diff --git a/server.js b/server.js
index 2894228..8da0056 100644
--- a/server.js
+++ b/server.js
@@ -92,6 +92,17 @@ const progressMap = {};
 const transcodeProcesses = new Map();
 const wsSubscriptions = new Map();
 const progressApiLogMap = new Map();
+const progressStateLogMap = new Map();
+
+const setProgressState = (progressKey, key, nextState, reason = '') => {
+    progressMap[progressKey] = nextState;
+    const signature = `${nextState?.status || 'null'}:${typeof nextState?.percent === 'number' ? nextState.percent : 'na'}:${nextState?.streamSessionId || 'na'}`;
+    if (progressStateLogMap.get(progressKey) !== signature) {
+        progressStateLogMap.set(progressKey, signature);
+        console.log(`[progress-state] key=${key} status=${nextState?.status || 'null'} percent=${typeof nextState?.percent === 'number' ? nextState.percent : 'na'} reason=${reason || 'unspecified'} session=${nextState?.streamSessionId || 'na'}`);
+    }
+    return nextState;
+};
 
 const AVAILABLE_VIDEO_ENCODERS = [
     { value: 'h264_rkmpp', label: 'h264_rkmpp (RKMPP H.264)' },
@@ -800,12 +811,12 @@ app.post('/api/stop-transcode', (req, res) => {
             return res.status(404).json({ error: 'No active transcode found for this key' });
         }
         stopActiveTranscode(progressKey);
-        progressMap[progressKey] = {
+        setProgressState(progressKey, key, {
             status: 'cancelled',
             percent: 0,
             details: 'Transcode stopped by user',
             mp4Url: null
-        };
+        }, 'stop-transcode');
         broadcastWs(progressKey, { type: 'progress', key, progress: progressMap[progressKey] });
         res.json({ message: 'Transcode stopped' });
     } catch (error) {
@@ -868,7 +879,7 @@ app.get('/api/stream', async (req, res) => {
     try {
         const replacedExistingStream = stopActiveTranscode(progressKey);
         if (replacedExistingStream && startSeconds > 0) {
-            progressMap[progressKey] = {
+            setProgressState(progressKey, key, {
                 ...(progressMap[progressKey] || {}),
                 status: 'transcoding',
                 percent: Math.min(Math.max(Math.round((startSeconds / Math.max(progressMap[progressKey]?.duration || startSeconds || 1, 1)) * 100), 0), 100),
@@ -876,7 +887,7 @@ app.get('/api/stream', async (req, res) => {
                 streamSessionId,
                 details: `Restarting transcode from ${startSeconds.toFixed(2)}s`,
                 mp4Url: null
-            };
+            }, 'restart-seek');
             broadcastWs(progressKey, { type: 'progress', key, progress: progressMap[progressKey] });
         }
 
@@ -885,7 +896,7 @@ app.get('/api/stream', async (req, res) => {
         const cacheExists = fs.existsSync(downloadPath);
 
         if (!cacheExists) {
-            progressMap[progressKey] = {
+            setProgressState(progressKey, key, {
                 status: 'downloading',
                 percent: 0,
                 downloadedBytes: 0,
@@ -893,7 +904,7 @@ app.get('/api/stream', async (req, res) => {
                 streamSessionId,
                 details: 'Downloading full source before streaming...',
                 mp4Url: null
-            };
+            }, 'download-start');
             broadcastWs(progressKey, { type: 'progress', key, progress: progressMap[progressKey] });
 
             await ensureSourceCached({
@@ -915,12 +926,12 @@ app.get('/api/stream', async (req, res) => {
                         details: totalBytes ? `Downloading source ${percent}%` : 'Downloading source...',
                         mp4Url: null
                     };
-                    progressMap[progressKey] = downloadState;
+                    setProgressState(progressKey, key, downloadState, 'download-progress');
                     broadcastWs(progressKey, { type: 'progress', key, progress: downloadState });
                 }
             });
 
-            progressMap[progressKey] = {
+            setProgressState(progressKey, key, {
                 status: 'downloaded',
                 percent: 100,
                 downloadedBytes,
@@ -928,14 +939,14 @@ app.get('/api/stream', async (req, res) => {
                 streamSessionId,
                 details: 'Source download complete, starting real-time transcode...',
                 mp4Url: null
-            };
+            }, 'download-complete');
             broadcastWs(progressKey, { type: 'progress', key, progress: progressMap[progressKey] });
         } else {
             const stats = fs.statSync(downloadPath);
             totalBytes = stats.size;
             downloadedBytes = totalBytes;
             console.log(`[download] cache ready bucket=${bucket} key=${key} path=${downloadPath} bytes=${totalBytes}`);
-            progressMap[progressKey] = {
+            setProgressState(progressKey, key, {
                 status: 'downloaded',
                 percent: 100,
                 downloadedBytes,
@@ -943,7 +954,7 @@ app.get('/api/stream', async (req, res) => {
                 streamSessionId,
                 details: 'Source already downloaded locally, starting real-time transcode...',
                 mp4Url: null
-            };
+            }, 'download-cache-hit');
             broadcastWs(progressKey, { type: 'progress', key, progress: progressMap[progressKey] });
         }
 
@@ -953,11 +964,11 @@ app.get('/api/stream', async (req, res) => {
             const metadata = await probeFile(downloadPath);
             sourceMetadata = metadata;
             const duration = metadata.format?.duration || 0;
-            progressMap[progressKey] = {
+            setProgressState(progressKey, key, {
                 ...(progressMap[progressKey] || {}),
                 duration: parseFloat(duration) || 0,
                 streamSessionId
-            };
+            }, 'duration-probed');
             broadcastWs(progressKey, { type: 'duration', key, duration: parseFloat(duration) });
         } catch (probeErr) {
             console.error('Probe failed:', probeErr);
@@ -1049,7 +1060,7 @@ app.get('/api/stream', async (req, res) => {
                         details: `Streaming transcode ${percent}%`,
                         mp4Url: null
                     };
-                    progressMap[progressKey] = progressState;
+                    setProgressState(progressKey, key, progressState, 'transcode-progress');
                     broadcastWs(progressKey, { type: 'progress', key, progress: progressState });
                 })
                 .on('stderr', (stderrLine) => {
@@ -1064,7 +1075,7 @@ app.get('/api/stream', async (req, res) => {
                     }
                     console.log(`[transcode] complete bucket=${bucket} key=${key} encoder=${encoderName} cache=${convertPath}`);
                     transcodeProcesses.delete(progressKey);
-                    progressMap[progressKey] = {
+                    setProgressState(progressKey, key, {
                         status: 'finished',
                         percent: 100,
                         duration: progressMap[progressKey]?.duration || null,
@@ -1072,7 +1083,7 @@ app.get('/api/stream', async (req, res) => {
                         streamSessionId,
                         details: 'Streaming transcode complete',
                         mp4Url: null
-                    };
+                    }, 'transcode-finished');
                     broadcastWs(progressKey, { type: 'progress', key, progress: progressMap[progressKey] });
                 })
                 .on('error', (err) => {
@@ -1090,7 +1101,7 @@ app.get('/api/stream', async (req, res) => {
                         details: err.message || 'Streaming transcode failed',
                         mp4Url: null
                     };
-                    progressMap[progressKey] = failedState;
+                    setProgressState(progressKey, key, failedState, 'transcode-failed');
                     broadcastWs(progressKey, { type: 'progress', key, progress: failedState });
                     if (!res.headersSent) {
                         res.status(500).json({ error: 'Failed to stream transcoded video', detail: err.message });