gecko-dev/third_party/aom/README.md

# AV1 Codec Library

## Building the library and applications

### Prerequisites

 1. [CMake](https://cmake.org) version 3.5 or higher.
 2. [Git](https://git-scm.com/).
 3. [Perl](https://www.perl.org/).
 4. For x86 targets, [yasm](http://yasm.tortall.net/), which is preferred, or a
    recent version of [nasm](http://www.nasm.us/).
 5. Building the documentation requires [doxygen](http://doxygen.org).
 6. Building the unit tests requires [Python](https://www.python.org/).
 7. Emscripten builds require the portable
   [EMSDK](https://kripken.github.io/emscripten-site/index.html).

### Basic build

CMake replaces the configure step typical of many projects. Running CMake will
produce configuration and build files for the currently selected CMake
generator. For most systems the default generator is Unix Makefiles. The basic
form of a makefile build is the following:

    $ cmake path/to/aom
    $ make

The above will generate a makefile build that produces the AV1 library and
applications for the current host system after the make step completes
successfully. The compiler chosen varies by host platform, but a general rule
applies: On systems where cc and c++ are present in $PATH at the time CMake is
run the generated build will use cc and c++ by default.

### Configuration options

The AV1 codec library has a great many configuration options. These come in two
varieties:

 1. Build system configuration options. These have the form `ENABLE_FEATURE`.
 2. AV1 codec configuration options. These have the form `CONFIG_FEATURE`.

Both types of options are set at the time CMake is run. The following example
enables ccache and disables high bit depth:

~~~
    $ cmake path/to/aom -DENABLE_CCACHE=1 -DCONFIG_HIGHBITDEPTH=0
    $ make
~~~

The available configuration options are too numerous to list here. Build system
configuration options can be found at the top of the CMakeLists.txt file found
in the root of the AV1 repository, and AV1 codec configuration options can
currently be found in the file `build/cmake/aom_config_defaults.cmake`.

### Dylib builds

A dylib (shared object) build of the AV1 codec library can be enabled via the
CMake built in variable `BUILD_SHARED_LIBS`:

~~~
    $ cmake path/to/aom -DBUILD_SHARED_LIBS=1
    $ make
~~~

This is currently only supported on non-Windows targets.

### Debugging

Depending on the generator used there are multiple ways of going about
debugging AV1 components. For single configuration generators like the Unix
Makefiles generator, setting `CMAKE_BUILD_TYPE` to Debug is sufficient:

~~~
    $ cmake path/to/aom -DCMAKE_BUILD_TYPE=Debug
~~~

For Xcode, mainly because configuration controls for Xcode builds are buried two
configuration windows deep and must be set for each subproject within the Xcode
IDE individually, `CMAKE_CONFIGURATION_TYPES` should be set to Debug:

~~~
    $ cmake path/to/aom -G Xcode -DCMAKE_CONFIGURATION_TYPES=Debug
~~~

For Visual Studio the in-IDE configuration controls should be used. Simply set
the IDE project configuration to Debug to allow for stepping through the code.

In addition to the above it can sometimes be useful to debug only C and C++
code. To disable all assembly code and intrinsics set `AOM_TARGET_CPU` to
generic at generation time:

~~~
    $ cmake path/to/aom -DAOM_TARGET_CPU=generic
~~~

### Cross compiling

For the purposes of building the AV1 codec and applications and relative to the
scope of this guide, all builds for architectures differing from the native host
architecture will be considered cross compiles. The AV1 CMake build handles
cross compiling via the use of toolchain files included in the AV1 repository.
The toolchain files available at the time of this writing are:

 - arm64-ios.cmake
 - arm64-linux-gcc.cmake
 - armv7-ios.cmake
 - armv7-linux-gcc.cmake
 - armv7s-ios.cmake
 - mips32-linux-gcc.cmake
 - mips64-linux-gcc.cmake
 - x86-ios-simulator.cmake
 - x86-linux.cmake
 - x86-macos.cmake
 - x86-mingw-gcc.cmake
 - x86\_64-ios-simulator.cmake
 - x86\_64-mingw-gcc.cmake

The following example demonstrates use of the x86-macos.cmake toolchain file on
a x86\_64 MacOS host:

~~~
    $ cmake path/to/aom \
      -DCMAKE_TOOLCHAIN_FILE=path/to/aom/build/cmake/toolchains/x86-macos.cmake
    $ make
~~~

To build for an unlisted target creation of a new toolchain file is the best
solution. The existing toolchain files can be used a starting point for a new
toolchain file since each one exposes the basic requirements for toolchain files
as used in the AV1 codec build.

As a temporary work around an unoptimized AV1 configuration that builds only C
and C++ sources can be produced using the following commands:

~~~
    $ cmake path/to/aom -DAOM_TARGET_CPU=generic
    $ make
~~~

In addition to the above it's important to note that the toolchain files
suffixed with gcc behave differently than the others. These toolchain files
attempt to obey the $CROSS environment variable.

### Sanitizers

Sanitizer integration is built-in to the CMake build system. To enable a
sanitizer, add `-DSANITIZE=<type>` to the CMake command line. For example, to
enable address sanitizer:

~~~
    $ cmake path/to/aom -DSANITIZE=address
    $ make
~~~

Sanitizers available vary by platform, target, and compiler. Consult your
compiler documentation to determine which, if any, are available.

### Microsoft Visual Studio builds

Building the AV1 codec library in Microsoft Visual Studio is supported. The
following example demonstrates generating projects and a solution for the
Microsoft IDE:

~~~
    # This does not require a bash shell; command.exe is fine.
    $ cmake path/to/aom -G "Visual Studio 15 2017"
~~~

### Xcode builds

Building the AV1 codec library in Xcode is supported. The following example
demonstrates generating an Xcode project:

~~~
    $ cmake path/to/aom -G Xcode
~~~

### Emscripten builds

Building the AV1 codec library with Emscripten is supported. Typically this is
used to hook into the AOMAnalyzer GUI application. These instructions focus on
using the inspector with AOMAnalyzer, but all tools can be built with
Emscripten.

It is assumed here that you have already downloaded and installed the EMSDK,
installed and activated at least one toolchain, and setup your environment
appropriately using the emsdk\_env script.

1. Download [AOMAnalyzer](https://people.xiph.org/~mbebenita/analyzer/).

2. Configure the build:

~~~
    $ cmake path/to/aom \
        -DENABLE_CCACHE=1 \
        -DAOM_TARGET_CPU=generic \
        -DENABLE_DOCS=0 \
        -DCONFIG_ACCOUNTING=1 \
        -DCONFIG_INSPECTION=1 \
        -DCONFIG_MULTITHREAD=0 \
        -DCONFIG_RUNTIME_CPU_DETECT=0 \
        -DCONFIG_UNIT_TESTS=0 \
        -DCONFIG_WEBM_IO=0 \
        -DCMAKE_TOOLCHAIN_FILE=path/to/emsdk-portable/.../Emscripten.cmake
~~~

3. Build it: run make if that's your generator of choice:

~~~
    $ make inspect
~~~

4. Run the analyzer:

~~~
    # inspect.js is in the examples sub directory of the directory in which you
    # executed cmake.
    $ path/to/AOMAnalyzer path/to/examples/inspect.js path/to/av1/input/file
~~~


## Testing the AV1 codec

### Testing basics

Currently there are two types of tests in the AV1 codec repository.

#### 1. Unit tests:

The unit tests can be run at build time:

~~~
    # Before running the make command the LIBAOM_TEST_DATA_PATH environment
    # variable should be set to avoid downloading the test files to the
    # cmake build configuration directory.
    $ cmake path/to/aom
    # Note: The AV1 CMake build creates many test targets. Running make
    # with multiple jobs will speed up the test run significantly.
    $ make runtests
~~~

#### 2. Example tests:

The example tests require a bash shell and can be run in the following manner:

~~~
    # See the note above about LIBAOM_TEST_DATA_PATH above.
    $ cmake path/to/aom
    $ make
    # It's best to build the testdata target using many make jobs.
    # Running it like this will verify and download (if necessary)
    # one at a time, which takes a while.
    $ make testdata
    $ path/to/aom/test/examples.sh --bin-path examples
~~~

### IDE hosted tests

By default the generated projects files created by CMake will not include the
runtests and testdata rules when generating for IDEs like Microsoft Visual
Studio and Xcode. This is done to avoid intolerably long build cycles in the
IDEs-- IDE behavior is to build all targets when selecting the build project
options in MSVS and Xcode. To enable the test rules in IDEs the
`ENABLE_IDE_TEST_HOSTING` variable must be enabled at CMake generation time:

~~~
    # This example uses Xcode. To get a list of the generators
    # available, run cmake with the -G argument missing its
    # value.
    $ cmake path/to/aom -DENABLE_IDE_TEST_HOSTING=1 -G Xcode
~~~

### Downloading the test data

The fastest and easiest way to obtain the test data is to use CMake to generate
a build using the Unix Makefiles generator, and then to build only the testdata
rule:

~~~
    $ cmake path/to/aom -G "Unix Makefiles"
    # 28 is used because there are 28 test files as of this writing.
    $ make -j28 testdata
~~~

The above make command will only download and verify the test data.

### Sharded testing

The AV1 codec library unit tests are built upon gtest which supports sharding of
test jobs. Sharded test runs can be achieved in a couple of ways.

#### 1. Running test\_libaom directly:

~~~
   # Set the environment variable GTEST_TOTAL_SHARDS to 9 to run 10 test shards
   # (GTEST shard indexing is 0 based).
   $ export GTEST_TOTAL_SHARDS=9
   $ seq 0 $(( $GTEST_TOTAL_SHARDS - 1 )) \
       | xargs -n 1 -P 0 -I{} env GTEST_SHARD_INDEX={} ./test_libaom
~~~

To create a test shard for each CPU core available on the current system set
`GTEST_TOTAL_SHARDS` to the number of CPU cores on your system minus one.

#### 2. Running the tests via the CMake build:

~~~
    # For IDE based builds, ENABLE_IDE_TEST_HOSTING must be enabled. See
    # the IDE hosted tests section above for more information. If the IDE
    # supports building targets concurrently tests will be sharded by default.

    # For make and ninja builds the -j parameter controls the number of shards
    # at test run time. This example will run the tests using 10 shards via
    # make.
    $ make -j10 runtests
~~~

The maximum number of test targets that can run concurrently is determined by
the number of CPUs on the system where the build is configured as detected by
CMake. A system with 24 cores can run 24 test shards using a value of 24 with
the `-j` parameter. When CMake is unable to detect the number of cores 10 shards
is the default maximum value.

## Coding style

The coding style used by this project is enforced with clang-format using the
configuration contained in the .clang-format file in the root of the repository.

Before pushing changes for review you can format your code with:

~~~
    # Apply clang-format to modified .c, .h and .cc files
    $ clang-format -i --style=file \
      $(git diff --name-only --diff-filter=ACMR '*.[hc]' '*.cc')
~~~

Check the .clang-format file for the version used to generate it if there is any
difference between your local formatting and the review system.

See also: http://clang.llvm.org/docs/ClangFormat.html

## Support

This library is an open source project supported by its community. Please
please email aomediacodec@jointdevelopment.kavi.com for help.

## Bug reports

Bug reports can be filed in the Alliance for Open Media
[issue tracker](https://bugs.chromium.org/p/aomedia/issues/list).