From b2c2c9353722a522f7a6fe5d5ff62c3e0649d8bd Mon Sep 17 00:00:00 2001
From: lifning <>
Date: Sat, 11 Dec 2021 03:10:39 -0800
Subject: [PATCH] experimental dynamic rate control feature in audio component
 (TBD: merge into SimpleSdl2Audio as an option)

---
 .../examples/multifunction_emulator.rs        |  2 +-
 .../src/provided/sdl2/audio_ratecontrol.rs    | 68 +++++++++++++------
 2 files changed, 50 insertions(+), 20 deletions(-)

diff --git a/ferretro_components/examples/multifunction_emulator.rs b/ferretro_components/examples/multifunction_emulator.rs
index f6282e1..5f19c06 100644
--- a/ferretro_components/examples/multifunction_emulator.rs
+++ b/ferretro_components/examples/multifunction_emulator.rs
@@ -99,7 +99,7 @@ pub fn main() -> Result<(), Box<dyn std::error::Error + Send + Sync>> {
         }
     }
 
-    emu.register_component(SimpleSdl2AudioComponent::new(&mut sdl_context)?)?;
+    emu.register_component(Sdl2RateControlledAudioComponent::new(&mut sdl_context)?)?;
 
     emu.register_component(SimpleSdl2KeyboardComponent::new(&mut sdl_context)?)?;
     emu.register_component(SimpleSdl2GamepadComponent::new(&mut sdl_context))?;
diff --git a/ferretro_components/src/provided/sdl2/audio_ratecontrol.rs b/ferretro_components/src/provided/sdl2/audio_ratecontrol.rs
index e464355..77b9af6 100644
--- a/ferretro_components/src/provided/sdl2/audio_ratecontrol.rs
+++ b/ferretro_components/src/provided/sdl2/audio_ratecontrol.rs
@@ -12,13 +12,22 @@ use super::audio::resample;
 
 pub struct Sdl2RateControlledAudioComponent {
     src_freq: f64,
+    ratio: f64,
     audio_buffer: Vec<i16>,
     queue: AudioQueue<i16>,
+    avg_headroom: f64,
+    started: bool,
 }
 
 impl RetroCallbacks for Sdl2RateControlledAudioComponent {
+    fn video_refresh(&mut self, _frame: &VideoFrame) {
+        self.started = true;
+    }
+
     fn audio_samples(&mut self, stereo_pcm: &[i16]) -> usize {
-        self.audio_buffer.extend(stereo_pcm);
+        if self.started {
+            self.audio_buffer.extend(stereo_pcm);
+        }
         stereo_pcm.len() / 2
     }
 
@@ -33,25 +42,47 @@ impl RetroCallbacks for Sdl2RateControlledAudioComponent {
 }
 
 impl RetroComponent for Sdl2RateControlledAudioComponent {
-    fn post_load_game(&mut self, _retro: &mut LibretroWrapper, _rom: &Path) -> Result<(), Box<dyn Error + Send + Sync>> {
+    fn post_load_game(&mut self, retro: &mut LibretroWrapper, _rom: &Path) -> Result<(), Box<dyn Error + Send + Sync>> {
+        self.src_freq = retro.get_system_av_info().timing.sample_rate;
         self.queue.resume();
+        self.started = false;
         Ok(())
     }
 
     fn post_run(&mut self, _retro: &mut LibretroWrapper) -> ControlFlow {
-        if let Ok(converter) = Self::make_converter(self.src_freq, self.queue.spec()) {
-            let mut samples = std::mem::take(&mut self.audio_buffer);
-            samples = resample(&converter, samples);
-            self.audio_buffer = samples;
-            self.queue.queue(&self.audio_buffer);
-            self.audio_buffer.clear();
+        if self.src_freq != 0.0 {
+            if self.started {
+                let sample_headroom = (self.queue.size() / 4) as f64;
+                self.avg_headroom = ((self.avg_headroom * 9.0) + sample_headroom) / 10.0;
+                self.avg_headroom /= 2.0;
+                let room = self.src_freq / 100.0;
+                let ratio_raw = ((room - self.avg_headroom) / room).clamp(-1.0, 1.0);
+                self.ratio = 1.0 + (ratio_raw * 0.01);
+            }
+            match Self::make_converter(self.src_freq * self.ratio, self.queue.spec()) {
+                Ok(converter) => {
+                    if !self.audio_buffer.is_empty() {
+                        let mut samples = std::mem::take(&mut self.audio_buffer);
+                        samples = resample(&converter, samples);
+                        self.audio_buffer = samples;
+                        self.queue.queue(&self.audio_buffer);
+                        self.audio_buffer.clear();
+                    }
+                    ControlFlow::Continue
+                }
+                Err(e) => {
+                    eprintln!("Audio sample rate conversion failed: {:?}", e);
+                    ControlFlow::Break
+                }
+            }
+        } else {
+            ControlFlow::Continue
         }
-        ControlFlow::Continue
     }
 }
 
 impl Sdl2RateControlledAudioComponent {
-    pub fn new(sdl_context: &mut Sdl, retro: &LibretroWrapper) -> Result<Self, Box<dyn std::error::Error>> {
+    pub fn new(sdl_context: &mut Sdl) -> crate::base::Result<Self> {
         let audio = sdl_context.audio().unwrap();
         let desired_spec = AudioSpecDesired {
             freq: None,
@@ -61,31 +92,30 @@ impl Sdl2RateControlledAudioComponent {
 
         let queue = AudioQueue::open_queue(&audio, None, &desired_spec)?;
 
-        let mut src_freq = retro.get_system_av_info().timing.sample_rate;
-        // HACK: some cores don't report this 'til we get an env call to set_system_av_info,
-        // so we can just default to the old libsnes default value.
-        if src_freq == 0.0 {
-            src_freq = 32040.5;
-        }
+        //  default to the old libsnes default value until after load_game or set_system_av_info.
+        let src_freq = 32040.5;
 
         Ok(Sdl2RateControlledAudioComponent {
             src_freq,
+            ratio: 1.0,
             audio_buffer: Default::default(),
             queue,
+            avg_headroom: 0.0,
+            started: false,
         })
     }
 
     fn make_converter(src_freq: f64, dest_spec: &AudioSpec) -> Result<AudioCVT, String> {
-        // note on the `* 64`: as long as the ratio between src_rate and dst_rate is right,
+        // note on the `* 16`: as long as the ratio between src_rate and dst_rate is right,
         // we should be in the clear -- this is to make up for SDL not giving us floats for
         // this, we can at least get some quasi-fixed-point precision going on...
         AudioCVT::new(
             AudioFormat::s16_sys(),
             2,
-            (src_freq * 64.0).round() as i32,
+            (src_freq * 16.0).round() as i32,
             dest_spec.format,
             dest_spec.channels,
-            dest_spec.freq * 64,
+            dest_spec.freq * 16,
         )
     }
 }