diff --git a/server.js b/server.js
index a4ef5d0..b55dbd2 100644
--- a/server.js
+++ b/server.js
@@ -142,6 +142,7 @@ const createS3Client = (credentials) => {
 const progressMap = {};
 const transcodeProcesses = new Map();
 const wsSubscriptions = new Map();
+const activeDownloads = new Map();
 
 const AVAILABLE_VIDEO_ENCODERS = [
     { value: 'h264_rkmpp', label: 'H.264(RKMPP HighSpeed)' },
@@ -386,6 +387,107 @@ wss.on('connection', (ws) => {
     ws.on('close', () => removeWsClient(ws));
 });
 
+const ensureS3Downloaded = async (s3Client, bucket, key, tmpInputPath, progressKey, streamSessionId) => {
+    if (activeDownloads.has(progressKey)) {
+        try {
+            await activeDownloads.get(progressKey);
+        } catch (err) {
+            // Ignore error and retry if previous failed
+        }
+    }
+
+    if (fs.existsSync(tmpInputPath)) {
+        const stats = fs.statSync(tmpInputPath);
+        const totalBytes = stats.size;
+        progressMap[progressKey] = {
+            status: 'downloaded',
+            percent: 100,
+            downloadedBytes: totalBytes,
+            totalBytes,
+            streamSessionId,
+            details: 'Source already downloaded locally...',
+            mp4Url: null
+        };
+        broadcastWs(progressKey, { type: 'progress', key, progress: progressMap[progressKey] });
+        return;
+    }
+
+    const downloadPromise = (async () => {
+        const command = new GetObjectCommand({ Bucket: bucket, Key: key });
+        const response = await s3Client.send(command);
+        const totalBytes = response.ContentLength || 0;
+        const s3Stream = response.Body;
+        let downloadedBytes = 0;
+
+        const downloadingPath = tmpInputPath + '.downloading';
+
+        progressMap[progressKey] = {
+            status: 'downloading',
+            percent: 0,
+            downloadedBytes: 0,
+            totalBytes,
+            streamSessionId,
+            details: 'Downloading full source...',
+            mp4Url: null
+        };
+        broadcastWs(progressKey, { type: 'progress', key, progress: progressMap[progressKey] });
+
+        await new Promise((resolve, reject) => {
+            const writeStream = fs.createWriteStream(downloadingPath);
+
+            s3Stream.on('data', (chunk) => {
+                downloadedBytes += chunk.length;
+                const percent = totalBytes ? Math.min(100, Math.round((downloadedBytes / totalBytes) * 100)) : 0;
+                const downloadState = {
+                    status: 'downloading',
+                    percent,
+                    downloadedBytes,
+                    totalBytes,
+                    streamSessionId,
+                    details: totalBytes ? `Downloading source ${percent}%` : 'Downloading source...',
+                    mp4Url: null
+                };
+                progressMap[progressKey] = downloadState;
+                broadcastWs(progressKey, { type: 'progress', key, progress: downloadState });
+            });
+
+            s3Stream.on('error', reject);
+            writeStream.on('error', reject);
+            writeStream.on('finish', () => {
+                try {
+                    fs.renameSync(downloadingPath, tmpInputPath);
+                    resolve();
+                } catch (e) {
+                    reject(e);
+                }
+            });
+            s3Stream.pipe(writeStream);
+        });
+
+        progressMap[progressKey] = {
+            status: 'downloaded',
+            percent: 100,
+            downloadedBytes,
+            totalBytes,
+            streamSessionId,
+            details: 'Source download complete...',
+            mp4Url: null
+        };
+        broadcastWs(progressKey, { type: 'progress', key, progress: progressMap[progressKey] });
+    })();
+
+    activeDownloads.set(progressKey, downloadPromise);
+    try {
+        await downloadPromise;
+    } catch (err) {
+        if (fs.existsSync(tmpInputPath + '.downloading')) {
+            fs.rmSync(tmpInputPath + '.downloading', { force: true });
+        }
+        throw err;
+    } finally {
+        activeDownloads.delete(progressKey);
+    }
+};
 
 const clearDownloadCache = () => {
     const tmpDir = CACHE_DIR;
@@ -575,84 +677,14 @@ app.get('/api/hls/playlist.m3u8', async (req, res) => {
 
     const auth = await extractS3Credentials(req);
     const s3Client = createS3Client(auth);
-    let totalBytes = 0;
     const progressKey = getProgressKey(key);
     const streamSessionId = createStreamSessionId();
-    let downloadedBytes = 0;
 
-    if (!fs.existsSync(tmpInputPath)) {
-        try {
-            const command = new GetObjectCommand({ Bucket: bucket, Key: key });
-            const response = await s3Client.send(command);
-            totalBytes = response.ContentLength;
-            const s3Stream = response.Body;
-
-            progressMap[progressKey] = {
-                status: 'downloading',
-                percent: 0,
-                downloadedBytes: 0,
-                totalBytes,
-                streamSessionId,
-                details: 'Downloading full source before streaming...',
-                mp4Url: null
-            };
-            broadcastWs(progressKey, { type: 'progress', key, progress: progressMap[progressKey] });
-
-            await new Promise((resolve, reject) => {
-                const writeStream = fs.createWriteStream(tmpInputPath);
-
-                s3Stream.on('data', (chunk) => {
-                    downloadedBytes += chunk.length;
-                    const percent = totalBytes ? Math.min(100, Math.round((downloadedBytes / totalBytes) * 100)) : 0;
-
-                    const downloadState = {
-                        status: 'downloading',
-                        percent,
-                        downloadedBytes,
-                        totalBytes,
-                        streamSessionId,
-                        details: totalBytes ? `Downloading source ${percent}%` : 'Downloading source...',
-                        mp4Url: null
-                    };
-                    progressMap[progressKey] = downloadState;
-                    broadcastWs(progressKey, { type: 'progress', key, progress: downloadState });
-                });
-
-                s3Stream.on('error', reject);
-                writeStream.on('error', reject);
-                writeStream.on('finish', resolve);
-                s3Stream.pipe(writeStream);
-            });
-
-            progressMap[progressKey] = {
-                status: 'downloaded',
-                percent: 100,
-                downloadedBytes,
-                totalBytes,
-                streamSessionId,
-                details: 'Source download complete, parsing for HLS...',
-                mp4Url: null
-            };
-            broadcastWs(progressKey, { type: 'progress', key, progress: progressMap[progressKey] });
-
-        } catch (err) {
-            console.error('S3 Download Failed:', err);
-            return res.status(500).send('S3 Download Failed');
-        }
-    } else {
-        const stats = fs.statSync(tmpInputPath);
-        totalBytes = stats.size;
-        downloadedBytes = totalBytes;
-        progressMap[progressKey] = {
-            status: 'downloaded',
-            percent: 100,
-            downloadedBytes,
-            totalBytes,
-            streamSessionId,
-            details: 'Source already downloaded locally, parsing for HLS...',
-            mp4Url: null
-        };
-        broadcastWs(progressKey, { type: 'progress', key, progress: progressMap[progressKey] });
+    try {
+        await ensureS3Downloaded(s3Client, bucket, key, tmpInputPath, progressKey, streamSessionId);
+    } catch (err) {
+        console.error('S3 Download Failed:', err);
+        return res.status(500).send('S3 Download Failed');
     }
 
     let duration = 0;
@@ -881,74 +913,7 @@ app.get('/api/stream', async (req, res) => {
             broadcastWs(progressKey, { type: 'progress', key, progress: progressMap[progressKey] });
         }
 
-        let totalBytes = 0;
-        let downloadedBytes = 0;
-
-        if (!cacheExists) {
-            const command = new GetObjectCommand({ Bucket: bucket, Key: key });
-            const response = await s3Client.send(command);
-            const s3Stream = response.Body;
-            totalBytes = response.ContentLength || 0;
-
-            progressMap[progressKey] = {
-                status: 'downloading',
-                percent: 0,
-                downloadedBytes: 0,
-                totalBytes,
-                streamSessionId,
-                details: 'Downloading full source before streaming...',
-                mp4Url: null
-            };
-            broadcastWs(progressKey, { type: 'progress', key, progress: progressMap[progressKey] });
-
-            await new Promise((resolve, reject) => {
-                const writeStream = fs.createWriteStream(tmpInputPath);
-                s3Stream.on('data', (chunk) => {
-                    downloadedBytes += chunk.length;
-                    const percent = totalBytes ? Math.min(100, Math.round(downloadedBytes / totalBytes * 100)) : 0;
-                    const downloadState = {
-                        status: 'downloading',
-                        percent,
-                        downloadedBytes,
-                        totalBytes,
-                        streamSessionId,
-                        details: totalBytes ? `Downloading source ${percent}%` : 'Downloading source...',
-                        mp4Url: null
-                    };
-                    progressMap[progressKey] = downloadState;
-                    broadcastWs(progressKey, { type: 'progress', key, progress: downloadState });
-                });
-                s3Stream.on('error', reject);
-                writeStream.on('error', reject);
-                writeStream.on('finish', resolve);
-                s3Stream.pipe(writeStream);
-            });
-
-            progressMap[progressKey] = {
-                status: 'downloaded',
-                percent: 100,
-                downloadedBytes,
-                totalBytes,
-                streamSessionId,
-                details: 'Source download complete, starting real-time transcode...',
-                mp4Url: null
-            };
-            broadcastWs(progressKey, { type: 'progress', key, progress: progressMap[progressKey] });
-        } else {
-            const stats = fs.statSync(tmpInputPath);
-            totalBytes = stats.size;
-            downloadedBytes = totalBytes;
-            progressMap[progressKey] = {
-                status: 'downloaded',
-                percent: 100,
-                downloadedBytes,
-                totalBytes,
-                streamSessionId,
-                details: 'Source already downloaded locally, starting real-time transcode...',
-                mp4Url: null
-            };
-            broadcastWs(progressKey, { type: 'progress', key, progress: progressMap[progressKey] });
-        }
+        await ensureS3Downloaded(s3Client, bucket, key, tmpInputPath, progressKey, streamSessionId);
 
         // Probe file for duration and broadcast to clients
         let sourceMetadata = null;