Record timestamp when adding frames to stream

src/openflexure_microscope_server/things/camera/__init__.py

@@ -216,6 +216,41 @@ class CaptureGalleryInfo(BaseModel):
     card_type: Literal["Capture"] = "Capture"
 
 
+class MJPEGStreamWithTimestamp(lt.outputs.MJPEGStream):
+    """An MJPEG stream where the frame time can be recorded with the frame.
+
+    This can be used to capture when the image was taken by the sensor if known
+    rather than take the time it is added into the ring buffer.
+    """
+
+    def add_frame(self, frame: bytes, timestamp: Optional[datetime]) -> None:
+        """Add a JPEG to the MJPEG stream.
+
+        Modify the standard function to have an option to send in the capture time.
+
+        :param frame: The frame to add
+        :param timestamp: The time the frame was captured.
+
+        :raise ValueError: if the supplied frame does not start with the JPEG
+            start bytes and end with the end bytes.
+        """
+        if not (
+            frame[0] == 0xFF
+            and frame[1] == 0xD8
+            and frame[-2] == 0xFF
+            and frame[-1] == 0xD9
+        ):
+            raise ValueError("Invalid JPEG")
+        with self._lock:
+            entry = self._ringbuffer[(self.last_frame_i + 1) % len(self._ringbuffer)]
+            entry.timestamp = timestamp if timestamp is not None else datetime.now()
+            entry.frame = frame
+            entry.index = self.last_frame_i + 1
+            self._thing_server_interface.start_async_task_soon(
+                self.notify_new_frame, entry.index
+            )
+
+
 class BaseCamera(OFMThing, ABC):
     """The base class for all cameras. All cameras must directly inherit from this class.