summaryrefslogtreecommitdiffstats
path: root/third_party/aom/README.md
diff options
context:
space:
mode:
authorDaniel Baumann <daniel.baumann@progress-linux.org>2024-04-19 00:47:55 +0000
committerDaniel Baumann <daniel.baumann@progress-linux.org>2024-04-19 00:47:55 +0000
commit26a029d407be480d791972afb5975cf62c9360a6 (patch)
treef435a8308119effd964b339f76abb83a57c29483 /third_party/aom/README.md
parentInitial commit. (diff)
downloadfirefox-26a029d407be480d791972afb5975cf62c9360a6.tar.xz
firefox-26a029d407be480d791972afb5975cf62c9360a6.zip
Adding upstream version 124.0.1.upstream/124.0.1
Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
Diffstat (limited to '')
-rw-r--r--third_party/aom/README.md677
1 files changed, 677 insertions, 0 deletions
diff --git a/third_party/aom/README.md b/third_party/aom/README.md
new file mode 100644
index 0000000000..4e2eb2756c
--- /dev/null
+++ b/third_party/aom/README.md
@@ -0,0 +1,677 @@
+README.md {#LREADME}
+=========
+# AV1 Codec Library
+
+## Contents
+1. [Building the lib and applications](#building-the-library-and-applications)
+ - [Prerequisites](#prerequisites)
+ - [Get the code](#get-the-code)
+ - [Basics](#basic-build)
+ - [Configuration options](#configuration-options)
+ - [Dylib builds](#dylib-builds)
+ - [Debugging](#debugging)
+ - [Cross compiling](#cross-compiling)
+ - [Sanitizer support](#sanitizers)
+ - [MSVC builds](#microsoft-visual-studio-builds)
+ - [Xcode builds](#xcode-builds)
+ - [Emscripten builds](#emscripten-builds)
+ - [Extra Build Flags](#extra-build-flags)
+ - [Build with VMAF support](#build-with-vmaf)
+2. [Testing the library](#testing-the-av1-codec)
+ - [Basics](#testing-basics)
+ - [Unit tests](#unit-tests)
+ - [Example tests](#example-tests)
+ - [Encoder tests](#encoder-tests)
+ - [IDE hosted tests](#ide-hosted-tests)
+ - [Downloading test data](#downloading-the-test-data)
+ - [Adding a new test data file](#adding-a-new-test-data-file)
+ - [Additional test data](#additional-test-data)
+ - [Sharded testing](#sharded-testing)
+ - [Running tests directly](#running-test_libaom-directly)
+ - [Running tests via CMake](#running-the-tests-via-the-cmake-build)
+3. [Coding style](#coding-style)
+4. [Submitting patches](#submitting-patches)
+ - [Login cookie](#login-cookie)
+ - [Contributor agreement](#contributor-agreement)
+ - [Testing your code](#testing-your-code)
+ - [Commit message hook](#commit-message-hook)
+ - [Upload your change](#upload-your-change)
+ - [Incorporating Reviewer Comments](#incorporating-reviewer-comments)
+ - [Submitting your change](#submitting-your-change)
+ - [Viewing change status](#viewing-the-status-of-uploaded-changes)
+5. [Support](#support)
+6. [Bug reports](#bug-reports)
+
+## Building the library and applications {#building-the-library-and-applications}
+
+### Prerequisites {#prerequisites}
+
+ 1. [CMake](https://cmake.org). See CMakeLists.txt for the minimum version
+ required.
+ 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/). If you download yasm with
+ the intention to work with Visual Studio, please download win32.exe or
+ win64.exe and rename it into yasm.exe. DO NOT download or use vsyasm.exe.
+ 5. Building the documentation requires
+ [doxygen version 1.8.10 or newer](http://doxygen.org).
+ 6. Emscripten builds require the portable
+ [EMSDK](https://kripken.github.io/emscripten-site/index.html).
+
+### Get the code {#get-the-code}
+
+The AV1 library source code is stored in the Alliance for Open Media Git
+repository:
+
+~~~
+ $ git clone https://aomedia.googlesource.com/aom
+ # By default, the above command stores the source in the aom directory:
+ $ cd aom
+~~~
+
+### Basic build {#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 {#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 the AV1 encoder:
+
+~~~
+ $ cmake path/to/aom -DENABLE_CCACHE=1 -DCONFIG_AV1_ENCODER=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 {#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 {#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 {#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-clang.cmake
+ - arm64-linux-gcc.cmake
+ - arm64-mingw-gcc.cmake
+ - armv7-ios.cmake
+ - armv7-linux-gcc.cmake
+ - armv7-mingw-gcc.cmake
+ - armv7s-ios.cmake
+ - ppc-linux-gcc.cmake
+ - riscv-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 {#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 {#microsoft-visual-studio-builds}
+
+Building the AV1 codec library in Microsoft Visual Studio is supported. Visual
+Studio 2019 (16.0) or later is required. The following example demonstrates
+generating projects and a solution for the Microsoft IDE:
+
+~~~
+ # This does not require a bash shell; Command Prompt (cmd.exe) is fine.
+ # This assumes the build host is a Windows x64 computer.
+
+ # To create a Visual Studio 2022 solution for the x64 target:
+ $ cmake path/to/aom -G "Visual Studio 17 2022"
+
+ # To create a Visual Studio 2022 solution for the 32-bit x86 target:
+ $ cmake path/to/aom -G "Visual Studio 17 2022" -A Win32
+
+ # To create a Visual Studio 2019 solution for the x64 target:
+ $ cmake path/to/aom -G "Visual Studio 16 2019"
+
+ # To create a Visual Studio 2019 solution for the 32-bit x86 target:
+ $ cmake path/to/aom -G "Visual Studio 16 2019" -A Win32
+
+ # To build the solution:
+ $ cmake --build .
+~~~
+
+NOTE: The build system targets Windows 7 or later by compiling files with
+`-D_WIN32_WINNT=0x0601`.
+
+### Xcode builds {#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 {#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. Build [AOM Analyzer](https://github.com/xiph/aomanalyzer).
+
+2. Configure the build:
+
+~~~
+ $ cmake path/to/aom \
+ -DENABLE_CCACHE=1 \
+ -DAOM_TARGET_CPU=generic \
+ -DENABLE_DOCS=0 \
+ -DENABLE_TESTS=0 \
+ -DCONFIG_ACCOUNTING=1 \
+ -DCONFIG_INSPECTION=1 \
+ -DCONFIG_MULTITHREAD=0 \
+ -DCONFIG_RUNTIME_CPU_DETECT=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
+~~~
+
+### Extra build flags {#extra-build-flags}
+
+Three variables allow for passing of additional flags to the build system.
+
+- AOM\_EXTRA\_C\_FLAGS
+- AOM\_EXTRA\_CXX\_FLAGS
+- AOM\_EXTRA\_EXE\_LINKER\_FLAGS
+
+The build system attempts to ensure the flags passed through the above variables
+are passed to tools last in order to allow for override of default behavior.
+These flags can be used, for example, to enable asserts in a release build:
+
+~~~
+ $ cmake path/to/aom \
+ -DCMAKE_BUILD_TYPE=Release \
+ -DAOM_EXTRA_C_FLAGS=-UNDEBUG \
+ -DAOM_EXTRA_CXX_FLAGS=-UNDEBUG
+~~~
+
+### Build with VMAF support {#build-with-vmaf}
+
+After installing
+[libvmaf.a](https://github.com/Netflix/vmaf/tree/master/libvmaf),
+you can use it with the encoder:
+
+~~~
+ $ cmake path/to/aom -DCONFIG_TUNE_VMAF=1
+~~~
+
+Please note that the default VMAF model
+("/usr/local/share/model/vmaf_v0.6.1.json")
+will be used unless you set the following flag when running the encoder:
+
+~~~
+ # --vmaf-model-path=path/to/model
+~~~
+
+## Testing the AV1 codec {#testing-the-av1-codec}
+
+### Testing basics {#testing-basics}
+
+There are several methods of testing the AV1 codec. All of these methods require
+the presence of the AV1 source code and a working build of the AV1 library and
+applications.
+
+#### 1. Unit tests: {#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: {#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
+~~~
+
+#### 3. Encoder tests: {#encoder-tests}
+
+When making a change to the encoder run encoder tests to confirm that your
+change has a positive or negligible impact on encode quality. When running these
+tests the build configuration should be changed to enable internal encoder
+statistics:
+
+~~~
+ $ cmake path/to/aom -DCONFIG_INTERNAL_STATS=1
+ $ make
+~~~
+
+The repository contains scripts intended to make running these tests as simple
+as possible. The following example demonstrates creating a set of baseline clips
+for comparison to results produced after making your change to libaom:
+
+~~~
+ # This will encode all Y4M files in the current directory using the
+ # settings specified to create the encoder baseline statistical data:
+ $ cd path/to/test/inputs
+ # This command line assumes that run_encodes.sh, its helper script
+ # best_encode.sh, and the aomenc you intend to test are all within a
+ # directory in your PATH.
+ $ run_encodes.sh 200 500 50 baseline
+~~~
+
+After making your change and creating the baseline clips, you'll need to run
+encodes that include your change(s) to confirm that things are working as
+intended:
+
+~~~
+ # This will encode all Y4M files in the current directory using the
+ # settings specified to create the statistical data for your change:
+ $ cd path/to/test/inputs
+ # This command line assumes that run_encodes.sh, its helper script
+ # best_encode.sh, and the aomenc you intend to test are all within a
+ # directory in your PATH.
+ $ run_encodes.sh 200 500 50 mytweak
+~~~
+
+After creating both data sets you can use `test/visual_metrics.py` to generate a
+report that can be viewed in a web browser:
+
+~~~
+ $ visual_metrics.py metrics_template.html "*stt" baseline mytweak \
+ > mytweak.html
+~~~
+
+You can view the report by opening mytweak.html in a web browser.
+
+
+### IDE hosted tests {#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 {#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. By default the test files will be downloaded to the current directory. The
+`LIBAOM_TEST_DATA_PATH` environment variable can be used to set a
+custom one.
+
+~~~
+ $ 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.
+
+### Adding a new test data file {#adding-a-new-test-data-file}
+
+First, add the new test data file to the `aom-test-data` bucket of the
+`aomedia-testing` project on Google Cloud Platform. You may need to ask someone
+with the necessary access permissions to do this for you.
+
+NOTE: When a new test data file is added to the `aom-test-data` bucket, its
+"Public access" is initially "Not public". We need to change its
+"Public access" to "Public" by using the following
+[`gsutil`](https://cloud.google.com/storage/docs/gsutil_install) command:
+~~~
+ $ gsutil acl ch -g all:R gs://aom-test-data/test-data-file-name
+~~~
+This command grants the `AllUsers` group READ access to the file named
+"test-data-file-name" in the `aom-test-data` bucket.
+
+Once the new test data file has been added to `aom-test-data`, create a CL to
+add the name of the new test data file to `test/test_data_util.cmake` and add
+the SHA1 checksum of the new test data file to `test/test-data.sha1`. (The SHA1
+checksum of a file can be calculated by running the `sha1sum` command on the
+file.)
+
+### Additional test data {#additional-test-data}
+
+The test data mentioned above is strictly intended for unit testing.
+
+Additional input data for testing the encoder can be obtained from:
+https://media.xiph.org/video/derf/
+
+### Sharded testing {#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: {#running-test_libaom-directly}
+
+~~~
+ # Set the environment variable GTEST_TOTAL_SHARDS to control the number of
+ # shards.
+ $ export GTEST_TOTAL_SHARDS=10
+ # (GTEST shard indexing is 0 based).
+ $ 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: {#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 {#coding-style}
+
+We are using the Google C Coding Style defined by the
+[Google C++ Style Guide](https://google.github.io/styleguide/cppguide.html).
+
+The coding style used by this project is enforced with clang-format using the
+configuration contained in the
+[.clang-format](https://chromium.googlesource.com/webm/aom/+/main/.clang-format)
+file in the root of the repository.
+
+You can download clang-format using your system's package manager, or directly
+from [llvm.org](http://llvm.org/releases/download.html). You can also view the
+[documentation](https://clang.llvm.org/docs/ClangFormat.html) on llvm.org.
+Output from clang-format varies by clang-format version, for best results your
+version should match the one used on Jenkins. You can find the clang-format
+version by reading the comment in the `.clang-format` file linked above.
+
+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.
+
+Some Git installations have clang-format integration. Here are some examples:
+
+~~~
+ # Apply clang-format to all staged changes:
+ $ git clang-format
+
+ # Clang format all staged and unstaged changes:
+ $ git clang-format -f
+
+ # Clang format all staged and unstaged changes interactively:
+ $ git clang-format -f -p
+~~~
+
+## Submitting patches {#submitting-patches}
+
+We manage the submission of patches using the
+[Gerrit](https://www.gerritcodereview.com/) code review tool. This tool
+implements a workflow on top of the Git version control system to ensure that
+all changes get peer reviewed and tested prior to their distribution.
+
+### Login cookie {#login-cookie}
+
+Browse to [AOMedia Git index](https://aomedia.googlesource.com/) and login with
+your account (Gmail credentials, for example). Next, follow the
+`Generate Password` Password link at the top of the page. You’ll be given
+instructions for creating a cookie to use with our Git repos.
+
+You must also have a Gerrit account associated with your Google account. To do
+this visit the [Gerrit review server](https://aomedia-review.googlesource.com)
+and click "Sign in" (top right).
+
+### Contributor agreement {#contributor-agreement}
+
+You will be required to execute a
+[contributor agreement](http://aomedia.org/license) to ensure that the AOMedia
+Project has the right to distribute your changes.
+
+Note: If you are pushing changes on behalf of an Alliance for Open Media member
+organization this step is not necessary.
+
+### Testing your code {#testing-your-code}
+
+The testing basics are covered in the [testing section](#testing-the-av1-codec)
+above.
+
+In addition to the local tests, many more (e.g. asan, tsan, valgrind) will run
+through Jenkins instances upon upload to gerrit.
+
+### Commit message hook {#commit-message-hook}
+
+Gerrit requires that each submission include a unique Change-Id. You can assign
+one manually using git commit --amend, but it’s easier to automate it with the
+commit-msg hook provided by Gerrit.
+
+Copy commit-msg to the `.git/hooks` directory of your local repo. Here's an
+example:
+
+~~~
+ $ curl -Lo aom/.git/hooks/commit-msg https://chromium-review.googlesource.com/tools/hooks/commit-msg
+
+ # Next, ensure that the downloaded commit-msg script is executable:
+ $ chmod u+x aom/.git/hooks/commit-msg
+~~~
+
+See the Gerrit
+[documentation](https://gerrit-review.googlesource.com/Documentation/user-changeid.html)
+for more information.
+
+### Upload your change {#upload-your-change}
+
+The command line to upload your patch looks like this:
+
+~~~
+ $ git push https://aomedia-review.googlesource.com/aom HEAD:refs/for/main
+~~~
+
+### Incorporating reviewer comments {#incorporating-reviewer-comments}
+
+If you previously uploaded a change to Gerrit and the Approver has asked for
+changes, follow these steps:
+
+1. Edit the files to make the changes the reviewer has requested.
+2. Recommit your edits using the --amend flag, for example:
+
+~~~
+ $ git commit -a --amend
+~~~
+
+3. Use the same git push command as above to upload to Gerrit again for another
+ review cycle.
+
+In general, you should not rebase your changes when doing updates in response to
+review. Doing so can make it harder to follow the evolution of your change in
+the diff view.
+
+### Submitting your change {#submitting-your-change}
+
+Once your change has been Approved and Verified, you can “submit” it through the
+Gerrit UI. This will usually automatically rebase your change onto the branch
+specified.
+
+Sometimes this can’t be done automatically. If you run into this problem, you
+must rebase your changes manually:
+
+~~~
+ $ git fetch
+ $ git rebase origin/branchname
+~~~
+
+If there are any conflicts, resolve them as you normally would with Git. When
+you’re done, reupload your change.
+
+### Viewing the status of uploaded changes {#viewing-the-status-of-uploaded-changes}
+
+To check the status of a change that you uploaded, open
+[Gerrit](https://aomedia-review.googlesource.com/), sign in, and click My >
+Changes.
+
+## Support {#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}
+
+Bug reports can be filed in the Alliance for Open Media
+[issue tracker](https://bugs.chromium.org/p/aomedia/issues/list).