[webkit-dev] Trying to turn WebRTC's code on - MEDIA_STREAM flags

Eric Carlson eric.carlson at apple.com
Thu Nov 12 09:38:14 PST 2015

> On Jul 18, 2014, at 3:17 AM, Jacques-Olivier <jo.hache at temasys.com.sg> wrote:
> I’m new on this mailing so I’ll start by introducing myself:
> My name Jacques-Olivier Haché (J-O), I’m working for Temasys Communication, and I’m entering the WebKit project to work on the implementation of WebRTC inside WebKit.
> For those who would be following the WebRTC’s news, I’m also the main developer of the WebRTC plugin released by Temasys.

  Welcome to the WebKit community!

> I am now trying to enable the WebRTC related features to get a better understanding of the current state of this part of the project. 
> I have to say that I faced a lack of documentation on this area. I found the features list <https://trac.webkit.org/wiki/FeatureFlags>, a document about how to add a new feature <https://trac.webkit.org/wiki/AddingFeatures> but nothing about how to turn a feature on and off (there is actually a TODO about that in the second link).
> I looked into the files that one needs to change to add a new feature and found two interesting files:
> Source/WTF/wtf/FeatureDefines.h - where the WebRTC related contants were set to 0 instead of 1
> Source/cmake/WebKitFeatures.cmake - where the contants were set to OFF
> I listed the following definitions that look related to WebRTC
  This flag is for features in the HTML Media Capture spec: http://www.w3.org/TR/html-media-capture/

  This is for the JavaScript-based <audio> and <video> controls some ports us.

  This is for the Media Source Extension spec: http://www.w3.org/TR/media-source/
  This is for an experimental HTMLMediaElement statistics feature enabled by some ports.

  This is for the Media Capture and Streams spec: http://w3c.github.io/mediacapture-main/
  This is for <audio> and <video> in general.

  This is for WebVTT.

  You should not need to change any of these flags to build for the Mac.

> I turned those definitions to 1 and ON in the respective file and tried to build.
> The code in the header WebCore/Modules/mediastream/mediastream.h could not compile apparently because the observer did not have a destructor. I created one:
>     class Observer {
>     public:
>         virtual void didAddOrRemoveTrack() = 0;
>       virtual ~Observer() {};
>     };
  It sounds like your sources are not up to date, I fixed this in https://trac.webkit.org/r175066

> I now have a linking error that I do not understand when building WebCore with Xcode. 
> Ld 
> Undefined symbols for architecture x86_64:
>   "__ZN7WebCore11JSNavigator18webkitGetUserMediaEPN3JSC9ExecStateE", referenced from:
>       __ZN7WebCore46jsNavigatorPrototypeFunctionWebkitGetUserMediaEPN3JSC9ExecStateE in JSNavigator.o
>   "__ZN7WebCore15RTCOfferOptions6createERKNS_10DictionaryERi", referenced from:
> __ZN7WebCore17RTCPeerConnection11createOfferEN3WTF10PassRefPtrINS_29RTCSessionDescriptionCallbackEEENS2_INS_30RTCPeerConnectionErrorCallbackEEERKNS_10DictionaryERi in RTCPeerConnection.o
>   "__ZN7WebCore20MediaConstraintsMock17verifyConstraintsEN3WTF10PassRefPtrINS_16MediaConstraintsEEE", referenced from:
>       __ZN7WebCore21MockMediaStreamCenter26validateRequestConstraintsEN3WTF10PassRefPtrINS_25MediaStreamCreationClientEEENS2_INS_16MediaConstraintsEEES6_ in MockMediaStreamCenter.o
>       __ZN7WebCore21MockMediaStreamCenter17createMediaStreamEN3WTF10PassRefPtrINS_25MediaStreamCreationClientEEENS2_INS_16MediaConstraintsEEES6_ in MockMediaStreamCenter.o
>   "__ZN7WebCore21RTCOfferAnswerOptions6createERKNS_10DictionaryERi", referenced from:
>       __ZN7WebCore17RTCPeerConnection12createAnswerEN3WTF10PassRefPtrINS_29RTCSessionDescriptionCallbackEEENS2_INS_30RTCPeerConnectionErrorCallbackEEERKNS_10DictionaryERi in RTCPeerConnection.o
>   "__ZN7WebCore4toJSEPN3JSC9ExecStateEPNS_17JSDOMGlobalObjectEPNS_16RTCConfigurationE", referenced from:
>       __ZN7WebCore52jsRTCPeerConnectionPrototypeFunctionGetConfigurationEPN3JSC9ExecStateE in JSRTCPeerConnection.o
> ld: symbol(s) not found for architecture x86_64
> clang: error: linker command failed with exit code 1 (use -v to see invocation)
  I don’t get these errors when I build, I suspect they will go away for you when you update your sources to TOT.

> Is anyone used to turn the WebRTC code on and off?

  WebKit’s WebRTC implementation is currently in a state of flux, moving from a platform API that maps closely to the RTC JavaScript API to a more abstract interface will make it easier to use different backend libraries. See bugs https://webkit.org/b/150165 and https://webkit.org/b/150166 for example.


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