Bug 1392961 - Add preference to make VP9 the preferred video codec. r=jesup

Behaviour is controlled through the media.navigator.video.vp9_preferred preference.

MozReview-Commit-ID: J06ArFYNmTk

--HG--
extra : rebase_source : a25bd4783fde0acf8291ee440745a619d3fa7db8

media/webrtc/signaling/src/peerconnection/PeerConnectionImpl.cpp

@@ -833,7 +833,8 @@ class ConfigureCodec {
       mHardwareH264Supported(false),
       mSoftwareH264Enabled(false),
       mH264Enabled(false),
-      mVP9Enabled(false),
+      mVP9Enabled(true),
+      mVP9Preferred(false),
       mH264Level(13), // minimum suggested for WebRTC spec
       mH264MaxBr(0), // Unlimited
       mH264MaxMbps(0), // Unlimited
@@ -859,6 +860,9 @@ class ConfigureCodec {
       branch->GetBoolPref("media.peerconnection.video.vp9_enabled",
           &mVP9Enabled);
 
+      branch->GetBoolPref("media.peerconnection.video.vp9_preferred",
+          &mVP9Preferred);
+
       branch->GetIntPref("media.navigator.video.max_fs", &mVP8MaxFs);
       if (mVP8MaxFs <= 0) {
         mVP8MaxFs = 12288; // We must specify something other than 0
@@ -930,9 +934,14 @@ class ConfigureCodec {
             } else if (videoCodec.mName == "ulpfec") {
               videoCodec.mEnabled = mRedUlpfecEnabled;
             } else if (videoCodec.mName == "VP8" || videoCodec.mName == "VP9") {
-              if (videoCodec.mName == "VP9" && !mVP9Enabled) {
-                videoCodec.mEnabled = false;
-                break;
+              if (videoCodec.mName == "VP9") {
+                if (!mVP9Enabled) {
+                  videoCodec.mEnabled = false;
+                  break;
+                }
+                if (mVP9Preferred) {
+                  videoCodec.mStronglyPreferred = true;
+                }
               }
               videoCodec.mConstraints.maxFs = mVP8MaxFs;
               videoCodec.mConstraints.maxFps = mVP8MaxFr;
@@ -959,6 +968,7 @@ class ConfigureCodec {
     bool mSoftwareH264Enabled;
     bool mH264Enabled;
     bool mVP9Enabled;
+    bool mVP9Preferred;
     int32_t mH264Level;
     int32_t mH264MaxBr;
     int32_t mH264MaxMbps;

modules/libpref/init/all.js

@@ -485,6 +485,7 @@ pref("media.navigator.video.h264.max_br", 0);
 pref("media.navigator.video.h264.max_mbps", 0);
 pref("media.peerconnection.video.h264_enabled", false);
 pref("media.peerconnection.video.vp9_enabled", true);
+pref("media.peerconnection.video.vp9_preferred", false);
 pref("media.getusermedia.aec", 1);
 pref("media.getusermedia.browser.enabled", false);
 pref("media.getusermedia.channels", 0);