Bug 1305340 - Enable low-latency decoding on Windows 10 and later. r=pehrsons

Chrome has had it enabled for years, we had disabled it originally due to crashes seen on Windows 7.

Differential Revision: https://phabricator.services.mozilla.com/D23656

--HG--
extra : moz-landing-system : lando

dom/media/platforms/wmf/WMFVideoMFTManager.cpp

@@ -583,7 +583,10 @@ MediaResult WMFVideoMFTManager::InitInternal() {
     attr->GetUINT32(MF_SA_D3D_AWARE, &aware);
     attr->SetUINT32(CODECAPI_AVDecNumWorkerThreads,
                     WMFDecoderModule::GetNumDecoderThreads());
-    if (mLowLatency || gfxPrefs::PDMWMFLowLatencyEnabled()) {
+    bool lowLatency =
+        (gfxPrefs::PDMWMFLowLatencyEnabled() || IsWin10OrLater()) &&
+        !gfxPrefs::PDMWMFLowLatencyForceDisabled();
+    if (mLowLatency || lowLatency) {
       hr = attr->SetUINT32(CODECAPI_AVLowLatencyMode, TRUE);
       if (SUCCEEDED(hr)) {
         LOG("Enabling Low Latency Mode");

gfx/thebes/gfxPrefs.h

@@ -739,6 +739,7 @@ class gfxPrefs final {
   DECL_GFX_PREF(Live, "media.wmf.force.allow-p010-format", PDMWMFForceAllowP010Format, bool, false);
   DECL_GFX_PREF(Once, "media.wmf.use-sync-texture", PDMWMFUseSyncTexture, bool, true);
   DECL_GFX_PREF(Live, "media.wmf.low-latency.enabled", PDMWMFLowLatencyEnabled, bool, false);
+  DECL_GFX_PREF(Live, "media.wmf.low-latency.force-disabled", PDMWMFLowLatencyForceDisabled, bool, false);
   DECL_GFX_PREF(Live, "media.wmf.skip-blacklist", PDMWMFSkipBlacklist, bool, false);
   DECL_GFX_PREF(Live, "media.wmf.deblacklisting-for-telemetry-in-gpu-process", PDMWMFDeblacklistingForTelemetryInGPUProcess, bool, false);
   DECL_GFX_PREF(Live, "media.wmf.amd.highres.enabled", PDMWMFAMDHighResEnabled, bool, true);

modules/libpref/init/all.js

@@ -388,6 +388,7 @@ pref("media.wmf.dxva.enabled", true);
 pref("media.wmf.dxva.d3d11.enabled", true);
 pref("media.wmf.dxva.max-videos", 8);
 pref("media.wmf.low-latency.enabled", false);
+pref("media.wmf.low-latency.force-disabled", false);
 pref("media.wmf.amd.highres.enabled", true);
 pref("media.wmf.allow-unsupported-resolutions", false);
 pref("media.wmf.use-nv12-format", true);