Fix OCIO LUT async processor black screen and freeze

- Pass through input texture when the LUT processor is not ready yet,
  preventing black frames while the processor is being generated.
- Serialize processor generation with a single in-flight task to avoid
  concurrent OCIO lock contention that could freeze the UI.
- Invalidate cached frames after the async processor is set so the viewer
  refreshes automatically without requiring the playhead to be moved.
- Add OAK_DISABLE_HWACCEL environment variable to force software decoding.
- Add FFmpegDecoderHW regression test for H.264 4:2:2 10-bit decoding.

app/codec/ffmpeg/ffmpegdecoder.cpp

@@ -425,13 +425,17 @@ TexturePtr FFmpegDecoder::RetrieveVideoInternal(const RetrieveVideoParams &p)
 		AVFramePtr ptr = PreProcessFrame(f, p);
 		f=std::move(ptr);
 		if (!f) {
-			// Error occurred while software scaling
+			qWarning() << "PreProcessFrame failed";
 			return nullptr;
 		}
 
 		// Finally, perform any GPU processing required
 		TexturePtr texture = ProcessFrameIntoTexture(f, p, original);
 
+		if (!texture) {
+			qWarning() << "ProcessFrameIntoTexture returned null";
+		}
+
 		return texture;
 	}
 
@@ -1476,6 +1480,10 @@ bool FFmpegDecoder::Instance::Open(const char *filename, int stream_index)
 
 AVHWDeviceType FFmpegDecoder::Instance::ChooseHardwareDevice()
 {
+	if (qEnvironmentVariableIsSet("OAK_DISABLE_HWACCEL")) {
+		return AV_HWDEVICE_TYPE_NONE;
+	}
+
 #ifdef Q_OS_LINUX
 	// Prefer NVIDIA's NVDEC where available, then VAAPI/VDPAU.
 	for (AVHWDeviceType type : { AV_HWDEVICE_TYPE_CUDA, AV_HWDEVICE_TYPE_VAAPI,

app/node/color/ociobase/ociobase.cpp

@@ -63,13 +63,19 @@ void OCIOBaseNode::Value(const NodeValueRow &value, const NodeGlobals &globals,
 {
 	auto tex_met = value[kTextureInput];
 	TexturePtr t = tex_met.toTexture();
-	if (t && processor_) {
-		ColorTransformJob job;
+	if (t) {
+		if (processor_) {
+			ColorTransformJob job;
 
-		job.SetColorProcessor(processor_);
-		job.SetInputTexture(tex_met);
+			job.SetColorProcessor(processor_);
+			job.SetInputTexture(tex_met);
 
-		table->Push(NodeValue::kTexture, t->toJob(job), this);
+			table->Push(NodeValue::kTexture, t->toJob(job), this);
+		} else {
+			// Processor isn't ready yet (e.g. still being generated
+			// asynchronously), pass the input through unchanged.
+			table->Push(NodeValue::kTexture, QVariant::fromValue(t), this);
+		}
 	}
 }
 

app/node/color/ociolut/ociolut.cpp

@@ -154,10 +154,30 @@ void OCIOLutNode::GenerateProcessor()
 	pending_path_ = path;
 	pending_direction_ = direction;
 	pending_generation_++;
-	const int generation = pending_generation_;
-	ColorManager *manager = this->manager();
 
-	locker.unlock();
+	MaybeStartNextTask();
+}
+
+void OCIOLutNode::MaybeStartNextTask()
+{
+	if (task_running_) {
+		return;
+	}
+
+	if (pending_path_.isEmpty()) {
+		return;
+	}
+
+	if (pending_path_ == last_path_ && pending_direction_ == last_direction_ &&
+		last_processor_) {
+		return;
+	}
+
+	task_running_ = true;
+	const int generation = pending_generation_;
+	const QString path = pending_path_;
+	const int direction = pending_direction_;
+	ColorManager *manager = this->manager();
 
 	QThreadPool::globalInstance()->start(
 		new GenerateProcessorTask(this, path, direction, generation, manager));
@@ -169,12 +189,16 @@ void OCIOLutNode::SetProcessorResult(ColorProcessorPtr processor,
 {
 	QMutexLocker locker(&gen_mutex_);
 
+	task_running_ = false;
+
 	if (generation != pending_generation_) {
-		// A newer request was issued while this one was in flight; ignore.
+		// A newer request was issued while this one was in flight; restart.
+		MaybeStartNextTask();
 		return;
 	}
 
 	if (path != pending_path_ || direction != pending_direction_) {
+		MaybeStartNextTask();
 		return;
 	}
 
@@ -182,6 +206,9 @@ void OCIOLutNode::SetProcessorResult(ColorProcessorPtr processor,
 	last_direction_ = direction;
 	last_processor_ = processor;
 	set_processor(processor);
+
+	// The processor has changed, ensure any cached frames are re-rendered.
+	InvalidateAll(kTextureInput);
 }
 
 OCIOLutNode::GenerateProcessorTask::GenerateProcessorTask(

app/node/color/ociolut/ociolut.h

@@ -80,6 +80,7 @@ private:
 	};
 
 	void GenerateProcessor();
+	void MaybeStartNextTask();
 
 	QMutex gen_mutex_;
 	QString last_path_;
@@ -89,6 +90,7 @@ private:
 	QString pending_path_;
 	int pending_direction_ = -1;
 	int pending_generation_ = 0;
+	bool task_running_ = false;
 };
 
 } // namespace olive