Doc cleanup

apps/LoopThroughWithOpenGLCompositing/videoio/VideoBackend.cpp

@@ -8,6 +8,7 @@
 
 #include <algorithm>
 #include <chrono>
+#include <cstdlib>
 #include <cstring>
 #include <cmath>
 #include <windows.h>
@@ -19,7 +20,8 @@ VideoBackend::VideoBackend(RenderEngine& renderEngine, HealthTelemetry& healthTe
 	mOutputProductionController(mPlayoutPolicy),
 	mReadyOutputQueue(mPlayoutPolicy),
 	mVideoIODevice(std::make_unique<DeckLinkSession>()),
-	mBridge(std::make_unique<OpenGLVideoIOBridge>(renderEngine))
+	mBridge(std::make_unique<OpenGLVideoIOBridge>(renderEngine)),
+	mInputCaptureDisabled(IsEnvironmentFlagEnabled("VST_DISABLE_INPUT_CAPTURE"))
 {
 }
 
@@ -69,6 +71,12 @@ bool VideoBackend::ConfigureInput(const VideoFormat& inputVideoMode, std::string
 {
 	if (mLifecycle.State() != VideoBackendLifecycleState::Configuring)
 		ApplyLifecycleTransition(VideoBackendLifecycleState::Configuring, "Configuring video backend input.");
+	if (mInputCaptureDisabled)
+	{
+		MutableState().hasInputSource = false;
+		MutableState().statusMessage = "DeckLink input capture disabled by VST_DISABLE_INPUT_CAPTURE for output timing isolation.";
+		return true;
+	}
 	if (!mVideoIODevice->ConfigureInput(
 		[this](const VideoIOFrame& frame) { HandleInputFrame(frame); },
 		inputVideoMode,
@@ -127,7 +135,7 @@ bool VideoBackend::Start()
 		return false;
 	}
 
-	if (!mVideoIODevice->StartInputStreams())
+	if (!mInputCaptureDisabled && !mVideoIODevice->StartInputStreams())
 	{
 		StopOutputProducerWorker();
 		StopOutputCompletionWorker();
@@ -198,6 +206,8 @@ bool VideoBackend::HasInputDevice() const
 
 bool VideoBackend::HasInputSource() const
 {
+	if (mInputCaptureDisabled)
+		return false;
 	return mVideoIODevice->HasInputSource();
 }
 
@@ -311,6 +321,9 @@ void VideoBackend::ReportNoInputDeviceSignalStatus()
 
 void VideoBackend::HandleInputFrame(const VideoIOFrame& frame)
 {
+	if (mInputCaptureDisabled)
+		return;
+
 	const VideoIOState& state = mVideoIODevice->State();
 	mHealthTelemetry.TryReportSignalStatus(!frame.hasNoInputSource, state.inputFrameSize.width, state.inputFrameSize.height, state.inputDisplayModeName);
 	PublishInputSignalChanged(frame, state);
@@ -1065,3 +1078,18 @@ std::string VideoBackend::PixelFormatName(VideoIOPixelFormat pixelFormat)
 {
 	return std::string(VideoIOPixelFormatName(pixelFormat));
 }
+
+bool VideoBackend::IsEnvironmentFlagEnabled(const char* name)
+{
+	if (name == nullptr || name[0] == '\0')
+		return false;
+
+	char* value = nullptr;
+	std::size_t valueSize = 0;
+	if (_dupenv_s(&value, &valueSize, name) != 0 || value == nullptr)
+		return false;
+
+	const std::string flag(value);
+	std::free(value);
+	return flag == "1" || flag == "true" || flag == "TRUE" || flag == "yes" || flag == "on";
+}