fix(merge): fix progress formula for long videos, add optional totalDurationSec param, normalize Windows paths

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/main.ts

@@ -2428,6 +2428,29 @@ async function mergeVideos(
         return false;
     }
 
+    // Determine total duration for accurate progress
+    let mergeTotalDurationUs = 0;
+    if (totalDurationSec && totalDurationSec > 0) {
+        mergeTotalDurationUs = totalDurationSec * 1_000_000;
+    } else {
+        // Fallback: use ffprobe to get total duration of all input files
+        const ffprobe = getFFprobePath();
+        for (const filePath of inputFiles) {
+            try {
+                const result = execSync(
+                    `"${ffprobe}" -v quiet -show_entries format=duration -of csv=p=0 "${filePath}"`,
+                    { timeout: 10000, windowsHide: true }
+                ).toString().trim();
+                const dur = parseFloat(result);
+                if (!isNaN(dur)) {
+                    mergeTotalDurationUs += dur * 1_000_000;
+                }
+            } catch {
+                // If ffprobe fails, fall back to old behavior
+            }
+        }
+    }
+
     const runMergeAttempt = async (copyMode: boolean): Promise<boolean> => {
         const args = [
             '-f', 'concat',
@@ -2460,7 +2483,11 @@ async function mergeVideos(
                 const match = line.match(/out_time_us=(\d+)/);
                 if (match) {
                     const currentUs = parseInt(match[1], 10);
-                    onProgress(Math.min(99, currentUs / 10000000));
+                    if (mergeTotalDurationUs > 0) {
+                        onProgress(Math.min(99, (currentUs / mergeTotalDurationUs) * 100));
+                    } else {
+                        onProgress(Math.min(99, currentUs / 10000000));
+                    }
                 }
             });