Timestamp capture

examples/timestamp_capture.py

@@ -0,0 +1,49 @@
+#!/usr/bin/python3
+
+import time
+
+from picamera2 import Picamera2
+
+
+def check_request_timestamp(request, check_time):
+    md = request.get_metadata()
+    # 'SensorTimestamp' is when the first pixel was read out, so it started being
+    # exposed 'ExposureTime' earlier.
+    exposure_start_time = md['SensorTimestamp'] - 1000 * md['ExposureTime']
+    if exposure_start_time < check_time:
+        print("ERROR: request captured too early by", check_time - exposure_start_time, "nanoseconds")
+
+
+picam2 = Picamera2()
+picam2.start()
+
+time.sleep(1)
+
+# Capture a request that is guaranteed not to have started being exposed before
+# we make the request. Do it 30 times as a test. Note that this kind of thing is
+# likely cut the apparent framerate because of all the stopping and waiting for sync.
+
+for _ in range(30):
+    check_time = time.monotonic_ns()
+    request = picam2.capture_request(flush=True)
+    check_request_timestamp(request, check_time)
+    request.release()
+
+# Capture a request where nothing started being exposed until 1/2s in the
+# future. Do this 10 times as a test.
+
+for _ in range(10):
+    check_time = time.monotonic_ns() + 5e8
+    request = picam2.capture_request(flush=check_time)
+    check_request_timestamp(request, check_time)
+    request.release()
+
+# Let's do this last test again, but using asynchronous operation.
+
+for _ in range(10):
+    check_time = time.monotonic_ns() + 5e8
+    job = picam2.capture_request(flush=check_time, wait=False)
+    # Now we can do other stuff while waiting for the capture.
+    request = picam2.wait(job)
+    check_request_timestamp(request, check_time)
+    request.release()

picamera2/picamera2.py

@@ -1309,12 +1309,24 @@ def set_frame_drops_(self, num_frames):
         return (True, None)
 
     def drop_frames_(self):
-        if not self.completed_requests:
-            return (False, None)
-        if self._frame_drops == 0:
+        while self.completed_requests:
+            if self._frame_drops == 0:
+                return (True, None)
+            self.completed_requests.pop(0).release()
+            self._frame_drops -= 1
+        return (False, None)
+
+    def wait_for_timestamp_(self, timestamp_ns):
+        # No wait requested. This function in the job is done.
+        if not timestamp_ns:
             return (True, None)
-        self.completed_requests.pop(0).release()
-        self._frame_drops -= 1
+        while self.completed_requests:
+            # Check if frame started being exposed after the timestamp.
+            md = self.completed_requests[0].get_metadata()
+            frame_timestamp_ns = md['SensorTimestamp'] - 1000 * md['ExposureTime']
+            if frame_timestamp_ns >= timestamp_ns:
+                return (True, None)
+            self.completed_requests.pop(0).release()
         return (False, None)
 
     def drop_frames(self, num_frames, wait=None, signal_function=None):
@@ -1413,13 +1425,17 @@ def capture_request_(self):
             return (False, None)
         return (True, self.completed_requests.pop(0))
 
-    def capture_request(self, wait=None, signal_function=None):
+    def capture_request(self, wait=None, signal_function=None, flush=None):
         """Fetch the next completed request from the camera system.
 
         You will be holding a reference to this request so you must release it again to return it
         to the camera system.
         """
-        functions = [self.capture_request_]
+        # flush will be the timestamp in ns that we wait for (if any)
+        if flush is True:
+            flush = time.monotonic_ns()
+        functions = [partial(self.wait_for_timestamp_, flush),
+                     self.capture_request_]
         return self.dispatch_functions(functions, wait, signal_function)
 
     def switch_mode_capture_request_and_stop(self, camera_config, wait=None, signal_function=None):

tests/test_list.txt

@@ -37,6 +37,7 @@ examples/still_capture_with_config.py
 examples/still_during_video.py
 examples/switch_mode.py
 examples/switch_mode_2.py
+examples/timestamp_capture.py
 examples/title_bar.py
 examples/tuning_file.py
 examples/video_with_config.py