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WebRTC:NativeCode

lastmod 2020-02-23created 2019-02-1249 edits

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How to install

First install depot_tools and set the PATH environment variable. Do not get the code with the git clone command; proceed as follows instead. 

$ mkdir webrtc-checkout
$ cd webrtc-checkout
$ fetch --nohooks webrtc

Move into the generated src directory. 

$ cd src

Switch to the desired branch. 

$ git branch --remote
$ git checkout branch-heads/70

Sync: 

$ gclient sync

On macOS, running gn may fail at the command that looks up the SDK path, such as python webrtc-checkout/src/build/mac/find_sdk.py --print_sdk_path 10.12. In that case, run the following command first. 

## Install Xcode, launch it, accept the license agreement, and run
$ sudo xcode-select -s /Applications/Xcode.app

Generate the ninja project. 

## Generating Ninja project files
$ gn gen out/Default

## or Release mode:
$ gn gen out/Default --args='is_debug=false'

## clean:
$ gn clean out/Default

Compiling: 

$ ninja -C out/Default

Diagram

Block Diagram

WebRTCNativeAPIsDocument_-_Block_Diagram.png

Set up a call

WebRTCNativeAPIsDocument_-_Set_up_a_call.png

Receive a Call

WebRTCNativeAPIsDocument_-_Receive_a_Call.png

Close Down a Call

WebRTCNativeAPIsDocument_-_Close_Down_a_Call.png

gn arguments

Describes the variables that can be applied in gn, as in gn gen out/Default --args='is_debug=false'.

The full list can be viewed with gn args out/Default --list. Also available in WebRTC:NativeCode:GnArgumentList.

enable_nacl=false
Disable Native Client.
Most developers don't normally need to test Native Client capabilities and can speed up the build by disabling it.
blink_symbol_level=0
Remove WebCore symbols
WebCore has lots of templates that account for a large portion of the debugging symbols. If you're not debugging WebCore, you can skip these symbols to make the build smaller and faster.
is_debug=false
Apply for release builds.
rtc_use_h264=true
Enable this to build OpenH264 encoder/FFmpeg decoder. This is supported on all platforms except Android and iOS. Because FFmpeg can be built with/without H.264 support, |ffmpeg_branding| has to separately be set to a value that includes H.264, for example "Chrome". If FFmpeg is built without H.264, compilation succeeds but |H264DecoderImpl| fails to initialize.
CHECK THE OPENH264, FFMPEG AND H.264 LICENSES/PATENTS BEFORE BUILDING.
ffmpeg_branding
Controls whether we build the Chromium or Google Chrome version of FFmpeg. The Google Chrome version contains additional codecs. Typical values are Chromium, Chrome, and ChromeOS.
symbol_level
How many symbols to include in the build. This affects the performance of the build since the symbols are large and dealing with them is slow.
  • 2: means regular build with symbols.
  • 1: means minimal symbols, usually enough for backtraces only. Symbols with internal linkage (static functions or those in anonymous namespaces) may not appear when using this level.
  • 0: means no symbols.
  • -1: means auto-set according to debug/release and platform.
use_rtti
Build with C++ RTTI enabled. Chromium builds without RTTI by default, but some sanitizers are known to require it, like CFI diagnostics and UBsan variants.

Target visibility and the native API

The WebRTC-specific GN templates declare build targets whose default visibility allows all other targets in the WebRTC tree (and no targets outside the tree) to depend on them.

Prefer to restrict the visibility if possible:

  • If a target is used by only one or a tiny number of other targets, prefer to list them explicitly: visibility = [ ":foo", ":bar" ]
  • If a target is used only by targets in the same BUILD.gn file: visibility = [ ":*" ].

Setting visibility = [ "*" ] means that targets outside the WebRTC tree can depend on this target; use this only for build targets whose headers are part of the native API.

H264 encode/decode support

Apply the gn arguments as follows. 

$ gn gen out/release --args='ffmpeg_branding="Chrome" rtc_use_h264=true is_debug=false'

Sample program

A sample program for testing that WebRTC works. Tested on branch-heads/72.

cmake build script. 

# libsourcey WebRTC Video Server

cmake_minimum_required (VERSION 2.8)

set (PROJECT_NAME sourecy)
project (${PROJECT_NAME})

set (CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++11")

set (SOURCE_FILES main.cpp)
add_executable (${PROJECT_NAME} ${SOURCE_FILES})

set (WEBRTC_PREFIX /usr/local/c2core/webrtc)

set (WEBRTC_INCLUDE_DIRS
        ${WEBRTC_PREFIX}/include
        ${WEBRTC_PREFIX}/include/third_party/abseil-cpp)
set (WEBRTC_INCLUDE_LIBS
        -Wl,-force_load,${WEBRTC_PREFIX}/lib/libwebrtc.a
        "-framework Foundation"
        "-framework AVFoundation"
        "-framework CoreAudio"
        "-framework AudioToolbox"
        "-framework CoreFoundation"
        "-framework CoreGraphics"
        "-framework CoreMedia"
        "-framework CoreVideo"
        "-framework IOSurface"
        "-framework Cocoa")

#"-framework IOKit"
#"-framework Security"
#"-framework SystemConfiguration"
#"-framework ApplicationServices"
#"-framework OpenGL"
#"-framework VideoToolbox"

target_compile_definitions (${PROJECT_NAME} PRIVATE WEBRTC_MAC WEBRTC_POSIX)
target_include_directories (${PROJECT_NAME} PRIVATE ${WEBRTC_INCLUDE_DIRS})
target_link_libraries (${PROJECT_NAME} PRIVATE ${WEBRTC_INCLUDE_LIBS})

C/C++ main source: 

#include <iostream>
#include <rtc_base/ssladapter.h>

int main()
{
    rtc::InitializeSSL();

    using namespace std;
    cout << "Hello, World!" << endl;

    rtc::CleanupSSL();
    return 0;
}

MediaStream

Troubleshooting

Direct access to weak symbols 

ld: warning: direct access in function 'webrtc::AudioEncoderIlbc::QueryAudioEncoder(webrtc::AudioEncoderIlbcConfig const&)' from file '/usr/local/c2core/webrtc/lib/libwebrtc.a(audio_encoder_ilbc.o)' to global weak symbol 'void rtc::webrtc_checks_impl::LogStreamer<>::Call<>(char const*, int, char const*)::t' from file 'CMakeFiles/c2media.dir/libc2media/temp/webrtc-streamer/rtspaudiocapturer.cpp.o' means the weak symbol cannot be overridden at runtime. This was likely caused by different translation units being compiled with different visibility settings.

rtc::Thread::Current() is nullptr

If rtc::Thread::Current() returns nullptr on a separate thread other than the main thread, initialize it as follows. 

webrtc_thread = rtc::Thread::CreateWithSocketServer();
assert(static_cast<bool>(webrtc_thread));

auto * thread_manger = rtc::ThreadManager::Instance();
assert(thread_manger != nullptr);
thread_manger->SetCurrentThread(webrtc_thread.get());

manager = std::make_unique<WrxPcManager>();
manager->setCallback(this);
if (!manager->existsPeerConnection()) {
    throw ErrException(E_INIT);
}

auto * thread = rtc::Thread::Current();
assert(webrtc_thread.get() == thread);

See also

Favorite site

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