desktop: Improve animation sync

The timing on desktop was causing the movie to run too slow,
causing it to get out of sync. Now it should run at the correct
speed.

core/src/player.rs

@@ -236,6 +236,20 @@ impl<Audio: AudioBackend, Renderer: RenderBackend, Navigator: NavigatorBackend>
         }
     }
 
+    /// Returns the approximate duration of time until the next frame is due to run.
+    /// This is only an approximation to be used for sleep durations.
+    pub fn time_til_next_frame(&self) -> std::time::Duration {
+        let frame_time = 1000.0 / self.frame_rate;
+        let dt = if self.frame_accumulator <= 0.0 {
+            frame_time
+        } else if self.frame_accumulator >= frame_time {
+            0.0
+        } else {
+            frame_time - self.frame_accumulator
+        };
+        std::time::Duration::from_micros(dt as u64 * 1000)
+    }
+
     pub fn is_playing(&self) -> bool {
         self.is_playing
     }

desktop/src/main.rs

@@ -9,7 +9,7 @@ use glutin::{
 };
 use ruffle_core::{backend::render::RenderBackend, Player};
 use std::path::PathBuf;
-use std::time::{Duration, Instant};
+use std::time::Instant;
 use structopt::StructOpt;
 
 #[derive(StructOpt, Debug)]
@@ -119,12 +119,13 @@ fn run_player(input_path: PathBuf) -> Result<(), Box<dyn std::error::Error>> {
         }
 
         let new_time = Instant::now();
-        let dt = new_time.duration_since(time).as_millis();
+        let dt = new_time.duration_since(time).as_micros();
+        if dt > 0 {
             time = new_time;
+            player.tick(dt as f64 / 1000.0);
+        }
 
-        player.tick(dt as f64);
+        std::thread::sleep(player.time_til_next_frame());
-
-        std::thread::sleep(Duration::from_millis(1000 / 60));
     }
     Ok(())
 }