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Reverse-engineered apt-X audio codec

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[open]aptx - reverse-engineered apt-X

This project is for research purposes only. Without a proper license private and commercial usage might be a case of a patent infringement. If you are looking for a library, which can be installed and used legally (commercial, private and educational usage), go to the Qualcomm® aptX™ homepage and contact Qualcomm customer service.

The source code itself is licensed under the terms of the MIT license. However, compression algorithms are patented and licensed under the terms of a proprietary license. Hence, compilation and redistribution in a binary format is forbidden!

Compilation

mkdir build && cd build
cmake -DENABLE_DOC=ON -DWITH_FFMPEG=ON -DWITH_SNDFILE=ON ..
make && make install

Configure options

  • ENABLE_DOC - build and install manual files (requires Doxygen)
  • ENABLE_APTX_DECODER_API - build with apt-X / apt-X HD decoder API (default: ON)
  • ENABLE_APTX_ENCODER_API - build with apt-X / apt-X HD encoder API (default: ON)
  • ENABLE_APTX422 - build reverse engineered apt-X library based on bt-aptX-x86-4.2.2.so
  • ENABLE_APTXHD100 - build reverse engineered apt-X HD library based on aptXHD-1.0.0-ARMv7A
  • WITH_FFMPEG - use FFmpeg as a back-end (otherwise, stub library will be built)
  • WITH_SNDFILE - read file formats supported by libsndfile (used by openaptx utils)

In the apt-X stub library (build without FFmpeg back-end), all symbols are exported as weak. As a consequence, it should be possible to overwrite them during runtime with other library which exports strong symbols. However, it might be required to define LD_DYNAMIC_WEAK environment variable - for more information consult ld.so manual.

When reverse-engineered libraries were enabled, they will be automatically linked with the apt-X stub library (build without FFmpeg back-end). See previous paragraph for the meaning of this.

Benchmark

Below is the result of a small benchmark test performed with various apt-X encoding libraries. Test was done with the usage of aptxenc and aptxhdenc tools from this repository. Elapsed user time was calculated with the usage of a standard UNIX time command line tool. All libraries (except original Qualcomm libraries) were compiled with Clang version 8.0.7 with the O2 or O3 optimization level.

Setup

  • CPU: ARM Cortex-A53
  • Input file: WAV audio, Microsoft PCM, 16 bit, stereo 48000 Hz
  • Input duration: 15 minutes 45 seconds

Results

Library apt-X Mbit/s apt-X HD Mbit/s
libaptX-1.0.16-rel-Android21 1m00.370s 1.23673
libaptXHD-1.0.1-rel-Android21 1m07.030s 1.11109
openaptx-stub 0m04.480s 0.0 0m04.820s 0.0
openaptx-ffmpeg (libavcodec-58.54.100) 1m58.100s 0.60835 2m03.270s 0.58354
aptx422 1m19.840s 0.91721
aptxHD100 1m21.950s 0.89616
libopenaptx-0.2.0 1m22.090s 0.89062 1m25.730s 0.85429

Resources

  1. AptX audio codec family
  2. Method and apparatus for electrical signal coding
  3. Two-channel QMF bank