Allow disabling backend using environment variables.

src/nav_backend_androidndk.cpp

@@ -559,12 +559,16 @@ const char *AndroidNDKBackend::getInfo()
 
 Backend *create()
 {
+	if (checkBackendDisabled("ANDROIDNDK"))
+		return nullptr;
+
 	try
 	{
 		return new AndroidNDKBackend();
 	}
 	catch(const std::exception& e)
 	{
+		nav::error::set(e);
 		return nullptr;
 	}
 }

src/nav_backend_ffmpeg.cpp

@@ -933,6 +933,9 @@ const char *FFmpegBackend::getInfo()
 
 Backend *create()
 {
+	if (checkBackendDisabled("FFMPEG"))
+		return nullptr;
+
 	try
 	{
 		return new FFmpegBackend();

src/nav_backend_mediafoundation.cpp

@@ -879,12 +879,16 @@ const char *MediaFoundationBackend::getInfo()
 
 Backend *create()
 {
+	if (checkBackendDisabled("MEDIAFOUNDATION"))
+		return nullptr;
+
 	try
 	{
 		return new MediaFoundationBackend();
 	}
-	catch(const std::exception&)
+	catch(const std::exception &e)
 	{
+		nav::error::set(e);
 		return nullptr;
 	}
 }

src/nav_common.cpp

@@ -48,6 +48,22 @@ void *FrameVector::data() noexcept
 	return buffer.data();
 }
 
+bool checkBackendDisabled(const std::string &backendNameUppercase)
+{
+	std::string name = "NAV_DISABLE_" + backendNameUppercase;
+	const char *value = getenv(name.c_str());
+
+	return value != nullptr && (
+		strcmp(value, "1") == 0 ||
+		strcmp(value, "ON") == 0 ||
+		strcmp(value, "on") == 0 ||
+		strcmp(value, "On") == 0 ||
+		strcmp(value, "YES") == 0 ||
+		strcmp(value, "yes") == 0 ||
+		strcmp(value, "Yes") == 0
+	);
+}
+
 #ifdef _WIN32
 std::wstring fromUTF8(const std::string &str)
 {

src/nav_common.hpp

@@ -46,6 +46,8 @@ inline nav_audioformat makeAudioFormat(uint8_t bps, bool is_float, bool is_signe
 	return nav_audioformat(uint16_t(bps) | floatval | signedval);
 }
 
+bool checkBackendDisabled(const std::string &backendNameUppercase);
+
 #ifdef _WIN32
 std::wstring fromUTF8(const std::string &str);
 #endif /* _WIN32 */