diff --git a/public/index.html b/public/index.html
index db4ec5b..8c258b7 100644
--- a/public/index.html
+++ b/public/index.html
@@ -62,7 +62,7 @@
                     <div id="transcoding-overlay" class="player-overlay hidden">
                         <div class="spinner"></div>
                         <h3>Transcoding via FFmpeg...</h3>
-                        <p>Generating HLS segments, please wait.</p>
+                        <p>Generating MP4 file, please wait.</p>
                         <div id="progress-info" class="progress-info hidden">
                             <div id="progress-text" class="progress-text">Initializing...</div>
                             <div class="progress-bar">
diff --git a/public/js/main.js b/public/js/main.js
index fcff542..599432e 100644
--- a/public/js/main.js
+++ b/public/js/main.js
@@ -41,7 +41,7 @@ document.addEventListener('DOMContentLoaded', () => {
             }
             if (message.type === 'ready' && message.key === currentVideoKey) {
                 setProgress({ status: 'Ready to play', percent: 100, details: 'Ready to play' });
-                playHlsStream(message.hlsUrl);
+                playMp4Stream(message.mp4Url);
             }
         } catch (error) {
             console.error('WebSocket message parse error:', error);
@@ -246,7 +246,7 @@ document.addEventListener('DOMContentLoaded', () => {
             if (data.error) throw new Error(data.error);
 
             if (!wsConnected) {
-                pollForHlsReady(key, data.mp4Url);
+                pollForMp4Ready(key, data.mp4Url);
             }
         } catch (err) {
             console.error(err);
@@ -255,7 +255,7 @@ document.addEventListener('DOMContentLoaded', () => {
     };
 
     // Poll the backend to check if the generated MP4 file is accessible
-    const pollForHlsReady = (key, hlsUrl) => {
+    const pollForMp4Ready = (key, mp4Url) => {
         let attempts = 0;
         const maxAttempts = 120; // 60 seconds max wait for first segment
         const pollIntervalMs = 500;
@@ -273,10 +273,10 @@ document.addEventListener('DOMContentLoaded', () => {
                 if (data.ready) {
                     stopPolling();
                     setProgress({ status: 'Ready to play', percent: 100, details: 'Ready to play' });
-                    playHlsStream(data.hlsUrl);
+                    playMp4Stream(data.mp4Url);
                 } else if (attempts >= maxAttempts) {
                     stopPolling();
-                    transcodingOverlay.innerHTML = `<p style="color: #ef4444;">Timeout waiting for HLS segments.</p>`;
+                    transcodingOverlay.innerHTML = `<p style="color: #ef4444;">Timeout waiting for MP4 file.</p>`;
                 }
             } catch (err) {
                 console.error("Poll Error:", err);
@@ -292,7 +292,7 @@ document.addEventListener('DOMContentLoaded', () => {
     };
 
     // Initialize MP4 Player
-    const playHlsStream = (url) => {
+    const playMp4Stream = (url) => {
         transcodingOverlay.classList.add('hidden');
         videoPlayer.classList.remove('hidden');
         playBtn.classList.add('hidden');
diff --git a/server.js b/server.js
index 95baf27..139e1a8 100644
--- a/server.js
+++ b/server.js
@@ -200,12 +200,27 @@ app.post('/api/transcode', async (req, res) => {
                 progressMap[progressKey] = progressState;
                 broadcastWs(progressKey, { type: 'progress', key: progressKey, progress: progressState });
             })
+            .on('stderr', (stderrLine) => {
+                console.log(`ffmpeg stderr: ${stderrLine}`);
+            })
             .on('end', () => {
                 console.log(`Finished transcoding ${key} to MP4`);
-                const progressState = { status: 'finished', percent: 100, details: 'Transcoding complete', mp4Url };
+                let progressState;
+                try {
+                    const stats = fs.statSync(mp4Path);
+                    if (!stats.isFile() || stats.size === 0) {
+                        throw new Error('Output MP4 is empty or missing');
+                    }
+                    progressState = { status: 'finished', percent: 100, details: 'Transcoding complete', mp4Url };
+                } catch (verifyError) {
+                    console.error(`Output verification failed for ${mp4Path}:`, verifyError);
+                    progressState = { status: 'failed', percent: progressMap[progressKey]?.percent || 0, details: `Output verification failed: ${verifyError.message}`, mp4Url };
+                }
                 progressMap[progressKey] = progressState;
                 broadcastWs(progressKey, { type: 'progress', key: progressKey, progress: progressState });
-                broadcastWs(progressKey, { type: 'ready', key: progressKey, mp4Url });
+                if (progressState.status === 'finished') {
+                    broadcastWs(progressKey, { type: 'ready', key: progressKey, mp4Url });
+                }
             })
             .on('error', (err) => {
                 console.error(`Error transcoding ${key}:`, err);
@@ -234,8 +249,8 @@ app.get('/api/status', (req, res) => {
     const mp4Path = path.join(__dirname, 'public', 'mp4', ...safeKeySegments, 'video.mp4');
     const progress = progressMap[progressKey] || null;
 
-    // Check if the MP4 file exists
-    if (fs.existsSync(mp4Path)) {
+    const outputReady = fs.existsSync(mp4Path) && (!progress || progress.status !== 'failed');
+    if (outputReady) {
         res.json({ ready: true, mp4Url: `/mp4/${safeKeySegments.join('/')}/video.mp4`, progress });
     } else {
         res.json({ ready: false, progress });