ZGaetano
3c689ccddf
The previous algorithm used `if (rem >= DROP)` (i.e. rem >= 4) to decide whether to advance to the next minute group. This fired immediately at frame 4, still inside minute 0 of the 10-minute non-drop group, producing 00:01:00;00 for what should be 00:00:00;04. Every timecode display in the editor was wrong for any position past the first four frames. Each 10-minute block has one 3600-frame non-drop minute followed by nine 3596-frame drop minutes. The fix checks `rem < FRAMES_FIRST_MIN` (3600) to identify the non-drop minute, then subtracts it before dividing into drop-minute slots. Frame labels within drop minutes are shifted by DROP (+4) so the first usable label is :00;04 as per SMPTE 12M.
93 lines
2.9 KiB
JavaScript
93 lines
2.9 KiB
JavaScript
// services/web-ui/public/js/timecode.js
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// 59.94 fps drop-frame timecode utilities.
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// Exposes: window.TC
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(function (global) {
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'use strict';
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// 59.94 = 60000/1001
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const FPS_EXACT = 60000 / 1001;
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const NOM = 60; // nominal integer fps
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const DROP = 4; // frames dropped per minute (except every 10th)
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const FRAMES_FIRST_MIN = NOM * 60; // 3600 – non-drop minute
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const FRAMES_PER_MIN = NOM * 60 - DROP; // 3596 – drop minute
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const FRAMES_PER_10MIN = FRAMES_PER_MIN * 10 + DROP; // 35964
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const FRAMES_PER_HOUR = FRAMES_PER_10MIN * 6; // 215784
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function pad2(n) { return String(Math.floor(n)).padStart(2, '0'); }
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/**
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* Convert a frame count to a 59.94 DF timecode string: HH:MM:SS;FF
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*
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* Each 10-minute group contains one non-drop minute (3600 frames) followed
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* by nine drop minutes (3596 frames each). Frame numbers 0–3 are skipped at
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* the start of every drop minute; we account for this by shifting the
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* within-minute frame index by DROP when computing ss/ff.
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*/
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function framesToTC(totalFrames) {
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const fc = Math.max(0, Math.round(totalFrames));
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const h = Math.floor(fc / FRAMES_PER_HOUR);
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let rem = fc % FRAMES_PER_HOUR;
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const tm = Math.floor(rem / FRAMES_PER_10MIN); // tens-of-minutes group (0–5)
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rem = rem % FRAMES_PER_10MIN;
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let m, ss, ff;
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if (rem < FRAMES_FIRST_MIN) {
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// First minute of the 10-min group — no frame drop
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m = 0;
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ss = Math.floor(rem / NOM);
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ff = rem % NOM;
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} else {
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// Minutes 1–9: frame numbers 0–3 at second :00 are skipped
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rem -= FRAMES_FIRST_MIN;
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m = Math.floor(rem / FRAMES_PER_MIN) + 1;
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const remInMin = rem % FRAMES_PER_MIN;
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// Shift by DROP so the label starts at :00;04 instead of :00;00
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const adj = remInMin + DROP;
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ss = Math.floor(adj / NOM);
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ff = adj % NOM;
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}
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const M = tm * 10 + m;
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return `${pad2(h)}:${pad2(M)}:${pad2(ss)};${pad2(ff)}`;
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}
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/**
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* Convert a 59.94 DF timecode string (HH:MM:SS;FF or HH:MM:SS:FF) to frame count.
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*/
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function tcToFrames(tc) {
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if (!tc) return 0;
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const clean = String(tc).replace(';', ':');
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const parts = clean.split(':').map(Number);
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if (parts.length !== 4) return 0;
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const [h, m, s, f] = parts;
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const totalMinutes = h * 60 + m;
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return (NOM * 3600 * h)
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+ (NOM * 60 * m)
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+ (NOM * s)
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+ f
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- DROP * (totalMinutes - Math.floor(totalMinutes / 10));
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}
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/**
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* Convert seconds (float) → frame count at 59.94.
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*/
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function secondsToFrames(seconds) {
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return Math.round(seconds * FPS_EXACT);
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}
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/**
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* Convert frame count → seconds (float) at 59.94.
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*/
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function framesToSeconds(frames) {
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return frames / FPS_EXACT;
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}
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global.TC = {
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framesToTC,
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tcToFrames,
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secondsToFrames,
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framesToSeconds,
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FPS: FPS_EXACT,
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};
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})(window);
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