[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

Prerequisites

• CMake 3.22 or newer
• Doxygen (optional)
• FFmpeg 5.1.0 or newer (optional)
• libfreeaptx 0.1.0 or newer (optional)
• libsndfile 1.0.19 or newer (optional)

# Install required packages on Debian-based systems
sudo apt-get install cmake doxygen ffmpeg libfreeaptx-dev libsndfile1-dev

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_FREEAPTX - use libfreeaptx as a back-end (FFmpeg back-end must be disabled)
• 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 9.0.0 with the 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	1m01s	23.8	—	—
libaptXHD-1.0.1-rel-Android21	—	—	1m04s	22.7
openaptx-stub	0m11s	0.0	0m11s	0.0
openaptx-ffmpeg (libavcodec-59.37.100)	2m12s	11.0	2m18s	10.5
aptx422	1m14s	19.6	—	—
aptxHD100	—	—	1m16s	19.1
libopenaptx-0.2.0	1m17s	18.8	1m19s	18.4

Resources

1. AptX audio codec family
2. AptX encoder source code
3. AptX HD encoder source code
4. Method and apparatus for electrical signal coding
5. Two-channel QMF bank