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119 lines
3.0 KiB
Markdown
119 lines
3.0 KiB
Markdown
# Low Complexity Communication Codec (LC3)
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The LC3 is an efficient low latency audio codec.
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[_Low Complexity Communication Codec_](https://www.bluetooth.org/DocMan/handlers/DownloadDoc.ashx?doc_id=502107&vId=542963)
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## Overview
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The directory layout is as follows :
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- include: Library interface
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- src: Source files
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- tools: Standalone encoder/decoder tools
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- test: Python implentation, used as reference for unit testing
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- build: Building outputs
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- bin: Compilation output
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## How to build
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The default toolchain used is GCC. Invoke `make` to build the library.
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```sh
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$ make -j
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```
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Compiled library `liblc3.a` will be found in `bin` directory.
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#### Cross compilation
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The cc, as, ld and ar can be selected with respective Makefile variables `CC`,
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`AS`, `LD` and `AR`. The `AS` and `LD` selections are optionnal, and fallback
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to `CC` selection when not defined.
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The `LIBC` must be set to `bionic` for android cross-compilation. This switch
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prevent link with `pthread` and `rt` libraries, that is included in the
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bionic libc.
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Following example build for android, using NDK toolset.
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```sh
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$ make -j CC=path_to_android_ndk_prebuilt/toolchain-prefix-clang LIBC=bionic
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```
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Compiled library will be found in `bin` directory.
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## Tools
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Tools can be all compiled, while involking `make` as follows :
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```sh
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$ make tools
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```
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The standalone encoder `elc3` take a `wave` file as input and encode it
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according given parameter. The LC3 binary file format used is the non
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standard format described by the reference encoder / decoder tools.
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The standalone decoder `dlc3` do the inverse operation.
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Refer to `elc3 -h` or `dlc3 -h` for options.
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Note that `elc3` output bitstream to standard output when output file is
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omitted. On the other side `dlc3` read from standard input when input output
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file are omitted.
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In such way you can easly test encoding / decoding loop with :
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```sh
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$ ./elc3 <in.wav> -b <bitrate> | ./dlc3 > <out.wav>
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```
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Adding Linux `aplay` tools, you will be able to instant hear the result :
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```sh
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$ ./elc3 <in.wav> -b <bitrate> | ./dlc3 | aplay
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```
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## Test
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A python implementation of the encoder is provided in `test` diretory.
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The C implementation is unitary validated against this implementation and
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intermediate values given in Appendix C of the specification.
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#### Prerequisite
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```sh
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# apt install python3 python3-dev python3-pip
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$ pip3 install scipy numpy
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```
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#### Running test suite
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```sh
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$ make test
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```
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## Conformance
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The proposed encoder and decoder implementation have been fully tested and
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validated.
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For more detail on conformance, refer to [_Bluetooth Conformance
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Documents and scripts_](https://www.bluetooth.com/specifications/specs/low-complexity-communication-codec-1-0/)
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## Listening Test
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The codec was [_here_](https://hydrogenaud.io/index.php/topic,122575.0.html)
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subjectively evaluated in a blind listening test.
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## Meson build system
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Meson build system is also available to build and install lc3 codec in Linux
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environment.
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```sh
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$ meson build
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$ cd build
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$ ninja
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$ sudo ninja install
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```
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