Improved OMP/FFmpeg Thread Control (Settings)

src/OpenMPUtilities.h

@@ -20,9 +20,9 @@
 #include "Settings.h"
 
 // Calculate the # of OpenMP Threads to allow
-#define OPEN_MP_NUM_PROCESSORS std::min(omp_get_num_procs(), std::max(2, openshot::Settings::Instance()->OMP_THREADS))
-#define FF_VIDEO_NUM_PROCESSORS std::min(omp_get_num_procs(), std::max(2, openshot::Settings::Instance()->FF_THREADS))
-#define FF_AUDIO_NUM_PROCESSORS std::min(omp_get_num_procs(), std::max(2, openshot::Settings::Instance()->FF_THREADS))
+#define OPEN_MP_NUM_PROCESSORS openshot::Settings::Instance()->EffectiveOMPThreads()
+#define FF_VIDEO_NUM_PROCESSORS std::clamp(openshot::Settings::Instance()->FF_THREADS, 2, openshot::Settings::Instance()->MaxAllowedThreads())
+#define FF_AUDIO_NUM_PROCESSORS std::clamp(openshot::Settings::Instance()->FF_THREADS, 2, openshot::Settings::Instance()->MaxAllowedThreads())
 
 // Set max-active-levels to the max supported, if possible
 // (supported_active_levels is OpenMP 5.0 (November 2018) or later, only.)

src/Settings.cpp

@@ -10,6 +10,7 @@
 //
 // SPDX-License-Identifier: LGPL-3.0-or-later
 
+#include <algorithm>
 #include <cstdlib>
 #include <omp.h>
 #include "Settings.h"
@@ -19,18 +20,42 @@ using namespace openshot;
 // Global reference to Settings
 Settings *Settings::m_pInstance = nullptr;
 
+int Settings::EffectiveOMPThreads() const
+{
+	return std::clamp(OMP_THREADS, 2, MaxAllowedThreads());
+}
+
+int Settings::MaxAllowedThreads() const
+{
+	return std::max(2, std::max(2, omp_get_num_procs()) * 3);
+}
+
+void Settings::ApplyOpenMPSettings()
+{
+	const int requested_threads = EffectiveOMPThreads();
+	if (applied_omp_threads != requested_threads) {
+		omp_set_num_threads(requested_threads);
+		applied_omp_threads = requested_threads;
+	}
+}
+
 // Create or Get an instance of the settings singleton
 Settings *Settings::Instance()
 {
 	if (!m_pInstance) {
 		// Create the actual instance of Settings only once
 		m_pInstance = new Settings;
-		m_pInstance->OMP_THREADS = omp_get_num_procs();
-		m_pInstance->FF_THREADS = omp_get_num_procs();
+		const int machine_threads = std::max(2, omp_get_num_procs());
+		m_pInstance->default_omp_threads = machine_threads;
+		m_pInstance->default_ff_threads = machine_threads;
+		m_pInstance->OMP_THREADS = machine_threads;
+		m_pInstance->FF_THREADS = machine_threads;
 		auto env_debug = std::getenv("LIBOPENSHOT_DEBUG");
 		if (env_debug != nullptr)
 			m_pInstance->DEBUG_TO_STDERR = true;
 	}
 
+	m_pInstance->ApplyOpenMPSettings();
+
 	return m_pInstance;
 }

src/Settings.h

@@ -46,6 +46,15 @@ namespace openshot {
 		/// Private variable to keep track of singleton instance
 		static Settings * m_pInstance;
 
+		/// Last OMP thread count applied to the OpenMP runtime
+		int applied_omp_threads = 0;
+
+		/// Machine default OpenMP thread count detected at startup
+		int default_omp_threads = 2;
+
+		/// Machine default FFmpeg thread count detected at startup
+		int default_ff_threads = 2;
+
 	public:
 		/**
 		 * @brief Use video codec for faster video decoding (if supported)
@@ -64,8 +73,8 @@ namespace openshot {
 		/// Scale mode used in FFmpeg decoding and encoding (used as an optimization for faster previews)
 		bool HIGH_QUALITY_SCALING = false;
 
-		/// Number of threads of OpenMP
-		int OMP_THREADS = 16;
+		/// Number of OpenMP threads
+		int OMP_THREADS = 2;
 
 			/// Number of threads that ffmpeg uses
 			int FF_THREADS = 16;
@@ -116,6 +125,21 @@ namespace openshot {
  		/// Whether to dump ZeroMQ debug messages to stderr
 		bool DEBUG_TO_STDERR = false;
 
+		/// Return the effective OpenMP worker budget used by libopenshot heuristics
+		int EffectiveOMPThreads() const;
+
+		/// Return the maximum allowed thread override based on this machine
+		int MaxAllowedThreads() const;
+
+		/// Return the machine default OpenMP thread count detected at startup
+		int DefaultOMPThreads() const { return default_omp_threads; }
+
+		/// Return the machine default FFmpeg thread count detected at startup
+		int DefaultFFThreads() const { return default_ff_threads; }
+
+		/// Apply any explicit OpenMP thread override to the runtime
+		void ApplyOpenMPSettings();
+
 		/// Create or get an instance of this logger singleton (invoke the class with this method)
 		static Settings * Instance();
 	};

tests/Benchmark.cpp

@@ -9,12 +9,12 @@
 // SPDX-License-Identifier: LGPL-3.0-or-later
 
 #include <chrono>
-#include <cstdlib>
 #include <functional>
 #include <iostream>
 #include <string>
 #include <vector>
 
+#include "BenchmarkOptions.h"
 #include "Clip.h"
 #include "FFmpegReader.h"
 #include "FFmpegWriter.h"
@@ -26,6 +26,7 @@
 #include "QtImageReader.h"
 #endif
 #include "ReaderBase.h"
+#include "Settings.h"
 #include "Timeline.h"
 #include "effects/Brightness.h"
 #include "effects/ChromaKey.h"
@@ -62,24 +63,35 @@ int main(int argc, char* argv[]) {
 	const string video = base + "sintel_trailer-720p.mp4";
 	const string mask_img = base + "mask.png";
 	const string overlay = base + "front3.png";
-	string filter_test;
-	bool list_only = false;
+	benchmark::BenchmarkOptions options;
 	const int64_t chroma_bench_frames = 500;
 
-	for (int i = 1; i < argc; ++i) {
-		const string arg = argv[i];
-		if ((arg == "--test" || arg == "-t") && i + 1 < argc) {
-			filter_test = argv[++i];
-		} else if (arg == "--list" || arg == "-l") {
-			list_only = true;
-		} else if (arg == "--help" || arg == "-h") {
-			cout << "Usage: openshot-benchmark [--test <name>] [--list]\n";
-			return 0;
-		} else {
-			cerr << "Unknown argument: " << arg << "\n";
-			cerr << "Usage: openshot-benchmark [--test <name>] [--list]\n";
-			return 1;
-		}
+	try {
+		vector<string> args;
+		args.reserve(std::max(0, argc - 1));
+		for (int i = 1; i < argc; ++i)
+			args.emplace_back(argv[i]);
+		options = benchmark::ParseBenchmarkOptions(args);
+	} catch (const std::exception& e) {
+		cerr << e.what() << "\n";
+		cerr << benchmark::BenchmarkUsage() << "\n";
+		return 1;
+	}
+
+	if (options.show_help) {
+		cout << benchmark::BenchmarkUsage() << "\n";
+		return 0;
+	}
+
+	// Route benchmark thread settings through libopenshot's Settings singleton,
+	// matching how an application should configure the library before opening readers.
+	Settings *settings = Settings::Instance();
+	if (options.omp_threads > 0) {
+		settings->OMP_THREADS = options.omp_threads;
+		settings->ApplyOpenMPSettings();
+	}
+	if (options.ff_threads > 0) {
+		settings->FF_THREADS = options.ff_threads;
 	}
 
 	vector<Trial> trials;
@@ -278,7 +290,7 @@ int main(int argc, char* argv[]) {
 		r.Close();
 	});
 
-	if (list_only) {
+	if (options.list_only) {
 		for (const auto& trial : trials)
 			cout << trial.first << "\n";
 		return 0;
@@ -288,14 +300,14 @@ int main(int argc, char* argv[]) {
 	double total = 0.0;
 	int executed = 0;
 	for (const auto& trial : trials) {
-		if (!filter_test.empty() && trial.first != filter_test)
+		if (!options.filter_test.empty() && trial.first != options.filter_test)
 			continue;
 		total += time_trial(trial.first, trial.second);
 		executed++;
 	}
 
-	if (!filter_test.empty() && executed == 0) {
-		cerr << "Unknown test: " << filter_test << "\nAvailable tests:\n";
+	if (!options.filter_test.empty() && executed == 0) {
+		cerr << "Unknown test: " << options.filter_test << "\nAvailable tests:\n";
 		for (const auto& trial : trials)
 			cerr << "  " << trial.first << "\n";
 		return 2;

tests/BenchmarkArgs.cpp

@@ -0,0 +1,75 @@
+/**
+ * @file
+ * @brief Unit tests for benchmark CLI option parsing
+ * @author OpenShot Studios, LLC
+ *
+ * @ref License
+ */
+
+// Copyright (c) 2026 OpenShot Studios, LLC
+//
+// SPDX-License-Identifier: LGPL-3.0-or-later
+
+#include "openshot_catch.h"
+
+#include "BenchmarkOptions.h"
+
+using namespace openshot::benchmark;
+
+static void CHECK_RUNTIME_ERROR_CONTAINS(const std::vector<std::string>& args,
+										 const std::string& expected_fragment) {
+	try {
+		(void) ParseBenchmarkOptions(args);
+		FAIL("Expected ParseBenchmarkOptions() to throw std::runtime_error");
+	} catch (const std::runtime_error& e) {
+		CHECK(std::string(e.what()).find(expected_fragment) != std::string::npos);
+	} catch (...) {
+		FAIL("Expected std::runtime_error");
+	}
+}
+
+TEST_CASE("Benchmark usage string includes new thread flags", "[benchmark][args]") {
+	const std::string usage = BenchmarkUsage();
+	CHECK(usage.find("--omp-threads <n>") != std::string::npos);
+	CHECK(usage.find("--ff-threads <n>") != std::string::npos);
+}
+
+TEST_CASE("Benchmark args default correctly", "[benchmark][args]") {
+	const BenchmarkOptions options = ParseBenchmarkOptions({});
+	CHECK(options.filter_test.empty());
+	CHECK_FALSE(options.list_only);
+	CHECK_FALSE(options.show_help);
+	CHECK(options.omp_threads == 0);
+	CHECK(options.ff_threads == 0);
+}
+
+TEST_CASE("Benchmark args parse valid values", "[benchmark][args]") {
+	const BenchmarkOptions options = ParseBenchmarkOptions({
+		"--test", "Timeline",
+		"--list",
+		"--omp-threads", "12",
+		"--ff-threads", "16"
+	});
+
+	CHECK(options.filter_test == "Timeline");
+	CHECK(options.list_only);
+	CHECK_FALSE(options.show_help);
+	CHECK(options.omp_threads == 12);
+	CHECK(options.ff_threads == 16);
+}
+
+TEST_CASE("Benchmark args reject invalid thread values", "[benchmark][args]") {
+	CHECK_RUNTIME_ERROR_CONTAINS({"--omp-threads", "0"}, "Invalid --omp-threads value");
+	CHECK_RUNTIME_ERROR_CONTAINS({"--omp-threads", "1"}, "Invalid --omp-threads value");
+	CHECK_RUNTIME_ERROR_CONTAINS({"--omp-threads", "-1"}, "Invalid --omp-threads value");
+	CHECK_RUNTIME_ERROR_CONTAINS({"--ff-threads", "0"}, "Invalid --ff-threads value");
+	CHECK_RUNTIME_ERROR_CONTAINS({"--ff-threads", "1"}, "Invalid --ff-threads value");
+	CHECK_RUNTIME_ERROR_CONTAINS({"--ff-threads", "-1"}, "Invalid --ff-threads value");
+	CHECK_RUNTIME_ERROR_CONTAINS({"--omp-threads", "abc"}, "Invalid --omp-threads value");
+}
+
+TEST_CASE("Benchmark args reject missing values and unknown args", "[benchmark][args]") {
+	CHECK_RUNTIME_ERROR_CONTAINS({"--test"}, "Missing value for --test");
+	CHECK_RUNTIME_ERROR_CONTAINS({"--ff-threads"}, "Missing value for --ff-threads");
+	CHECK_RUNTIME_ERROR_CONTAINS({"--wat"}, "Unknown argument");
+}

tests/BenchmarkOptions.cpp

@@ -0,0 +1,76 @@
+/**
+ * @file
+ * @brief Shared benchmark CLI option parsing helpers
+ * @author OpenShot Studios, LLC
+ *
+ * @ref License
+ */
+
+// Copyright (c) 2026 OpenShot Studios, LLC
+//
+// SPDX-License-Identifier: LGPL-3.0-or-later
+
+#include "BenchmarkOptions.h"
+
+#include <stdexcept>
+
+namespace openshot {
+namespace benchmark {
+
+std::string BenchmarkUsage() {
+	return "Usage: openshot-benchmark [--test <name>] [--list] [--omp-threads <n>] [--ff-threads <n>]";
+}
+
+static int ParseThreadArg(const std::string& flag, const std::string& value) {
+	int parsed = 0;
+	try {
+		size_t consumed = 0;
+		parsed = std::stoi(value, &consumed);
+		if (consumed != value.size()) {
+			throw std::invalid_argument("extra characters");
+		}
+	} catch (const std::exception&) {
+		throw std::runtime_error("Invalid " + flag + " value: " + value + " (expected >= 2)");
+	}
+
+	if (parsed < 2) {
+		throw std::runtime_error("Invalid " + flag + " value: " + value + " (expected >= 2)");
+	}
+
+	return parsed;
+}
+
+BenchmarkOptions ParseBenchmarkOptions(const std::vector<std::string>& args) {
+	BenchmarkOptions options;
+
+	for (size_t i = 0; i < args.size(); ++i) {
+		const std::string& arg = args[i];
+		if (arg == "--test" || arg == "-t") {
+			if (i + 1 >= args.size()) {
+				throw std::runtime_error("Missing value for --test");
+			}
+			options.filter_test = args[++i];
+		} else if (arg == "--omp-threads") {
+			if (i + 1 >= args.size()) {
+				throw std::runtime_error("Missing value for --omp-threads");
+			}
+			options.omp_threads = ParseThreadArg("--omp-threads", args[++i]);
+		} else if (arg == "--ff-threads") {
+			if (i + 1 >= args.size()) {
+				throw std::runtime_error("Missing value for --ff-threads");
+			}
+			options.ff_threads = ParseThreadArg("--ff-threads", args[++i]);
+		} else if (arg == "--list" || arg == "-l") {
+			options.list_only = true;
+		} else if (arg == "--help" || arg == "-h") {
+			options.show_help = true;
+		} else {
+			throw std::runtime_error("Unknown argument: " + arg);
+		}
+	}
+
+	return options;
+}
+
+} // namespace benchmark
+} // namespace openshot