GBA Audio: Better audio resampling via FFmpeg

CHANGES

@@ -3,6 +3,7 @@ Features:
  - Support for gamepad axes, e.g. analog sticks or triggers
  - Add scale presets for up to 6x
  - Debugger: Add CLI "frame", frame advance command
+ - Better audio resampling via FFmpeg
 Bugfixes:
  - Qt: Fix issue with set frame sizes being the wrong height
  - Qt: Fix emulator crashing when full screen if a game is not running

CMakeLists.txt

@@ -156,6 +156,7 @@ if(USE_FFMPEG)
 	include_directories(AFTER ${LIBAVCODEC_INCLUDE_DIRS} ${LIBAVFORMAT_INCLUDE_DIRS} ${LIBAVRESAMPLE_INCLUDE_DIRS} ${LIBAVUTIL_INCLUDE_DIRS} ${LIBSWSCALE_INCLUDE_DIRS})
 	link_directories(${LIBAVCODEC_LIBRARY_DIRS} ${LIBAVFORMAT_LIBRARY_DIRS} ${LIBAVRESAMPLE_LIBRARY_DIRS} ${LIBAVUTIL_LIBRARY_DIRS} ${LIBSWSCALE_LIBRARY_DIRS})
 	list(APPEND UTIL_SRC "${CMAKE_SOURCE_DIR}/src/platform/ffmpeg/ffmpeg-encoder.c")
+	list(APPEND UTIL_SRC "${CMAKE_SOURCE_DIR}/src/platform/ffmpeg/ffmpeg-resample.c")
 	string(REGEX MATCH "^[0-9]+" LIBAVCODEC_VERSION_MAJOR ${libavcodec_VERSION})
 	string(REGEX MATCH "^[0-9]+" LIBAVFORMAT_VERSION_MAJOR ${libavformat_VERSION})
 	string(REGEX MATCH "^[0-9]+" LIBAVRESAMPLE_VERSION_MAJOR ${libavresample_VERSION})
@@ -255,6 +256,7 @@ message(STATUS "	Video recording: ${USE_FFMPEG}")
 message(STATUS "	GIF recording: ${USE_MAGICK}")
 message(STATUS "	Screenshot/advanced savestate support: ${USE_PNG}")
 message(STATUS "	ZIP support: ${USE_LIBZIP}")
+message(STATUS "	Better audio resampling: ${USE_FFMPEG}")
 message(STATUS "Frontend summary:")
 message(STATUS "	Qt: ${BUILD_QT}")
 message(STATUS "	SDL (${SDL_VERSION}): ${BUILD_SDL}")

src/platform/ffmpeg/ffmpeg-resample.c

@@ -0,0 +1,53 @@
+/* Copyright (c) 2013-2014 Jeffrey Pfau
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+#include "ffmpeg-resample.h"
+
+#include "gba-audio.h"
+
+#include <libavresample/avresample.h>
+#include <libavutil/opt.h>
+
+struct AVAudioResampleContext* GBAAudioOpenLAVR(struct GBAAudio* audio, unsigned outputRate) {
+	AVAudioResampleContext *avr = avresample_alloc_context();
+	av_opt_set_int(avr, "in_channel_layout", AV_CH_LAYOUT_STEREO, 0);
+	av_opt_set_int(avr, "out_channel_layout", AV_CH_LAYOUT_STEREO, 0);
+	av_opt_set_int(avr, "in_sample_rate", audio->sampleRate, 0);
+	av_opt_set_int(avr, "out_sample_rate", outputRate, 0);
+	av_opt_set_int(avr, "in_sample_fmt", AV_SAMPLE_FMT_S16P, 0);
+	av_opt_set_int(avr, "out_sample_fmt", AV_SAMPLE_FMT_S16, 0);
+	if (avresample_open(avr)) {
+		avresample_free(&avr);
+		return 0;
+	}
+	return avr;
+}
+
+unsigned GBAAudioResampleLAVR(struct GBAAudio* audio, struct AVAudioResampleContext* avr, struct GBAStereoSample* output, unsigned nSamples) {
+	int16_t left[GBA_AUDIO_SAMPLES];
+	int16_t right[GBA_AUDIO_SAMPLES];
+	int16_t* samples[2] = { left, right };
+
+	size_t totalRead = 0;
+	size_t available = avresample_available(avr);
+	if (available) {
+		totalRead = avresample_read(avr, (uint8_t**) &output, nSamples);
+		nSamples -= totalRead;
+		output += totalRead;
+	}
+	while (nSamples) {
+		unsigned read = GBAAudioCopy(audio, left, right, GBA_AUDIO_SAMPLES);
+
+		size_t currentRead = avresample_convert(avr, (uint8_t**) &output, nSamples * sizeof(struct GBAStereoSample), nSamples, (uint8_t**) samples, sizeof(left), read);
+		nSamples -= currentRead;
+		output += currentRead;
+		totalRead += currentRead;
+		if (read < GBA_AUDIO_SAMPLES && nSamples) {
+			memset(output, 0, nSamples * sizeof(struct GBAStereoSample));
+			break;
+		}
+	}
+	return totalRead;
+}

src/platform/ffmpeg/ffmpeg-resample.h

@@ -0,0 +1,16 @@
+/* Copyright (c) 2013-2014 Jeffrey Pfau
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+#ifndef FFMPEG_RESAMPLE
+#define FFMPEG_RESAMPLE
+
+struct AVAudioResampleContext;
+struct GBAAudio;
+struct GBAStereoSample;
+
+struct AVAudioResampleContext* GBAAudioOpenLAVR(struct GBAAudio* audio, unsigned outputRate);
+unsigned GBAAudioResampleLAVR(struct GBAAudio* audio, struct AVAudioResampleContext* avr, struct GBAStereoSample* output, unsigned nSamples);
+
+#endif

src/platform/sdl/sdl-audio.c

@@ -8,6 +8,11 @@
 #include "gba.h"
 #include "gba-thread.h"
 
+#ifdef USE_FFMPEG
+#include "platform/ffmpeg/ffmpeg-resample.h"
+#include <libavresample/avresample.h>
+#endif
+
 #define BUFFER_SIZE (GBA_AUDIO_SAMPLES >> 2)
 
 static void _GBASDLAudioCallback(void* context, Uint8* data, int len);
@@ -24,7 +29,9 @@ bool GBASDLInitAudio(struct GBASDLAudio* context, struct GBAThread* threadContex
 	context->desiredSpec.samples = context->samples;
 	context->desiredSpec.callback = _GBASDLAudioCallback;
 	context->desiredSpec.userdata = context;
+#ifndef USE_FFMPEG
 	context->drift = 0.f;
+#endif
 	if (SDL_OpenAudio(&context->desiredSpec, &context->obtainedSpec) < 0) {
 		GBALog(0, GBA_LOG_ERROR, "Could not open SDL sound system");
 		return false;
@@ -35,6 +42,10 @@ bool GBASDLInitAudio(struct GBASDLAudio* context, struct GBAThread* threadContex
 		threadContext->audioBuffers = context->samples * 2;
 	}
 
+#ifdef USE_FFMPEG
+	context->avr = 0;
+#endif
+
 	SDL_PauseAudio(0);
 	return true;
 }
@@ -44,6 +55,9 @@ void GBASDLDeinitAudio(struct GBASDLAudio* context) {
 	SDL_PauseAudio(1);
 	SDL_CloseAudio();
 	SDL_QuitSubSystem(SDL_INIT_AUDIO);
+#ifdef USE_FFMPEG
+	avresample_free(&context->avr);
+#endif
 }
 
 void GBASDLPauseAudio(struct GBASDLAudio* context) {
@@ -62,6 +76,7 @@ static void _GBASDLAudioCallback(void* context, Uint8* data, int len) {
 		memset(data, 0, len);
 		return;
 	}
+#ifndef USE_FFMPEG
 	audioContext->ratio = GBAAudioCalculateRatio(&audioContext->thread->gba->audio, audioContext->thread->fpsTarget, audioContext->obtainedSpec.freq);
 	if (audioContext->ratio == INFINITY) {
 		memset(data, 0, len);
@@ -72,4 +87,16 @@ static void _GBASDLAudioCallback(void* context, Uint8* data, int len) {
 	if (audioContext->obtainedSpec.channels == 2) {
 		GBAAudioResampleNN(&audioContext->thread->gba->audio, audioContext->ratio, &audioContext->drift, ssamples, len);
 	}
+#else
+	if (!audioContext->avr) {
+		if (!audioContext->thread->gba->audio.sampleRate) {
+			memset(data, 0, len);
+			return;
+		}
+		audioContext->avr = GBAAudioOpenLAVR(&audioContext->thread->gba->audio, audioContext->obtainedSpec.freq);
+	}
+	struct GBAStereoSample* ssamples = (struct GBAStereoSample*) data;
+	len /= 2 * audioContext->obtainedSpec.channels;
+	GBAAudioResampleLAVR(&audioContext->thread->gba->audio, audioContext->avr, ssamples, len);
+#endif
 }

src/platform/sdl/sdl-audio.h

@@ -17,8 +17,12 @@ struct GBASDLAudio {
 	// State
 	SDL_AudioSpec desiredSpec;
 	SDL_AudioSpec obtainedSpec;
+#ifndef USE_FFMPEG
 	float drift;
 	float ratio;
+#else
+	struct AVAudioResampleContext* avr;
+#endif
 
 	struct GBAThread* thread;
 };