[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