Adds dynamic audio rate control option

When DRC is on, game syncs to frame rate instead of audio buffer
capacity. Audio is resampled to generate more samples when buffer is
low and less when buffer is high, to keep buffer 40%-60% full. Buffer
size doubled to keep same avg. audio latency value.

Audio can distort when buffer is out of range, not often during
gameplay. Better resampler could improve but would be slower. When
buffer is always out of range (heavy frameskip), it is better to leave
off, DRC doesn't help anyway then.

Idea from RetroArch audio_driver.c and
https://near.sh/articles/audio/dynamic-rate-control

1 files changed, 7 insertions, 1 deletions

diff --git a/main.c b/main.c
index af55f0f..e91b832 100644
--- a/main.c
+++ b/main.c
@@ -31,6 +31,8 @@ static int last_screenshot = 0;
 static uint32_t vsyncs;
 static uint32_t renders;
 
+#define UNDERRUN_THRESHOLD 0.5
+
 static void toggle_fast_forward(int force_off)
 {
 	static int frameskip_style_was;
@@ -198,6 +200,7 @@ void set_defaults(void)
 	show_hud = 1;
 	limit_frames = 1;
 	enable_audio = 1;
+	enable_drc = 1;
 	audio_buffer_size = 5;
 	scale_size = SCALE_SIZE_NONE;
 	scale_filter = SCALE_FILTER_NEAREST;
@@ -496,7 +499,10 @@ static void adjust_audio(void) {
 
 	if (current_core.retro_audio_buffer_status) {
 		float occupancy = 1.0 - plat_sound_capacity();
-		current_core.retro_audio_buffer_status(true, (int)(occupancy * 100), occupancy < 0.50);
+		if (enable_drc)
+			occupancy = MIN(1.0, occupancy * 2.0);
+
+		current_core.retro_audio_buffer_status(true, (int)(occupancy * 100), occupancy < UNDERRUN_THRESHOLD);
 	}
 }