~ Decode MP3s and other Audio formats the easy way on Android

This post describes how to decode MP3’s using an already compiled ffmpeg binary on android. Using ffmpeg to decode audio on Android has advantages:

  • It supports about every audio format known to man. Three channel flac, vorbis with 32 bit samples, … do not pose a problem.
  • Extracting audio from video container formats is supported. Accessing the first audio stream from mkv, avi, mov,… just works.
  • Decoding audio frames is more efficient using native code than often buggy Java decoders.
  • Resampling and downmixing is supported. If you want to resample incoming audio to e.g. 44.1kHz and only want single channel audio this is easily achievable.

The main disadvantage is that you need an ffmpeg build for your Android device. Luckily some poor soul already managed to compile ffmeg for Android for several architectures. The precompiled ffmpeg binaries for Android are available for download and are mirrored here as well.

To bridge the ffmpeg binary and the java world TarsosDSP contains some glue code. The AndroidFFMPEGLocator is responsible to find and extract the correct binary for your Android device. It expects these ffmpeg binaries in the assets folder of your Android application. When the correct ffmpeg binary has been extracted and made executable the PipeDecoder is able to call it. The PipeDecoder calls ffmpeg so that decoded, downmixed and resampled PCM samples are streamed into the Java application via a pipe, which explains its name.

With the TarsosDSP Android library the following code plays an MP3 from external storage:

new AndroidFFMPEGLocator(this);
new Thread(new Runnable() {
  public void run() {
    File externalStorage = Environment.getExternalStorageDirectory();
    File mp3 = new File(externalStorage.getAbsolutePath() , "/audio.mp3");
    AudioDispatcher adp;
    adp = AudioDispatcherFactory.fromPipe(mp3.getAbsolutePath(),44100,5000,2500);
    adp.addAudioProcessor(new AndroidAudioPlayer(adp.getFormat(),5000, AudioManager.STREAM_MUSIC));

This code just works if the application has the READ_EXTERNAL_STORAGE permission, includes a recent TarsosDSP-Android.jar, is ran on one of the supported ffmpeg architectures and has these binaries available in the assets folder.

~ TeensyDAQ - Capture, Visualize and Record Analog Input Signals from Teensy

This post describes a tool to quickly visualize and record analog signals with a Teensy micro-controller and some custom software. It is mainly useful to quickly get an idea of how an analog sensor reacts to different stimuli. Since it is also able to capture and store analog input siginals it is also useful to generate test data recordings which then can be used for example to test a peak detection algorithm on. The tool is called TeensyDAQ hinting at the Data AcQuisition features and the micro-controller used.

Some of the features of the TeensyDAQ:

  • Visualize up to five analog signals simultaneously in real-time.
  • Capture analog input signals with sampling rates up to 8000Hz.
  • Record analog input to a CSV-file and, using drag-and-drop, previously recorded CSV-files can be visualized.
  • Works on Linux, Mac OS X and Windows.
  • While a capture session is in progress you can going back in time and zoom, pan and drag to get a detailed view on your data.
  • Allows you to listen to your input signal, this is especially practical with analog microphone input.

The system consists of two parts. A hardware and a software part. The hardware is a Teensy micro-controller running an Arduino sketch that ready analog input A0 to A4 at the requested sampling rate. A Teensy is used instead of a regular Arduino for two reasons. First the Teensy is capable of much higher data throughput, it is able to send five reading at 8000Hz, which is impossible on Arduino. The second reason is the 13bit analog read resolution. Classic Arduino only provides 10 bits.

The software part reads data from the serial port the Teensy is attached to. It interprets the data and stores it in an efficient data-structure. As quickly as possible the data is visualized. The software is written in Java. A recent Java runtime environment is needed to execute it.

Try out the latest version of TeensyDAQ or check out the source code on the github TeensyDAQ source repository.

  • The interface for live visualization.

    The interface for live visualization.

  • The interface allows going back in time and zooming, panning, dragging.

    The interface allows going back in time and zooming, panning, dragging.

  • The ports used by TeensyDAQ marked in green. Mainly A0 to A4.

    The ports used by TeensyDAQ marked in green. Mainly A0 to A4.

  • The hardware: a Teensy and a simple light sensor.

    The hardware: a Teensy and a simple light sensor.

~ TarsosDSP featured in EFY Plus Magazine

EFY Plus July 2015 CoverTarsosDSP, the is a real-time audio processing library written in Java, is featured in EFY Plus Magazine of July 2015. It is a leading electronics magazine with a history going back more than 40 years and about 300 000 subscribers mainly in India. The index mentions this:

TarsosDSP: A Real-Time Audio Analysis and Processing Framework
In last month’s EFY Plus, we discussed Essentia, a C++ library for audio analysis. In this issue we will discuss a Java based real-time audio analysis and processing framework known as TarsosDSP

To read the full article, buy a (digital) copy of the magazine.