Fix MP4 mux for web playback: add faststart and genpts

- Add -movflags +faststart to move moov atom to start
- Add -fflags +genpts for proper timestamp generation
- Fixes jerky playback and video/audio desync

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

app/routers/runs.py

@@ -402,25 +402,31 @@ async def get_run(
             # Detect media type using magic bytes, fall back to database item_type
             output_cid = run["output_cid"]
             media_type = None
-            try:
-                from ..services.run_service import detect_media_type
-                cache_path = get_cache_manager().get_by_cid(output_cid)
-                if cache_path and cache_path.exists():
-                    simple_type = detect_media_type(cache_path)
-                    media_type = type_to_mime(simple_type)
-                    output_media_type = media_type
-            except Exception:
-                pass
-            # Fall back to database item_type if local detection failed
-            if not media_type:
+
+            # Streaming runs (with ipfs_cid) are always video/mp4
+            if run.get("ipfs_cid"):
+                media_type = "video/mp4"
+                output_media_type = media_type
+            else:
                 try:
-                    import database
-                    item_types = await database.get_item_types(output_cid, run.get("actor_id"))
-                    if item_types:
-                        media_type = type_to_mime(item_types[0].get("type"))
+                    from ..services.run_service import detect_media_type
+                    cache_path = get_cache_manager().get_by_cid(output_cid)
+                    if cache_path and cache_path.exists():
+                        simple_type = detect_media_type(cache_path)
+                        media_type = type_to_mime(simple_type)
                         output_media_type = media_type
                 except Exception:
                     pass
+                # Fall back to database item_type if local detection failed
+                if not media_type:
+                    try:
+                        import database
+                        item_types = await database.get_item_types(output_cid, run.get("actor_id"))
+                        if item_types:
+                            media_type = type_to_mime(item_types[0].get("type"))
+                            output_media_type = media_type
+                    except Exception:
+                        pass
             artifacts.append({
                 "cid": output_cid,
                 "step_name": "Output",
@@ -568,13 +574,17 @@ async def list_runs(
     for run in runs:
         # Add output media info
         if run.get("output_cid"):
-            try:
-                cache_path = cache_manager.get_by_cid(run["output_cid"])
-                if cache_path and cache_path.exists():
-                    simple_type = detect_media_type(cache_path)
-                    run["output_media_type"] = type_to_mime(simple_type)
-            except Exception:
-                pass
+            # Streaming runs (with ipfs_cid) are always video/mp4
+            if run.get("ipfs_cid"):
+                run["output_media_type"] = "video/mp4"
+            else:
+                try:
+                    cache_path = cache_manager.get_by_cid(run["output_cid"])
+                    if cache_path and cache_path.exists():
+                        simple_type = detect_media_type(cache_path)
+                        run["output_media_type"] = type_to_mime(simple_type)
+                except Exception:
+                    pass
 
         # Add input media info (first 3 inputs)
         input_previews = []

app/templates/runs/detail.html

@@ -575,7 +575,7 @@
         {# Inline media preview - prefer IPFS URLs when available #}
         <div class="mb-4">
             {% if output_media_type and output_media_type.startswith('image/') %}
-            <a href="/cache/{{ run.output_cid }}" class="block">
+            <a href="{% if run.ipfs_cid %}/ipfs/{{ run.ipfs_cid }}{% else %}/cache/{{ run.output_cid }}{% endif %}" class="block">
                 <img src="{% if run.ipfs_cid %}/ipfs/{{ run.ipfs_cid }}{% else %}/cache/{{ run.output_cid }}/raw{% endif %}" alt="Output"
                      class="max-w-full max-h-96 rounded-lg mx-auto">
             </a>
@@ -593,14 +593,15 @@
         </div>
 
         <div class="flex items-center justify-between">
-            <a href="/cache/{{ run.output_cid }}" class="font-mono text-sm text-blue-400 hover:text-blue-300">
-                {{ run.output_cid }}
+            <a href="{% if run.ipfs_cid %}/ipfs/{{ run.ipfs_cid }}{% else %}/cache/{{ run.output_cid }}{% endif %}"
+               class="font-mono text-sm text-blue-400 hover:text-blue-300">
+                {% if run.ipfs_cid %}{{ run.ipfs_cid }}{% else %}{{ run.output_cid }}{% endif %}
             </a>
             {% if run.ipfs_cid %}
             <a href="https://ipfs.io/ipfs/{{ run.ipfs_cid }}"
                target="_blank"
                class="text-gray-400 hover:text-white text-sm">
-                IPFS: {{ run.ipfs_cid[:16] }}...
+                View on IPFS Gateway
             </a>
             {% endif %}
         </div>

tasks/streaming.py

@@ -411,6 +411,8 @@ def run_stream(
             "ffmpeg", "-y",
             "-i", str(hls_playlist),
             "-c", "copy",  # Just copy streams, no re-encoding
+            "-movflags", "+faststart",  # Move moov atom to start for web playback
+            "-fflags", "+genpts",  # Generate proper timestamps
             str(final_mp4)
         ]
         logger.info(f"Muxing HLS to MP4: {' '.join(mux_cmd)}")