fix(rendering): synchronize FPS, implement render locks, respect brand segment duration, and fix local audio path resolving for ffmpeg

src/engine/renderer/videoEncoder.ts

@@ -8,6 +8,12 @@ import { spawn } from 'child_process';
 import path from 'path';
 import fs from 'fs';
 
+export interface AudioTrackInput {
+  url: string;
+  startFrame: number;
+  volume: number; // 0 to 1
+}
+
 export interface EncodeOptions {
   /** Directory containing numbered frame images */
   framesDir: string;
@@ -25,6 +31,10 @@ export interface EncodeOptions {
   height?: number;
   /** Quality: CRF value (lower = better, 18-28 typical) */
   crf?: number;
+  /** Audio tracks to mix */
+  audioTracks?: AudioTrackInput[];
+  /** Total frames (used to force exact video length) */
+  durationInFrames?: number;
   /** Progress callback */
   onProgress?: (percent: number) => void;
 }
@@ -40,6 +50,8 @@ export async function encodeVideo(options: EncodeOptions): Promise<void> {
     fps,
     codec,
     crf = 23,
+    audioTracks = [],
+    durationInFrames,
     onProgress,
   } = options;
 
@@ -56,9 +68,14 @@ export async function encodeVideo(options: EncodeOptions): Promise<void> {
   const args: string[] = [
     '-y',                          // Overwrite output
     '-framerate', String(fps),     // Input framerate
-    '-i', inputPattern,            // Input pattern
+    '-i', inputPattern,            // Input 0: Image pattern
   ];
 
+  // Add audio inputs
+  audioTracks.forEach(track => {
+    args.push('-i', track.url);
+  });
+
   // Codec-specific settings
   if (codec === 'h264') {
     args.push(
@@ -84,6 +101,38 @@ export async function encodeVideo(options: EncodeOptions): Promise<void> {
     );
   }
 
+  // Audio codec
+  args.push('-c:a', 'aac', '-b:a', '192k');
+
+  // Build Audio Filter Complex
+  if (audioTracks.length > 0) {
+    const filterParts: string[] = [];
+    const mixInputs: string[] = [];
+
+    audioTracks.forEach((track, index) => {
+      const inputIndex = index + 1; // 0 is video
+      const delayMs = Math.round((track.startFrame / fps) * 1000);
+      const outLabel = `[a${inputIndex}]`;
+      
+      // adelay applies delay to all channels (L|R)
+      filterParts.push(`[${inputIndex}:a]adelay=${delayMs}|${delayMs},volume=${track.volume}${outLabel}`);
+      mixInputs.push(outLabel);
+    });
+
+    // Mix all processed audio streams
+    const mixFilter = `${mixInputs.join('')}amix=inputs=${audioTracks.length}:duration=longest:dropout_transition=2[aout]`;
+    filterParts.push(mixFilter);
+
+    args.push('-filter_complex', filterParts.join(';'));
+    args.push('-map', '0:v');       // Map video from input 0
+    args.push('-map', '[aout]');    // Map audio from complex filter
+  }
+
+  // Force video length
+  if (durationInFrames) {
+    args.push('-frames:v', String(Math.round(durationInFrames)));
+  }
+
   args.push(outputPath);
 
   // Count total frames for progress