diff --git a/automation/v4-docs/gui.txt b/automation/v4-docs/gui.txt
index f913e7040..83c145535 100644
--- a/automation/v4-docs/gui.txt
+++ b/automation/v4-docs/gui.txt
@@ -23,7 +23,7 @@ Returns: 1 number
 
 ---
 
-function aegisub.get_selection()
+function aegisub.gui.get_selection()
 
 Returns: 2 values, all numbers.
   1. Starting position of the selection.
diff --git a/meson.build b/meson.build
index 616c86053..7ef4edb52 100644
--- a/meson.build
+++ b/meson.build
@@ -224,9 +224,9 @@ foreach dep: [
     endif
 endforeach
 
-if host_machine.system() == 'windows' and get_option('avisynth').enabled()
+if get_option('avisynth').enabled()
     conf.set('WITH_AVISYNTH', 1) # bundled separately with installer
-    deps += cc.find_library('avifil32', required: true)
+    dep_avail += 'AviSynth'
 
     avs_opt = cmake.subproject_options()
     avs_opt.add_cmake_defines({
@@ -235,6 +235,10 @@ if host_machine.system() == 'windows' and get_option('avisynth').enabled()
 
     avs = cmake.subproject('avisynth', options: avs_opt)
     deps_inc += avs.include_directories('AviSynth-Headers')
+
+    if host_machine.system() == 'windows'
+      deps += cc.find_library('avifil32', required: true)
+    endif
 endif
 
 if host_machine.system() == 'windows' and not get_option('directsound').disabled()
diff --git a/src/ass_parser.cpp b/src/ass_parser.cpp
index e9e3c7899..33e878b71 100644
--- a/src/ass_parser.cpp
+++ b/src/ass_parser.cpp
@@ -100,7 +100,7 @@ public:
 						try_parse(parsed[2], &collapsed);
 						fold.collapsed = !!collapsed;
 
-						if (fold.start > 0 && fold.end > fold.start) {
+						if (fold.start >= 0 && fold.end > fold.start) {
 							folds.push_back(fold);
 						}
 					}
diff --git a/src/audio_provider_avs.cpp b/src/audio_provider_avs.cpp
index b94cb4df4..0daa77e8e 100644
--- a/src/audio_provider_avs.cpp
+++ b/src/audio_provider_avs.cpp
@@ -63,7 +63,7 @@ public:
 	bool NeedsCache() const override { return true; }
 };
 
-AvisynthAudioProvider::AvisynthAudioProvider(agi::fs::path const& filename) {
+AvisynthAudioProvider::AvisynthAudioProvider(agi::fs::path const& filename) try {
 	agi::acs::CheckFileRead(filename);
 
 	std::lock_guard<std::mutex> lock(avs_wrapper.GetMutex());
@@ -100,6 +100,9 @@ AvisynthAudioProvider::AvisynthAudioProvider(agi::fs::path const& filename) {
 			throw agi::AudioProviderError("Avisynth error: " + errmsg);
 	}
 }
+catch (AvisynthError& err) {
+	throw agi::AudioProviderError("Avisynth error: " + std::string(err.msg));
+}
 
 void AvisynthAudioProvider::LoadFromClip(AVSValue clip) {
 	// Check if it has audio
@@ -107,12 +110,15 @@ void AvisynthAudioProvider::LoadFromClip(AVSValue clip) {
 	if (!vi.HasAudio()) throw agi::AudioDataNotFound("No audio found.");
 
 	IScriptEnvironment *env = avs_wrapper.GetEnv();
+	AVSValue script;
 
 	// Convert to one channel
-	AVSValue script = env->Invoke(OPT_GET("Audio/Downmixer")->GetString().c_str(), clip);
+	std::string downmixtype = OPT_GET("Audio/Downmixer")->GetString();
+	if (downmixtype == "ConvertToMono" || downmixtype == "GetLeftChannel" || downmixtype == "GetRightChannel")
+		script = env->Invoke(downmixtype.c_str(), clip);
+	else
+		script = clip;
 
-	// Convert to 16 bits per sample
-	script = env->Invoke("ConvertAudioTo16bit", script);
 	vi = script.AsClip()->GetVideoInfo();
 
 	// Convert sample rate
@@ -132,8 +138,8 @@ void AvisynthAudioProvider::LoadFromClip(AVSValue clip) {
 	channels = vi.AudioChannels();
 	decoded_samples = num_samples = vi.num_audio_samples;
 	sample_rate = vi.SamplesPerSecond();
-	bytes_per_sample = vi.BytesPerAudioSample();
-	float_samples = false;
+	bytes_per_sample = vi.BytesPerChannelSample();
+	float_samples = vi.IsSampleType(SAMPLE_FLOAT);
 
 	this->clip = tempclip;
 }
diff --git a/src/avisynth_wrap.cpp b/src/avisynth_wrap.cpp
index fd2246f77..eb957fa3c 100644
--- a/src/avisynth_wrap.cpp
+++ b/src/avisynth_wrap.cpp
@@ -40,10 +40,24 @@
 
 #include <mutex>
 
+#ifndef _WIN32
+#include <dlfcn.h>
+#endif
+
+#ifdef _WIN32
+#define AVISYNTH_SO "avisynth.dll"
+#else
+#define AVISYNTH_SO "libavisynth.so"
+#endif
+
 // Allocate storage for and initialise static members
 namespace {
 	int avs_refcount = 0;
+#ifdef _WIN32
 	HINSTANCE hLib = nullptr;
+#else
+	void* hLib = nullptr;
+#endif
 	IScriptEnvironment *env = nullptr;
 	std::mutex AviSynthMutex;
 }
@@ -54,14 +68,26 @@ typedef IScriptEnvironment* __stdcall FUNC(int);
 
 AviSynthWrapper::AviSynthWrapper() {
 	if (!avs_refcount++) {
-		hLib = LoadLibrary(L"avisynth.dll");
+#ifdef _WIN32
+#define CONCATENATE(x, y) x ## y
+#define _Lstr(x) CONCATENATE(L, x)
+		hLib = LoadLibraryW(_Lstr(AVISYNTH_SO));
+#undef _Lstr
+#undef CONCATENATE
+#else
+		hLib = dlopen(AVISYNTH_SO, RTLD_LAZY | RTLD_LOCAL | RTLD_DEEPBIND);
+#endif
 
 		if (!hLib)
-			throw AvisynthError("Could not load avisynth.dll");
+			throw AvisynthError("Could not load " AVISYNTH_SO);
 
-		FUNC *CreateScriptEnv = (FUNC*)GetProcAddress(hLib, "CreateScriptEnvironment");
+#ifdef _WIN32
+		FUNC* CreateScriptEnv = (FUNC*)GetProcAddress(hLib, "CreateScriptEnvironment");
+#else
+		FUNC* CreateScriptEnv = (FUNC*)dlsym(hLib, "CreateScriptEnvironment");
+#endif
 		if (!CreateScriptEnv)
-			throw AvisynthError("Failed to get address of CreateScriptEnv from avisynth.dll");
+			throw AvisynthError("Failed to get address of CreateScriptEnv from " AVISYNTH_SO);
 
 		env = CreateScriptEnv(AVISYNTH_INTERFACE_VERSION);
 
@@ -79,9 +105,13 @@ AviSynthWrapper::AviSynthWrapper() {
 
 AviSynthWrapper::~AviSynthWrapper() {
 	if (!--avs_refcount) {
-		delete env;
-		AVS_linkage = nullptr;
+		env->DeleteScriptEnvironment();
+#ifdef _WIN32
 		FreeLibrary(hLib);
+#else
+		dlclose(hLib);
+#endif
+		AVS_linkage = nullptr;
 	}
 }
 
diff --git a/src/fold_controller.cpp b/src/fold_controller.cpp
index 56de5aaf4..ac1cd2084 100644
--- a/src/fold_controller.cpp
+++ b/src/fold_controller.cpp
@@ -104,7 +104,7 @@ void FoldController::MakeFoldsFromFile() {
 
 	int numlines = context->ass->Events.size();
 	for (LineFold fold : context->ass->Properties.folds) {
-		if (fold.start > 0 && fold.start < fold.end && fold.end <= numlines) {
+		if (fold.start >= 0 && fold.start < fold.end && fold.end <= numlines) {
 			auto opener = std::next(context->ass->Events.begin(), fold.start);
 			RawAddFold(*opener, *std::next(opener, fold.end - fold.start), fold.collapsed);
 		}
diff --git a/src/libresrc/default_config.json b/src/libresrc/default_config.json
index 7989b0fb1..fb6ea30b8 100644
--- a/src/libresrc/default_config.json
+++ b/src/libresrc/default_config.json
@@ -339,7 +339,7 @@
 			}
 		},
 		"Avisynth" : {
-			"Memory Max" : 128
+			"Memory Max" : 1024
 		},
 		"FFmpegSource" : {
 			"Cache" : {
diff --git a/src/libresrc/osx/default_config.json b/src/libresrc/osx/default_config.json
index ceee6db4e..05ae560ba 100644
--- a/src/libresrc/osx/default_config.json
+++ b/src/libresrc/osx/default_config.json
@@ -338,7 +338,7 @@
 			}
 		},
 		"Avisynth" : {
-			"Memory Max" : 128
+			"Memory Max" : 1024
 		},
 		"FFmpegSource" : {
 			"Cache" : {
diff --git a/src/meson.build b/src/meson.build
index 5287fb198..8e7e562c7 100644
--- a/src/meson.build
+++ b/src/meson.build
@@ -174,11 +174,8 @@ if host_machine.system() == 'darwin'
     )
 elif host_machine.system() == 'windows'
     aegisub_src += files(
-        'avisynth_wrap.cpp',
         'font_file_lister_gdi.cpp',
         # 'libass_gdi_fontselect.cpp',
-        'audio_provider_avs.cpp',
-        'video_provider_avs.cpp',
     )
 
     if cc.has_header('wingdi.h')
@@ -241,6 +238,10 @@ opt_src = [
                'video_provider_ffmpegsource.cpp',
                'ffmpegsource_common.cpp']],
 
+    ['AviSynth', ['avisynth_wrap.cpp',
+                  'audio_provider_avs.cpp',
+                  'video_provider_avs.cpp']],
+
     ['Hunspell', 'spellchecker_hunspell.cpp'],
 ]
 
diff --git a/src/preferences.cpp b/src/preferences.cpp
index 2a212cf69..6b445dc0a 100644
--- a/src/preferences.cpp
+++ b/src/preferences.cpp
@@ -399,8 +399,8 @@ void Advanced_Audio(wxTreebook *book, Preferences *parent) {
 
 #ifdef WITH_AVISYNTH
 	auto avisynth = p->PageSizer("Avisynth");
-	const wxString adm_arr[3] = { "ConvertToMono", "GetLeftChannel", "GetRightChannel" };
-	wxArrayString adm_choice(3, adm_arr);
+	const wxString adm_arr[4] = { "None", "ConvertToMono", "GetLeftChannel", "GetRightChannel" };
+	wxArrayString adm_choice(4, adm_arr);
 	p->OptionChoice(avisynth, _("Avisynth down-mixer"), adm_choice, "Audio/Downmixer");
 	p->OptionAdd(avisynth, _("Force sample rate"), "Provider/Audio/AVS/Sample Rate");
 #endif
diff --git a/src/video_provider_avs.cpp b/src/video_provider_avs.cpp
index dabcdaa68..7c779e800 100644
--- a/src/video_provider_avs.cpp
+++ b/src/video_provider_avs.cpp
@@ -93,7 +93,7 @@ public:
 	bool HasAudio() const override                 { return has_audio; }
 };
 
-AvisynthVideoProvider::AvisynthVideoProvider(agi::fs::path const& filename, std::string const& colormatrix) {
+AvisynthVideoProvider::AvisynthVideoProvider(agi::fs::path const& filename, std::string const& colormatrix) try {
 	agi::acs::CheckFileRead(filename);
 
 	std::lock_guard<std::mutex> lock(avs.GetMutex());
@@ -182,6 +182,9 @@ file_exit:
 		throw VideoOpenError("Avisynth error: " + std::string(err.msg));
 	}
 }
+catch (AvisynthError const& err) {
+	throw VideoProviderError("Avisynth error: " + std::string(err.msg));
+}
 
 void AvisynthVideoProvider::Init(std::string const& colormatrix) {
 	auto script = source_clip;