From dabd9f699f4c4b6e3402ecb7c06f5b9518f08937 Mon Sep 17 00:00:00 2001
From: wangqr <wangqr@wangqr.tk>
Date: Thu, 26 Dec 2019 17:31:59 -0500
Subject: [PATCH] Add option to downmix FFMS audio

When enabled, restore FFMS to old behavior, downmixing auduo to S16 mono. This can reduce cache usage.

Fix wangqr/Aegisub#31
---
 src/audio_provider_ffmpegsource.cpp | 22 ++++++++++++----------
 src/libresrc/default_config.json    |  3 ++-
 src/preferences.cpp                 |  1 +
 src/project.cpp                     |  1 +
 4 files changed, 16 insertions(+), 11 deletions(-)

diff --git a/src/audio_provider_ffmpegsource.cpp b/src/audio_provider_ffmpegsource.cpp
index 0a201855a..176a0ad81 100644
--- a/src/audio_provider_ffmpegsource.cpp
+++ b/src/audio_provider_ffmpegsource.cpp
@@ -165,17 +165,19 @@ void FFmpegSourceAudioProvider::LoadAudio(agi::fs::path const& filename) {
 			throw agi::AudioProviderError("unknown or unsupported sample format");
 	}
 
-	if (channels > 1 || bytes_per_sample != 2) {
-		std::unique_ptr<FFMS_ResampleOptions, decltype(&FFMS_DestroyResampleOptions)>
-			opt(FFMS_CreateResampleOptions(AudioSource), FFMS_DestroyResampleOptions);
-		opt->ChannelLayout = FFMS_CH_FRONT_CENTER;
-		opt->SampleFormat = FFMS_FMT_S16;
+	if (OPT_GET("Provider/Audio/FFmpegSource/Downmix")->GetBool()) {
+		if (channels > 1 || bytes_per_sample != 2 || float_samples) {
+			std::unique_ptr<FFMS_ResampleOptions, decltype(&FFMS_DestroyResampleOptions)>
+				opt(FFMS_CreateResampleOptions(AudioSource), FFMS_DestroyResampleOptions);
+			opt->ChannelLayout = FFMS_CH_FRONT_CENTER;
+			opt->SampleFormat = FFMS_FMT_S16;
 
-		// Might fail if FFMS2 wasn't built with libavresample
-		if (!FFMS_SetOutputFormatA(AudioSource, opt.get(), nullptr)) {
-			channels = 1;
-			bytes_per_sample = 2;
-			float_samples = false;
+			// Might fail if FFMS2 wasn't built with libavresample
+			if (!FFMS_SetOutputFormatA(AudioSource, opt.get(), nullptr)) {
+				channels = 1;
+				bytes_per_sample = 2;
+				float_samples = false;
+			}
 		}
 	}
 }
diff --git a/src/libresrc/default_config.json b/src/libresrc/default_config.json
index 318f8d3ee..f5d26761b 100644
--- a/src/libresrc/default_config.json
+++ b/src/libresrc/default_config.json
@@ -331,7 +331,8 @@
 				"Sample Rate" : 0
 			},
 			"FFmpegSource" : {
-				"Decode Error Handling" : "ignore"
+				"Decode Error Handling" : "ignore",
+				"Downmix" : false
 			}
 		},
 		"Avisynth" : {
diff --git a/src/preferences.cpp b/src/preferences.cpp
index f6320dd75..91ebacee7 100644
--- a/src/preferences.cpp
+++ b/src/preferences.cpp
@@ -401,6 +401,7 @@ void Advanced_Audio(wxTreebook *book, Preferences *parent) {
 	p->OptionChoice(ffms, _("Audio indexing error handling mode"), error_modes_choice, "Provider/Audio/FFmpegSource/Decode Error Handling");
 
 	p->OptionAdd(ffms, _("Always index all audio tracks"), "Provider/FFmpegSource/Index All Tracks");
+	p->OptionAdd(ffms, _("Downmix to 16bit mono audio"), "Provider/Audio/FFmpegSource/Downmix");
 #endif
 
 #ifdef WITH_PORTAUDIO
diff --git a/src/project.cpp b/src/project.cpp
index e01dd3749..b6230af23 100644
--- a/src/project.cpp
+++ b/src/project.cpp
@@ -53,6 +53,7 @@ Project::Project(agi::Context *c) : context(c) {
 	OPT_SUB("Audio/Cache/Type", &Project::ReloadAudio, this);
 	OPT_SUB("Audio/Provider", &Project::ReloadAudio, this);
 	OPT_SUB("Provider/Audio/FFmpegSource/Decode Error Handling", &Project::ReloadAudio, this);
+	OPT_SUB("Provider/Audio/FFmpegSource/Downmix", &Project::ReloadAudio, this);
 	OPT_SUB("Provider/Avisynth/Allow Ancient", &Project::ReloadVideo, this);
 	OPT_SUB("Provider/Avisynth/Memory Max", &Project::ReloadVideo, this);
 	OPT_SUB("Provider/Video/FFmpegSource/Decoding Threads", &Project::ReloadVideo, this);