always search for plugins under install prefix

If pulseeffects was installed e.g. under /usr/local, gstreamer wouldn't
find the plugins that ship with it. Since some of these are actually
required, we ended up with a broken pipeline and no useful error
message.

meson.build

@@ -30,6 +30,7 @@ conf.set_quoted('GETTEXT_PACKAGE', meson.project_name())
 conf.set_quoted('LOCALE_DIR', localedir)
 conf.set_quoted('VERSION', meson.project_version())
 conf.set_quoted('PACKAGE', 'PulseEffects')
+conf.set_quoted('PLUGINS_INSTALL_DIR', join_paths(prefix, plugins_install_dir))
 
 configure_file(output: 'config.h', configuration: conf)
 

src/pipeline_base.cpp

@@ -6,6 +6,7 @@
 #include <mutex>
 #include "pipeline_base.hpp"
 #include "util.hpp"
+#include "config.h"
 
 namespace {
 
@@ -207,6 +208,8 @@ PipelineBase::PipelineBase(const std::string& tag, const uint& sampling_rate)
 
   // creating elements common to all pipelines
 
+  gst_registry_scan_path(gst_registry_get(), PLUGINS_INSTALL_DIR);
+
   source = gst_element_factory_make("pulsesrc", "source");
   capsfilter = gst_element_factory_make("capsfilter", nullptr);
   adapter = gst_element_factory_make("peadapter", nullptr);