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This is Open Source implementation of Audio Processing Technology codec (aptX)
derived from ffmpeg 4.0 project and licensed under LGPLv2.1+. This codec is
mainly used in Bluetooth A2DP profile.

It provides dynamic linked shared library libopenaptx.so and simple command line
utilities openaptxenc and openaptxdec for encoding and decoding operations.
Documentation for shared library is provided in C header file openaptx.h.

There is support for aptX and aptX HD codec variants. Both variants operates on
a raw 24 bit signed stereo audio samples. aptX provides fixed compress ratio 6:1
and aptX HD fixed compress ratio 4:1.

For building and installing into system simply run: make install. For building
without installing run: LD_RUN_PATH='$ORIGIN' make. For producing windows builds
run: make SOFILENAME=openaptx0.dll.

It is suggested to compile library with -O3 optimizations (enabled by default
when env variable CFLAGS is not set) and -mavx2 switch (not enabled by default,
needs CPU with AVX2: Intel Haswell or AMD Excavator) as it provides significant
boost to the performance.

Usage of command line utilities together with sox for resampling or playing:

To convert Wave audio file sample.wav into aptX audio file sample.aptx run:

$ sox sample.wav -t raw -r 44.1k -L -e s -b 24 -c 2 - | openaptxenc > sample.aptx

To convert aptX audio file sample.aptx into Wave audio file sample.wav run:

$ openaptxdec < sample.aptx | sox -t raw -r 44.1k -L -e s -b 24 -c 2 - sample.wav

To convert MP3 audio file sample.mp3 into aptX HD audio file sample.aptxhd run:

$ sox sample.mp3 -t raw -r 44.1k -L -e s -b 24 -c 2 - | openaptxenc --hd > sample.aptxhd

To play aptX HD audio file sample.aptxhd run:

$ openaptxdec --hd < sample.aptxhd | play -t raw -r 44.1k -L -e s -b 24 -c 2 -