H.264: Default flags and pulling in openh264 and ffmpeg.

Defining use_third_party_h264 directly, and indirectly defining use_openh264 (from third_party/openh264) and ffmpeg_branding (from third_party/ffmpeg).
These will be used in a follow-up CL that adds an encoder and decoder implementation.
The flags are added in this CL so that they can be used by trybots/waterfall bots in GN without "Build argument had no effect" errors. Equivalent GYP changes are also added.

BUG=468365

Review URL: https://codereview.webrtc.org/1575913003

Cr-Commit-Position: refs/heads/master@{#11204}

.gitignore

@@ -91,6 +91,7 @@
 /third_party/directxsdk
 /third_party/drmemory
 /third_party/expat
+/third_party/ffmpeg
 /third_party/gaeunit
 /third_party/gflags/src
 /third_party/google-visualization-python
@@ -121,6 +122,7 @@
 /third_party/nss
 /third_party/oauth2
 /third_party/ocmock
+/third_party/openh264
 /third_party/openmax_dl
 /third_party/opus
 /third_party/proguard

.gn

@@ -43,6 +43,7 @@ exec_script_whitelist = [
   "//build/toolchain/mac/BUILD.gn",
   "//build/toolchain/win/BUILD.gn",
   "//third_party/boringssl/BUILD.gn",
+  "//third_party/openh264/BUILD.gn",
   "//third_party/opus/BUILD.gn",
   "//webrtc/modules/video_render/BUILD.gn",
 ]

setup_links.py

@@ -40,6 +40,7 @@ DIRECTORIES = [
   'third_party/colorama',
   'third_party/drmemory',
   'third_party/expat',
+  'third_party/ffmpeg',
   'third_party/instrumented_libraries',
   'third_party/jsoncpp',
   'third_party/libc++-static',
@@ -53,6 +54,7 @@ DIRECTORIES = [
   'third_party/lss',
   'third_party/nss',
   'third_party/ocmock',
+  'third_party/openh264',
   'third_party/openmax_dl',
   'third_party/opus',
   'third_party/proguard',

sync_chromium.py

@@ -31,7 +31,7 @@ import textwrap
 
 # Bump this whenever the algorithm changes and you need bots/devs to re-sync,
 # ignoring the .last_sync_chromium file
-SCRIPT_VERSION = 5
+SCRIPT_VERSION = 6
 
 ROOT_DIR = os.path.dirname(os.path.abspath(__file__))
 CHROMIUM_NO_HISTORY = 'CHROMIUM_NO_HISTORY'

webrtc/build/common.gypi

@@ -123,6 +123,17 @@
     # Enabling this may break interop with Android clients that support H264.
     'use_objc_h264%': 0,
 
+    # Enable this to build H.264 encoder/decoder using third party libraries.
+    # Encoding uses OpenH264 and decoding uses FFmpeg. Because of this, OpenH264
+    # and FFmpeg have to be correctly enabled separately.
+    # - use_openh264=1 is required for OpenH264 targets to be defined.
+    # - ffmpeg_branding=Chrome is one way to support H.264 decoding in FFmpeg.
+    #   FFmpeg can be built with/without H.264 support, see 'ffmpeg_branding'.
+    #   Without it, it compiles but H264DecoderImpl fails to initialize.
+    # CHECK THE OPENH264, FFMPEG AND H.264 LICENSES/PATENTS BEFORE BUILDING.
+    # http://www.openh264.org, https://www.ffmpeg.org/
+    'use_third_party_h264%': 0,  # TODO(hbos): To be used in follow-up CL(s).
+
     'conditions': [
       ['build_with_chromium==1', {
         # Exclude pulse audio on Chromium since its prerequisites don't require

webrtc/build/webrtc.gni

@@ -90,6 +90,17 @@ declare_args() {
   # Enable this to use HW H.264 encoder/decoder on iOS PeerConnections.
   # Enabling this may break interop with Android clients that support H264.
   rtc_use_objc_h264 = false
+
+  # Enable this to build H.264 encoder/decoder using third party libraries.
+  # Encoding uses OpenH264 and decoding uses FFmpeg. Because of this, OpenH264
+  # and FFmpeg have to be correctly enabled separately.
+  # - use_openh264=true is required for OpenH264 targets to be defined.
+  # - ffmpeg_branding="Chrome" is one way to support H.264 decoding in FFmpeg.
+  #   FFmpeg can be built with/without H.264 support, see 'ffmpeg_branding'.
+  #   Without it, it compiles but H264DecoderImpl fails to initialize.
+  # CHECK THE OPENH264, FFMPEG AND H.264 LICENSES/PATENTS BEFORE BUILDING.
+  # http://www.openh264.org, https://www.ffmpeg.org/
+  use_third_party_h264 = false  # TODO(hbos): To be used in follow-up CL(s).
 }
 
 # Make it possible to provide custom locations for some libraries (move these

webrtc/modules/video_coding/BUILD.gn

@@ -136,6 +136,18 @@ source_set("webrtc_h264") {
   deps = [
     "../../system_wrappers",
   ]
+
+  if (use_third_party_h264) {
+    # Dependency added so that variables use_openh264 and ffmpeg_branding are
+    # recognized build arguments (avoid "Build argument has no effect" error).
+    # The variables and dependencies will be used for real as soon as
+    # https://codereview.webrtc.org/1306813009/ lands. In the meantime, the
+    # build arguments are to be used by waterfall/trybots.
+    deps += [
+      "//third_party/ffmpeg:ffmpeg",
+      "//third_party/openh264:encoder",
+    ]
+  }
 }
 
 # TODO(tkchin): Source set for webrtc_h264_video_toolbox. Currently not