exhale/README.md

exhale
======

exhale, which is an acronym for "Ecodis eXtended High-efficiency And
Low-complexity Encoder", is a lightweight library and application to
encode uncompressed WAVE-format audio files into MPEG-4-format files
complying with the ISO/IEC 23003-3 (MPEG-D) Unified Speech and Audio
Coding (USAC, also known as Extended High-Efficiency AAC) standard.

In addition, exhale writes program peak-level and loudness data into
the generated MPEG-4 files according to the ISO/IEC 23003-4, Dynamic
Range Control (DRC) specification for use by decoders providing DRC.

exhale currently makes use of all frequency-domain (FD) coding tools
in the scalefactor based MDCT processing path. Its objective is high
quality mono, stereo, and multichannel coding at medium and high bit
rates, so the lower-rate USAC coding tools (ACELP, TCX, Enhanced SBR
and MPEG Surround with Unified Stereo coding) won't be integrated.

____________________________________________________________________


Copyright
---------

(c) 2020 Christian R. Helmrich, project ecodis. All rights reserved.


License
-------

exhale is being made available under an open-source license which is
based on the 3-clause BSD license but modified to address particular
aspects dictated by the nature and the output of this application.

The license text and release notes for the current version 1.1.1 can
be found in the `include` subdirectory of the exhale distribution.


Compilation
-----------

This section describes how to compile the exhale source code into an
executable application under Linux and Microsoft Windows. The binary
application files will show up in a newly created `bin` subdirectory
of the exhale distribution directory and/or a subdirectory thereof.

Note that, for advanced use cases, cmake files are provided as well.
See https://gitlab.com/ecodis/exhale/-/merge_requests/2 for details.

### Linux and MacOS (GNU Compiler Collection, gcc):

In a terminal, change to the exhale distribution directory and enter

`
make release
`

to build a release-mode executable with the default (usually 64-bit)
configuration. A 32-bit debug-mode executable can be built by typing

`
make BUILD32=1 debug
`

### Microsoft Windows (Visual Studio 2012 and later):

Doubleclick the exhale_vs2012.sln file to open the project in Visual
Studio. Once it's loaded, rightclick on `exhaleApp` in the "Solution
Explorer" window on the right-hand side, then select `Set as StartUp
Project`. Now simply press `F7` to build the solution in debug mode.

To change the debugging command, rightclick again on `exhaleApp` and
select `Properties`. In the newly opened window click on `Debugging`
under "Configuration Properties" on the left-hand side. Then you can
edit the "Command Arguments" entry on the right-hand side as needed.

For fastest encoding speed, please select `Release` and `x64` before
building the solution. This will create a release-mode 64-bit binary.
If you would like to build a dynamically linked library (DLL) of the
exhale source instead of an application binary, select `Release DLL`
instead of `Release`, rightclick on `exhaleLib`, and select `Build`.


Usage
-----

This section describes how to run the exhale application either from
the command-line or using a third-party software providing WAVE data
to exhale's standard input pipe (stdin), such as foobar2000.

### Standalone (command-line):

In a terminal, change to exhale's `bin` subdirectory and then enter

`./exhale` (on Linux and MacOS) or `exhale.exe` (on Windows)

to print out usage information. As an example, the following command

`exhale.exe 5 C:\Music\Input.wav C:\Music\Output.m4a`

converts file Input.wav to file Output.m4a at roughly 128 kbit/s (if
the input signal is two-channel stereo) and in xHE-AAC audio format.
Note that, when calling the exhale application with a path (such as,
e.g., `bin/exhale` or `bin\exhale.exe`), but specifying the input or
output file without a file path (e.g., `Input.wav`), those files are
assumed to be located in the application path (here, `bin`). Use the
"dot prefix" to indicate files in the *current* directory instead of
the application directory (here, `./Input.wav` or `.\Input.wav`).


### Third-party stdin (foobar2000):

After downloading from www.foobar2000.org and starting the software,
load the desired input audio files into the playlist. Mark all files
to be converted, rightclick on one of them, and select `Convert` ->
`...`. In the newly opened window click on `Output format` and, once
the window content changed, on `Add New`. Then select `Custom` under
"Encoder" and enter the following information:

- *Encoder file:* exhale.exe (including path to the executable)
- *Extension:* m4a
- *Parameters:* # %d (where # is the bit-rate mode, i.e., 0...9 when
                      SBR is disabled, or a...g when SBR is enabled)
- *Format is:* lossy
- *Highest BPS mode supported:* 24 (or 32, doesn't matter much)
- *Encoder name:* xHE-AAC (exhale)
- *Bitrate (kbps):* (depends on bit-rate mode, see Usage above)
- *Settings:* CVBR mode # (where # equals that in *Parameters*)

Then click on `OK` and on `Back` and, in the first "Converter Setup"
window, on `Other` and ensure the "Transfer..." box for the class of
input metadata that you wish to copy to the output files is checked.
Now set the destination settings as desired and click on `Convert`.


Development
-----------

If you are interested in contributing to exhale, please email one of
the developers. Merge requests with fixes and/or speedups are highly
appreciated.