FireSound

Volume control for USB Audio devices on Amazon Fire TV

Motivation

The [Fire TV][0] outputs the audio signal along to the video signal over [HDMI][1] by default. Therefore, if a display is used which does not support audio over HDMI, such as a computer monitor, there won't be any sound. [0]: https://en.wikipedia.org/wiki/Amazon_Fire_TV [1]: https://en.wikipedia.org/wiki/HDMI

On the other hand, the Fire TV box offers a [USB][2] port which can be used for external audio devices, such as speakers or head phones. Luckily, the [Android][3] based software which runs on the Fire TV ([Fire OS][4]) supports audio output via USB, but with a snag: The is no user interface for volume control. The default output of digital audio via HDMI does not need (or support?) any volume control, respectively mixing. [2]: https://en.wikipedia.org/wiki/USB [3]: https://en.wikipedia.org/wiki/Android_(operating_system) [4]: https://en.wikipedia.org/wiki/Fire_OS

Description

There is one script listen_fireremote.sh which listens for Fire TV Remote events. Button presses of UP or DOWN while holding the MENU button increases or decreases the volume.

Another script listen_soundbar.sh listens for wheel events of the Dell AC511 SoundBar in order to increase or decrease the volume.

Currently, volume control is supported for USB audio devices only. HDMI is not supported because the author does not have access to an HDMI receiver with audio support for testing.

This volume control is carried out on a rather low level of the system and is expected to work everywhere, across all apps.

Requirements

Disclaimer

As usual, please be careful: these scripts run as root with nearly maximum privileges and thus might break your Fire TV! They work for the author but might fail elsewhere. Make sure to review the code before running it.

Installation

Get the latest release package.
Extract it to a path somewhere in /data/media/0 on your Fire TV box.
Set up one or both of the event listening scripts to be started at boot time with superuser permissions as shown below: (screenshots of a German Fire TV localization)

Implementation

The underlying Android system is based on a minimal Linux which supports audio mixing via the [tinyALSA][5] tools. Specifically on Android, tinymix can be used for this purpose. [5]: https://github.com/tinyalsa/tinyalsa

The script collection at hand uses the tinymix program to find an audio device which provides a linear playback volume mixer control.

Additionally, it sets up a background process querying the getevent builtin command for certain user input events, for example from the Fire TV Remote or another USB device. This in turn, is used to control the initially determined playback volume via tinymix.

Providing an arbitrary argument to the listener scripts listen_fireremote.sh or listen_soundbar.sh keeps them in the foreground and outputs debug information for each input event. Otherwise, during normal operation a log file is created in the log subdirectory of the scripts directory: firesound/log.

Licensing

This tool is available under the terms of the GPLv3. Please see the included LICENSE file for details.

ibressler/firesound