AVS Device SDK Optional Features

This page provides extra information to help you implement optional AVS features with the Alexa Voice Service (AVS) Device SDK. For code samples and full implementation details, see the AVS Device SDK on GitHub or the AVS Device SDK API references.


This page isn't an exhaustive list of all SDK features available.


To enable Alerts, you must follow these instructions.

  1. Install SQLite.
  2. Set your device system clock to UTC time. To set UTC time, use Network Time Protocol (NTP).
  3. Install a file system.


Building with Bluetooth is optional and is supported on Linux or Raspberry Pi.


The Alexa Voice Service (AVS) Device SDK 1.17 adds support for captions.

In the SDK, it's disabled by default. You enable through the CMake build option CAPTIONS=ON. You must also install a new dependency – the libwebvtt parsing library. Webvtt is a C/C++ library for interpreting and authoring WebVTT content. WebVTT is a caption and subtitle format designed for use with HTML5 audio and video elements.

By default, captions works with the en-US locale. If you want to support another locale, you must modify the line break logic in the CaptionManager::onParsed() method and use a locale-safe method for determining the break points between words. For example, you can use the ICU BreakIterator to handle the task. The exact method of this implementation is determined by you.

To enable captions to your device

  1. Download and install webvt to a directory of your choice. If there are any additional instructions provided for your OS on the webvt page, make sure you follow them.
  2. Build the AVS Device SDK and configure your CMake command with the following flags

     -DLIBWEBVTT_LIB_PATH=$HOME/captions/webvtt-master/build/src/webvtt/libwebvtt.a \


For more details about enabling endpoints, see Smart Home Endpoints.

SAMPLE-AES decryption

SAMPLE-AES decryption is optional.

To enable SAMPLE-AES decryption for audio streamed to your device

  1. Install the FFMPEG library.
  2. Enable SAMPLE-AES decryption with the following CMake command.

     cmake [absolute path to source] -DENABLE_SAMPLE_AES[ON|OFF]     
                                     -DFFMPEG_LIB_PATH=[absolute path to ffmpeg library]
                                     -DFFMPEG_INCLUDE_DIR=[absolute path to ffmpeg include directory]

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Last updated: Sep 28, 2021