fix: address CodeRabbit review — muxing error guard, dead code removal, i18n

- Add encoderError check after awaiting pendingMuxing to prevent
  finalization of corrupt exports (both exporters)
- Remove unreachable synchronous fast-path in getMediaDurationSec
- Set preload='metadata' before src for correct browser behavior
- Localize audio processing status text with t()

src/components/video-editor/VideoEditor.tsx

@@ -4454,7 +4454,7 @@ export default function VideoEditor() {
 									</p>
 									{isRenderingAudio ? (
 										<p className="mt-1 text-[11px] text-muted-foreground/70">
-											Processing audio with speed/overlay edits
+											{t("editor.export.processingAudioEdits", "Processing audio with speed/overlay edits")}
 										</p>
 									) : exportRenderSpeedLabel ? (
 										<p className="mt-1 text-[11px] text-muted-foreground/70">

src/lib/exporter/audioEncoder.ts

@@ -1149,17 +1149,8 @@ export class AudioProcessor {
 		const source = await resolveMediaElementSource(url);
 		try {
 			const media = document.createElement("video");
-			media.src = source.src;
 			media.preload = "metadata";
-
-			if (
-				Number.isFinite(media.duration) &&
-				media.readyState >= HTMLMediaElement.HAVE_METADATA
-			) {
-				const duration = media.duration;
-				media.src = "";
-				return duration;
-			}
+			media.src = source.src;
 
 			return await new Promise<number>((resolve, reject) => {
 				const timeout = setTimeout(() => {

src/lib/exporter/modernVideoExporter.ts

@@ -434,6 +434,11 @@ export class ModernVideoExporter {
 				"muxing queued video chunks",
 			);
 
+			// Surface muxing errors before proceeding with finalization
+			if (this.encoderError) {
+				throw this.encoderError;
+			}
+
 			if (nativeAudioPlan.audioMode !== "none" && !shouldUseFfmpegAudioFallback && !this.cancelled) {
 				const demuxer = this.streamingDecoder.getDemuxer();
 				if (
@@ -1399,8 +1404,9 @@ export class ModernVideoExporter {
 						}
 					} catch (error) {
 						console.error("Muxing error:", error);
+						const muxingError = error instanceof Error ? error : new Error(String(error));
 						if (!this.encoderError) {
-							this.encoderError = error instanceof Error ? error : new Error(String(error));
+							this.encoderError = muxingError;
 						}
 						this.cancelled = true;
 					}

src/lib/exporter/videoExporter.ts

@@ -293,6 +293,11 @@ export class VideoExporter {
 				"muxing queued video chunks",
 			);
 
+			// Surface muxing errors before proceeding with finalization
+			if (this.encoderError) {
+				throw this.encoderError;
+			}
+
 			if (hasAudio && !shouldUseFfmpegAudioFallback && !this.cancelled) {
 				const demuxer = this.streamingDecoder.getDemuxer();
 				if (demuxer || hasAudioRegions || hasSourceAudioFallback) {
@@ -979,6 +984,11 @@ export class VideoExporter {
 						}
 					} catch (error) {
 						console.error("Muxing error:", error);
+						const muxingError = error instanceof Error ? error : new Error(String(error));
+						if (!this.encoderError) {
+							this.encoderError = muxingError;
+						}
+						this.cancelled = true;
 					}
 				});
 				this.encodeQueue--;