (for example file or microphone), decoders or encoders, filters or effects, and audio sinks. Framework overview is depicted in the following picture:

*not all elements and libraries are supported in Zephyr port. For more information, see Maestro on Zephyr

The Maestro audio framework is an open-source component developed by NXP Semiconductors and released under the BSD-compatible license. It is running on RTOS (Zephyr or FreeRTOS), abstracted by OSA layer.

For detailed description of the audio Maestro framework, please refer to the programmer’s guide.

To see what is new, see changelog.

Maestro on Zephyr

Getting started guide and further information for Maestro on Zephyr may be found here.

Maestro on FreeRTOS

Maestro on FreeRTOS is supported in NXP’s SDK. To get started, see mcuxsdk doc.

Supported examples

The current version of the Maestro audio framework supports several optional features, some of which are used in these examples:

• maestro_playback

• maestro_record

• maestro_usb_mic

• maestro_usb_speaker

• maestro_sync

The examples can be found in the audio_examples folder of the desired board. The demo applications are based on FreeRTOS and use multiple tasks to form the application functionality.

Example applications overview

To set up the audio framework properly, it is necessary to create a streamer with streamer_create API. It is also essential to set up the desired hardware peripherals using the functions described in streamer_pcm.h. The Maestro example projects consist of several files regarding the audio framework. The initial file is main.c with code to create multiple tasks. For features including SD card (in the maestro_playback examples, reading a file from SD card is supported and in maestro_record writing to SD card is currently supported) the APP_SDCARD_Task is created. The command prompt and connected functionalities are handled by APP_Shell_Task.

One of the most important parts of the configuration is the streamer_pcm.c where the initialization of the hardware peripherals, input and output buffer management can be found. For further information please see also streamer_pcm.h

In the Maestro USB examples (maestro_usb_mic and maestro_usb_speaker), the USB configuration is located in the usb_device_descriptor.c, audio_microphone.c and audio_speaker.c files. For further information please see also usb_device_descriptor.h, audio_microphone.h and audio_speaker.h.

In order to be able to get the messages from the audio framework, it is necessary to create a thread for receiving the messages from the streamer, which is usually called a Message Task. The message thread is placed in the app_streamer.c file, reads the streamer message queue, and reacts to the following messages:

• STREAM_MSG_ERROR - stops the streamer and exits the message thread

• STREAM_MSG_EOS - stops the streamer and exits the message thread

• STREAM_MSG_UPDATE_DURATION - prints info about the stream duration

• STREAM_MSG_UPDATE_POSITION - prints info about current stream position

• STREAM_MSG_CLOSE_TASK - exits the message thread

File structure

Folder	Description
src	Maestro audio framework sources
src/inc	Maestro include files
src/core	Maestro core sources
src/cci	Common decoder interface sources
src/cei	Common encoder interface sources
src/elements	Maestro elements sources
src/devices	External audio devices implementation (audio source & audio sink elements)
src/utils	Helper utilities utilized by Maestro
docs	Generated documentation
doxygen	Documentation sources
components	Glue for audio libraries, so they can be used in elements
tests	Maestro tests
zephyr/	Zephyr related files
zephyr/samples/	Zephyr samples
zephyr/tests/	Zephyr tests
zephyr/audioTracks/	Audio tracks for testing
zephyr/wrappers/	Zephyr NXP SDK Wrappers
zephyr/doc/	Zephyr documentation configuration for Sphinx
zephyr/scripts/	Zephyr helper scripts, mostly for testing

Contribution to the Maestro project

We welcome and encourage the community to submit patches directly to the Maestro project placed on github. Contributing can be managed via pull-requests.