Further fixes to audio/video provider selection

- Fix selection not aborting when the preferred provider returns null
- Fix the default video provider being "ffmpegsource" (lowercase)
  instead of "FFmpegSource", which would trip up provider selection
- More generally, make sure the preferred video provider actually exists
  and fall back to the default (FFmpegSource) if not.

Fixes #23 .
Fixes #61 .
Fixes #83 .

src/audio_provider_factory.cpp

@@ -70,6 +70,11 @@ std::unique_ptr<agi::AudioProvider> SelectAudioProvider(fs::path const& filename
                                                         Path const& path_helper,
                                                         BackgroundRunner *br) {
 	auto preferred = OPT_GET("Audio/Provider")->GetString();
+
+	if (!std::any_of(std::begin(providers), std::end(providers), [&](factory provider) { return provider.name == preferred; })) {
+		preferred = OPT_GET("Audio/Provider")->GetDefaultString();
+	}
+
 	auto sorted = GetSorted(boost::make_iterator_range(std::begin(providers), std::end(providers)), preferred);
 
 	RearrangeWithPriority(sorted, filename);
@@ -84,9 +89,12 @@ std::unique_ptr<agi::AudioProvider> SelectAudioProvider(fs::path const& filename
 		std::string err;
 		try {
 			auto provider = factory->create(filename, br);
-			if (!provider) continue;
-			LOG_I("audio_provider") << "Using audio provider: " << factory->name;
-			return provider;
+			if (!provider) {
+				err = "Failed to create provider."; 	// Some generic error message here
+			} else {
+				LOG_I("audio_provider") << "Using audio provider: " << factory->name;
+				return provider;
+			}
 		}
 		catch (AudioDataNotFound const& ex) {
 			found_file = true;

src/libresrc/default_config.json

@@ -66,7 +66,7 @@
 		"Next Line on Commit" : true,
 		"Player" : "",
 		"Plays When Stepping Video" : false,
-		"Provider" : "ffmpegsource",
+		"Provider" : "FFmpegSource",
 		"Renderer" : {
 			"Spectrum" : {
 				"Cutoff" : 0,
@@ -660,7 +660,7 @@
 		"Last Script Resolution Mismatch Choice" : 2,
 		"Open Audio" : true,
 		"Overscan Mask" : false,
-		"Provider" : "ffmpegsource",
+		"Provider" : "FFmpegSource",
 		"Script Resolution Mismatch" : 1,
 		"Slider" : {
 			"Fast Jump Step" : 10,

src/libresrc/osx/default_config.json

@@ -66,7 +66,7 @@
 		"Next Line on Commit" : true,
 		"Player" : "",
 		"Plays When Stepping Video" : false,
-		"Provider" : "ffmpegsource",
+		"Provider" : "FFmpegSource",
 		"Renderer" : {
 			"Spectrum" : {
 				"Cutoff" : 0,
@@ -660,7 +660,7 @@
 		"Last Script Resolution Mismatch Choice" : 2,
 		"Open Audio" : true,
 		"Overscan Mask" : false,
-		"Provider" : "ffmpegsource",
+		"Provider" : "FFmpegSource",
 		"Script Resolution Mismatch" : 1,
 		"Slider" : {
 			"Fast Jump Step" : 10,

src/video_provider_manager.cpp

@@ -69,6 +69,11 @@ std::vector<std::string> VideoProviderFactory::GetClasses() {
 
 std::unique_ptr<VideoProvider> VideoProviderFactory::GetProvider(agi::fs::path const& filename, std::string const& colormatrix, agi::BackgroundRunner *br) {
 	auto preferred = OPT_GET("Video/Provider")->GetString();
+
+	if (!std::any_of(std::begin(providers), std::end(providers), [&](factory provider) { return provider.name == preferred; })) {
+		preferred = OPT_GET("Audio/Provider")->GetDefaultString();
+	}
+
 	auto sorted = GetSorted(boost::make_iterator_range(std::begin(providers), std::end(providers)), preferred);
 
 	RearrangeWithPriority(sorted, filename);
@@ -89,9 +94,12 @@ std::unique_ptr<VideoProvider> VideoProviderFactory::GetProvider(agi::fs::path c
 		std::string err;
 		try {
 			auto provider = factory->create(filename, colormatrix, br);
-			if (!provider) continue;
-			LOG_I("manager/video/provider") << factory->name << ": opened " << filename;
-			return finalize_provider(std::move(provider));
+			if (!provider) {
+				err = "Failed to create provider."; 	// Some generic error message here
+			} else {
+				LOG_I("manager/video/provider") << factory->name << ": opened " << filename;
+				return finalize_provider(std::move(provider));
+			}
 		}
 		catch (VideoNotSupported const& ex) {
 			found = true;