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fix: Correct clock drift for fractional frame rates

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Co-authored-by: aider (gemini/gemini-2.5-pro) <aider@aider.chat>
This commit is contained in:
Chris Frankland-Wright 2025-08-03 12:38:15 +01:00
parent 4ee791c817
commit 459500e402
1 changed files with 25 additions and 5 deletions
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30
src/system.rs
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@ -40,12 +40,32 @@ 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_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");
let naive_dt = today_local.and_time(timecode);
// Total seconds from timecode components
let timecode_secs =
frame.hours as i64 * 3600 + frame.minutes as i64 * 60 + frame.seconds as i64;
// Total duration in seconds as a rational number, including frames
let total_duration_secs =
Ratio::new(timecode_secs, 1) + Ratio::new(frame.frames as i64, 1) / frame.frame_rate;
// For fractional frame rates (23.98, 29.97), timecode runs slower than wall clock.
// We need to scale the timecode duration up to get wall clock time.
// The scaling factor is 1001/1000.
let scaled_duration_secs = if *frame.frame_rate.denom() == 1001 {
total_duration_secs * Ratio::new(1001, 1000)
} else {
total_duration_secs
};
// Convert to milliseconds
let total_ms = (scaled_duration_secs * Ratio::new(1000, 1))
.round()
.to_integer();
let naive_midnight = today_local.and_hms_opt(0, 0, 0).unwrap();
let naive_dt = naive_midnight + ChronoDuration::milliseconds(total_ms);
let mut dt_local = Local
.from_local_datetime(&naive_dt)
.single()