Improve playback of videos in Tracking Details (#22301)

* prevent short hls segments by extending clip backwards

* clean up

* snap to keyframe instead of arbitrarily subtracting time

* formatting

frigate/api/media.py

@@ -50,10 +50,12 @@ from frigate.models import Event, Previews, Recordings, Regions, ReviewSegment
 from frigate.track.object_processing import TrackedObjectProcessor
 from frigate.util.file import get_event_thumbnail_bytes
 from frigate.util.image import get_image_from_recording
+from frigate.util.media import get_keyframe_before
 from frigate.util.time import get_dst_transitions
 
 logger = logging.getLogger(__name__)
 
+
 router = APIRouter(tags=[Tags.media])
 
 
@@ -900,6 +902,33 @@ async def vod_ts(
         if recording.end_time > end_ts:
             duration -= int((recording.end_time - end_ts) * 1000)
 
+        # nginx-vod-module pushes clipFrom forward to the next keyframe,
+        # which can leave too few frames and produce an empty/unplayable
+        # segment. Snap clipFrom back to the preceding keyframe so the
+        # segment always starts with a decodable frame.
+        if "clipFrom" in clip:
+            keyframe_ms = get_keyframe_before(recording.path, clip["clipFrom"])
+            if keyframe_ms is not None:
+                gained = clip["clipFrom"] - keyframe_ms
+                clip["clipFrom"] = keyframe_ms
+                duration += gained
+                logger.debug(
+                    "VOD: snapped clipFrom to keyframe at %sms for %s, duration now %sms",
+                    keyframe_ms,
+                    recording.path,
+                    duration,
+                )
+            else:
+                # could not read keyframes, remove clipFrom to use full recording
+                logger.debug(
+                    "VOD: no keyframe info for %s, removing clipFrom to use full recording",
+                    recording.path,
+                )
+                del clip["clipFrom"]
+                duration = int(recording.duration * 1000)
+                if recording.end_time > end_ts:
+                    duration -= int((recording.end_time - end_ts) * 1000)
+
         if duration < min_duration_ms:
             # skip if the clip has no valid duration (too short to contain frames)
             logger.debug(