bus_analyzer: use 0.1s before the end timestamp, not the exact end

to lower latency

bus_analyzer/bus_analyzer/extract.py

@@ -344,10 +344,10 @@ def recognize_time_of_day(frame):
 	return best, distance
 
 
-def extract_segment(prototypes, segment):
+def extract_segment(prototypes, segment, time):
 	ODO_SCORE_THRESHOLD = 0.01
 	CLOCK_SCORE_THRESHOLD = 0.01
-	frame_data = b"".join(extract_frame([segment], segment.start))
+	frame_data = b"".join(extract_frame([segment], time))
 	frame = Image.open(BytesIO(frame_data))
 	odometer, score, _ = recognize_odometer(prototypes, frame)
 	if score < ODO_SCORE_THRESHOLD:

bus_analyzer/bus_analyzer/main.py

@@ -26,7 +26,7 @@ def do_extract_segment(*segment_paths, prototypes_path="./prototypes"):
 	prototypes = load_prototypes(prototypes_path)
 	for segment_path in segment_paths:
 		segment_info = parse_segment_path(segment_path)
-		odometer, clock, tod = extract_segment(prototypes, segment_info)
+		odometer, clock, tod = extract_segment(prototypes, segment_info, segment_info.start)
 		print(f"{segment_path} {odometer} {clock} {tod}")
 
 
@@ -76,7 +76,7 @@ def compare_segments(dbconnect, base_dir='.', prototypes_path="./prototypes", si
 	for old_odometer, (segment, old_clock, old_tod) in selected:
 		path = os.path.join(base_dir, segment)
 		segment_info = parse_segment_path(path)
-		odometer, clock, tod = extract_segment(prototypes, segment_info)
+		odometer, clock, tod = extract_segment(prototypes, segment_info, segment_info.start)
 		results.append((segment, {
 			"odo": (old_odometer, odometer),
 			"clock": (old_clock, clock),
@@ -118,8 +118,13 @@ def analyze_segment(db_manager, prototypes, segment_path, check_segment_name=Non
 	if check_segment_name is not None:
 		assert segment_name == check_segment_name
 
+	# A timestamp fully at the end doesn't get us a valid frame.
+	# But we want to be as late as possible to minimize latency.
+	# We attempt to do a fixed time before the end, or use the start if too short.
+	timestamp = max(segment_info.start, segment_info.end - datetime.timedelta(seconds=0.1))
+
 	try:
-		odometer, clock, tod = extract_segment(prototypes, segment_info)
+		odometer, clock, tod = extract_segment(prototypes, segment_info, timestamp)
 	except Exception:
 		logging.warning(f"Failed to extract segment {segment_path!r}", exc_info=True)
 		odometer = None
@@ -143,7 +148,7 @@ def analyze_segment(db_manager, prototypes, segment_path, check_segment_name=Non
 					timeofday = %(timeofday)s
 		""",
 		channel=segment_info.channel,
-		timestamp=segment_info.start,
+		timestamp=timestamp,
 		segment=segment_name,
 		error=error,
 		odometer=odometer,
@@ -200,7 +205,7 @@ def main(
 	prototypes_path="./prototypes",
 	concurrency=10,
 ):
-	CHECK_INTERVAL = 2
+	CHECK_INTERVAL = 0.5
 
 	stopping = gevent.event.Event()