refactor: Use rational numbers for accurate frame rate calculations

Co-authored-by: aider (gemini/gemini-2.5-pro) <aider@aider.chat>

Cargo.toml

@@ -19,5 +19,6 @@ tokio = { version = "1", features = ["full"] }
 clap = { version = "4.4", features = ["derive"] }
 log = { version = "0.4", features = ["std"] }
 daemonize = "0.5.0"
+num-rational = "0.4"
 
 

src/api.rs

@@ -11,6 +11,8 @@ use std::sync::{Arc, Mutex};
 use crate::config::{self, Config};
 use crate::sync_logic::{self, LtcState};
 use crate::system;
+use num_rational::Ratio;
+use num_traits::ToPrimitive;
 
 // Data structure for the main status response
 #[derive(Serialize, Deserialize)]
@@ -48,7 +50,7 @@ async fn get_status(data: web::Data<AppState>) -> impl Responder {
         format!("{:02}:{:02}:{:02}:{:02}", f.hours, f.minutes, f.seconds, f.frames)
     });
     let frame_rate = state.latest.as_ref().map_or("…".to_string(), |f| {
-        format!("{:.2}fps", f.frame_rate)
+        format!("{:.2}fps", f.frame_rate.to_f64().unwrap_or(0.0))
     });
 
     let now_local = Local::now();
@@ -64,8 +66,9 @@ async fn get_status(data: web::Data<AppState>) -> impl Responder {
     let avg_delta = state.get_ewma_clock_delta();
     let mut delta_frames = 0;
     if let Some(frame) = &state.latest {
-        let frame_ms = 1000.0 / frame.frame_rate;
+        let delta_ms_ratio = Ratio::new(avg_delta, 1);
-        delta_frames = ((avg_delta as f64 / frame_ms).round()) as i64;
+        let frames_ratio = delta_ms_ratio * frame.frame_rate / Ratio::new(1000, 1);
+        delta_frames = frames_ratio.round().to_integer();
     }
 
     let sync_status = sync_logic::get_sync_status(avg_delta, &config);
@@ -239,7 +242,7 @@ mod tests {
                 minutes: 2,
                 seconds: 3,
                 frames: 4,
-                frame_rate: 25.0,
+                frame_rate: Ratio::new(25, 1),
                 timestamp: Utc::now(),
             }),
             lock_count: 10,

src/sync_logic.rs

@@ -129,8 +129,9 @@ impl LtcState {
     /// Convert average jitter into frames (rounded).
     pub fn average_frames(&self) -> i64 {
         if let Some(frame) = &self.latest {
-            let ms_per_frame = 1000.0 / frame.frame_rate;
+            let jitter_ms_ratio = Ratio::new(self.average_jitter(), 1);
-            (self.average_jitter() as f64 / ms_per_frame).round() as i64
+            let frames_ratio = jitter_ms_ratio * frame.frame_rate / Ratio::new(1000, 1);
+            frames_ratio.round().to_integer()
         } else {
             0
         }
@@ -192,7 +193,7 @@ mod tests {
             minutes: m,
             seconds: s,
             frames: 0,
-            frame_rate: 25.0,
+            frame_rate: Ratio::new(25, 1),
             timestamp: Utc::now(),
         }
     }

src/system.rs

@@ -1,6 +1,7 @@
 use crate::config::Config;
 use crate::sync_logic::LtcFrame;
 use chrono::{DateTime, Duration as ChronoDuration, Local, NaiveTime, TimeZone};
+use num_rational::Ratio;
 use std::process::Command;
 
 /// Check if Chrony is active
@@ -39,7 +40,8 @@ pub fn ntp_service_toggle(start: bool) {
 
 pub fn calculate_target_time(frame: &LtcFrame, config: &Config) -> DateTime<Local> {
     let today_local = Local::now().date_naive();
-    let ms = ((frame.frames as f64 / frame.frame_rate) * 1000.0).round() as u32;
+    let ms_ratio = Ratio::new(frame.frames as i64 * 1000, 1) / frame.frame_rate;
+    let ms = ms_ratio.round().to_integer() as u32;
     let timecode = NaiveTime::from_hms_milli_opt(frame.hours, frame.minutes, frame.seconds, ms)
         .expect("Invalid LTC timecode");
 
@@ -56,7 +58,8 @@ pub fn calculate_target_time(frame: &LtcFrame, config: &Config) -> DateTime<Loca
         + ChronoDuration::minutes(offset.minutes)
         + ChronoDuration::seconds(offset.seconds);
     // Frame offset needs to be converted to milliseconds
-    let frame_offset_ms = (offset.frames as f64 / frame.frame_rate * 1000.0).round() as i64;
+    let frame_offset_ms_ratio = Ratio::new(offset.frames * 1000, 1) / frame.frame_rate;
+    let frame_offset_ms = frame_offset_ms_ratio.round().to_integer();
     dt_local + ChronoDuration::milliseconds(frame_offset_ms + offset.milliseconds)
 }
 
@@ -163,6 +166,7 @@ mod tests {
     use super::*;
     use crate::config::TimeturnerOffset;
     use chrono::{Timelike, Utc};
+    use num_rational::Ratio;
 
     // Helper to create a test frame
     fn get_test_frame(h: u32, m: u32, s: u32, f: u32) -> LtcFrame {
@@ -172,7 +176,7 @@ mod tests {
             minutes: m,
             seconds: s,
             frames: f,
-            frame_rate: 25.0,
+            frame_rate: Ratio::new(25, 1),
             timestamp: Utc::now(),
         }
     }

src/ui.rs

@@ -19,9 +19,11 @@ use crossterm::{
 };
 
 use crate::config::Config;
-use get_if_addrs::get_if_addrs;
 use crate::sync_logic::{get_jitter_status, get_sync_status, LtcState};
 use crate::system;
+use get_if_addrs::get_if_addrs;
+use num_rational::Ratio;
+use num_traits::ToPrimitive;
 
 
 pub fn start_ui(
@@ -82,8 +84,9 @@ pub fn start_ui(
         if last_delta_update.elapsed() >= Duration::from_secs(1) {
             cached_delta_ms = avg_delta;
             if let Some(frame) = &state.lock().unwrap().latest {
-                let frame_ms = 1000.0 / frame.frame_rate;
+                let delta_ms_ratio = Ratio::new(avg_delta, 1);
-                cached_delta_frames = ((avg_delta as f64 / frame_ms).round()) as i64;
+                let frames_ratio = delta_ms_ratio * frame.frame_rate / Ratio::new(1000, 1);
+                cached_delta_frames = frames_ratio.round().to_integer();
             } else {
                 cached_delta_frames = 0;
             }
@@ -104,7 +107,7 @@ pub fn start_ui(
                 None => "LTC Timecode     : …".to_string(),
             };
             let fr_str = match opt {
-                Some(f) => format!("Frame Rate       : {:.2}fps", f.frame_rate),
+                Some(f) => format!("Frame Rate       : {:.2}fps", f.frame_rate.to_f64().unwrap_or(0.0)),
                 None => "Frame Rate       : …".to_string(),
             };
 

timeturner.py

@@ -9,10 +9,11 @@ import threading
 import queue
 import json
 from collections import deque
+from fractions import Fraction
 
 SERIAL_PORT = None
 BAUD_RATE = 115200
-FRAME_RATE = 25.0
+FRAME_RATE = Fraction(25, 1)
 CONFIG_PATH = "config.json"
 
 sync_pending = False
@@ -30,6 +31,14 @@ sync_enabled = False
 last_match_check = 0
 timecode_match_status = "UNKNOWN"
 
+def framerate_str_to_fraction(s):
+    if s == "23.98": return Fraction(24000, 1001)
+    if s == "24.00": return Fraction(24, 1)
+    if s == "25.00": return Fraction(25, 1)
+    if s == "29.97": return Fraction(30000, 1001)
+    if s == "30.00": return Fraction(30, 1)
+    return None
+
 def load_config():
     global hardware_offset_ms
     try:
@@ -50,13 +59,16 @@ def parse_ltc_line(line):
     if not match:
         return None
     status, hh, mm, ss, ff, fps = match.groups()
+    rate = framerate_str_to_fraction(fps)
+    if not rate:
+        return None
     return {
         "status": status,
         "hours": int(hh),
         "minutes": int(mm),
         "seconds": int(ss),
         "frames": int(ff),
-        "frame_rate": float(fps)
+        "frame_rate": rate
     }
 
 def serial_thread(port, baud, q):
@@ -154,7 +166,7 @@ def run_curses(stdscr):
                 parsed, arrival_time = latest_ltc
                 stdscr.addstr(3, 2, f"LTC Status   : {parsed['status']}")
                 stdscr.addstr(4, 2, f"LTC Timecode : {parsed['hours']:02}:{parsed['minutes']:02}:{parsed['seconds']:02}:{parsed['frames']:02}")
-                stdscr.addstr(5, 2, f"Frame Rate   : {FRAME_RATE:.2f}fps")
+                stdscr.addstr(5, 2, f"Frame Rate   : {float(FRAME_RATE):.2f}fps")
                 stdscr.addstr(6, 2, f"System Clock : {format_time(get_system_time())}")
 
                 if ltc_locked and sync_enabled and offset_history: