Reference for ultralytics/engine/predictor.py

def __call__(self, source=None, model=None, stream=False, *args, **kwargs):
    """Performs inference on an image or stream."""
    self.stream = stream
    if stream:
        return self.stream_inference(source, model, *args, **kwargs)
    else:
        return list(self.stream_inference(source, model, *args, **kwargs))  # merge list of Result into one

def add_callback(self, event: str, func):
    """Add callback."""
    self.callbacks[event].append(func)

def inference(self, im, *args, **kwargs):
    """Runs inference on a given image using the specified model and arguments."""
    visualize = (
        increment_path(self.save_dir / Path(self.batch[0][0]).stem, mkdir=True)
        if self.args.visualize and (not self.source_type.tensor)
        else False
    )
    return self.model(im, augment=self.args.augment, visualize=visualize, embed=self.args.embed, *args, **kwargs)

def postprocess(self, preds, img, orig_imgs):
    """Post-processes predictions for an image and returns them."""
    return preds

def pre_transform(self, im):
    """
    Pre-transform input image before inference.

    Args:
        im (List(np.ndarray)): (N, 3, h, w) for tensor, [(h, w, 3) x N] for list.

    Returns:
        (list): A list of transformed images.
    """
    same_shapes = len({x.shape for x in im}) == 1
    letterbox = LetterBox(self.imgsz, auto=same_shapes and self.model.pt, stride=self.model.stride)
    return [letterbox(image=x) for x in im]

def predict_cli(self, source=None, model=None):
    """
    Method used for Command Line Interface (CLI) prediction.

    This function is designed to run predictions using the CLI. It sets up the source and model, then processes
    the inputs in a streaming manner. This method ensures that no outputs accumulate in memory by consuming the
    generator without storing results.

    Note:
        Do not modify this function or remove the generator. The generator ensures that no outputs are
        accumulated in memory, which is critical for preventing memory issues during long-running predictions.
    """
    gen = self.stream_inference(source, model)
    for _ in gen:  # sourcery skip: remove-empty-nested-block, noqa
        pass

def preprocess(self, im):
    """
    Prepares input image before inference.

    Args:
        im (torch.Tensor | List(np.ndarray)): BCHW for tensor, [(HWC) x B] for list.
    """
    not_tensor = not isinstance(im, torch.Tensor)
    if not_tensor:
        im = np.stack(self.pre_transform(im))
        im = im[..., ::-1].transpose((0, 3, 1, 2))  # BGR to RGB, BHWC to BCHW, (n, 3, h, w)
        im = np.ascontiguousarray(im)  # contiguous
        im = torch.from_numpy(im)

    im = im.to(self.device)
    im = im.half() if self.model.fp16 else im.float()  # uint8 to fp16/32
    if not_tensor:
        im /= 255  # 0 - 255 to 0.0 - 1.0
    return im

def run_callbacks(self, event: str):
    """Runs all registered callbacks for a specific event."""
    for callback in self.callbacks.get(event, []):
        callback(self)

def save_predicted_images(self, save_path="", frame=0):
    """Save video predictions as mp4 at specified path."""
    im = self.plotted_img

    # Save videos and streams
    if self.dataset.mode in {"stream", "video"}:
        fps = self.dataset.fps if self.dataset.mode == "video" else 30
        frames_path = f'{save_path.split(".", 1)[0]}_frames/'
        if save_path not in self.vid_writer:  # new video
            if self.args.save_frames:
                Path(frames_path).mkdir(parents=True, exist_ok=True)
            suffix, fourcc = (".mp4", "avc1") if MACOS else (".avi", "WMV2") if WINDOWS else (".avi", "MJPG")
            self.vid_writer[save_path] = cv2.VideoWriter(
                filename=str(Path(save_path).with_suffix(suffix)),
                fourcc=cv2.VideoWriter_fourcc(*fourcc),
                fps=fps,  # integer required, floats produce error in MP4 codec
                frameSize=(im.shape[1], im.shape[0]),  # (width, height)
            )

        # Save video
        self.vid_writer[save_path].write(im)
        if self.args.save_frames:
            cv2.imwrite(f"{frames_path}{frame}.jpg", im)

    # Save images
    else:
        cv2.imwrite(save_path, im)

def setup_model(self, model, verbose=True):
    """Initialize YOLO model with given parameters and set it to evaluation mode."""
    self.model = AutoBackend(
        weights=model or self.args.model,
        device=select_device(self.args.device, verbose=verbose),
        dnn=self.args.dnn,
        data=self.args.data,
        fp16=self.args.half,
        batch=self.args.batch,
        fuse=True,
        verbose=verbose,
    )

    self.device = self.model.device  # update device
    self.args.half = self.model.fp16  # update half
    self.model.eval()

def setup_source(self, source):
    """Sets up source and inference mode."""
    self.imgsz = check_imgsz(self.args.imgsz, stride=self.model.stride, min_dim=2)  # check image size
    self.transforms = (
        getattr(
            self.model.model,
            "transforms",
            classify_transforms(self.imgsz[0], crop_fraction=self.args.crop_fraction),
        )
        if self.args.task == "classify"
        else None
    )
    self.dataset = load_inference_source(
        source=source,
        batch=self.args.batch,
        vid_stride=self.args.vid_stride,
        buffer=self.args.stream_buffer,
    )
    self.source_type = self.dataset.source_type
    if not getattr(self, "stream", True) and (
        self.source_type.stream
        or self.source_type.screenshot
        or len(self.dataset) > 1000  # many images
        or any(getattr(self.dataset, "video_flag", [False]))
    ):  # videos
        LOGGER.warning(STREAM_WARNING)
    self.vid_writer = {}

def show(self, p=""):
    """Display an image in a window using OpenCV imshow()."""
    im = self.plotted_img
    if platform.system() == "Linux" and p not in self.windows:
        self.windows.append(p)
        cv2.namedWindow(p, cv2.WINDOW_NORMAL | cv2.WINDOW_KEEPRATIO)  # allow window resize (Linux)
        cv2.resizeWindow(p, im.shape[1], im.shape[0])  # (width, height)
    cv2.imshow(p, im)
    cv2.waitKey(300 if self.dataset.mode == "image" else 1)  # 1 millisecond

@smart_inference_mode()
def stream_inference(self, source=None, model=None, *args, **kwargs):
    """Streams real-time inference on camera feed and saves results to file."""
    if self.args.verbose:
        LOGGER.info("")

    # Setup model
    if not self.model:
        self.setup_model(model)

    with self._lock:  # for thread-safe inference
        # Setup source every time predict is called
        self.setup_source(source if source is not None else self.args.source)

        # Check if save_dir/ label file exists
        if self.args.save or self.args.save_txt:
            (self.save_dir / "labels" if self.args.save_txt else self.save_dir).mkdir(parents=True, exist_ok=True)

        # Warmup model
        if not self.done_warmup:
            self.model.warmup(imgsz=(1 if self.model.pt or self.model.triton else self.dataset.bs, 3, *self.imgsz))
            self.done_warmup = True

        self.seen, self.windows, self.batch = 0, [], None
        profilers = (
            ops.Profile(device=self.device),
            ops.Profile(device=self.device),
            ops.Profile(device=self.device),
        )
        self.run_callbacks("on_predict_start")
        for self.batch in self.dataset:
            self.run_callbacks("on_predict_batch_start")
            paths, im0s, s = self.batch

            # Preprocess
            with profilers[0]:
                im = self.preprocess(im0s)

            # Inference
            with profilers[1]:
                preds = self.inference(im, *args, **kwargs)
                if self.args.embed:
                    yield from [preds] if isinstance(preds, torch.Tensor) else preds  # yield embedding tensors
                    continue

            # Postprocess
            with profilers[2]:
                self.results = self.postprocess(preds, im, im0s)
            self.run_callbacks("on_predict_postprocess_end")

            # Visualize, save, write results
            n = len(im0s)
            for i in range(n):
                self.seen += 1
                self.results[i].speed = {
                    "preprocess": profilers[0].dt * 1e3 / n,
                    "inference": profilers[1].dt * 1e3 / n,
                    "postprocess": profilers[2].dt * 1e3 / n,
                }
                if self.args.verbose or self.args.save or self.args.save_txt or self.args.show:
                    s[i] += self.write_results(i, Path(paths[i]), im, s)

            # Print batch results
            if self.args.verbose:
                LOGGER.info("\n".join(s))

            self.run_callbacks("on_predict_batch_end")
            yield from self.results

    # Release assets
    for v in self.vid_writer.values():
        if isinstance(v, cv2.VideoWriter):
            v.release()

    # Print final results
    if self.args.verbose and self.seen:
        t = tuple(x.t / self.seen * 1e3 for x in profilers)  # speeds per image
        LOGGER.info(
            f"Speed: %.1fms preprocess, %.1fms inference, %.1fms postprocess per image at shape "
            f"{(min(self.args.batch, self.seen), 3, *im.shape[2:])}" % t
        )
    if self.args.save or self.args.save_txt or self.args.save_crop:
        nl = len(list(self.save_dir.glob("labels/*.txt")))  # number of labels
        s = f"\n{nl} label{'s' * (nl > 1)} saved to {self.save_dir / 'labels'}" if self.args.save_txt else ""
        LOGGER.info(f"Results saved to {colorstr('bold', self.save_dir)}{s}")
    self.run_callbacks("on_predict_end")

def write_results(self, i, p, im, s):
    """Write inference results to a file or directory."""
    string = ""  # print string
    if len(im.shape) == 3:
        im = im[None]  # expand for batch dim
    if self.source_type.stream or self.source_type.from_img or self.source_type.tensor:  # batch_size >= 1
        string += f"{i}: "
        frame = self.dataset.count
    else:
        match = re.search(r"frame (\d+)/", s[i])
        frame = int(match[1]) if match else None  # 0 if frame undetermined

    self.txt_path = self.save_dir / "labels" / (p.stem + ("" if self.dataset.mode == "image" else f"_{frame}"))
    string += "%gx%g " % im.shape[2:]
    result = self.results[i]
    result.save_dir = self.save_dir.__str__()  # used in other locations
    string += f"{result.verbose()}{result.speed['inference']:.1f}ms"

    # Add predictions to image
    if self.args.save or self.args.show:
        self.plotted_img = result.plot(
            line_width=self.args.line_width,
            boxes=self.args.show_boxes,
            conf=self.args.show_conf,
            labels=self.args.show_labels,
            im_gpu=None if self.args.retina_masks else im[i],
        )

    # Save results
    if self.args.save_txt:
        result.save_txt(f"{self.txt_path}.txt", save_conf=self.args.save_conf)
    if self.args.save_crop:
        result.save_crop(save_dir=self.save_dir / "crops", file_name=self.txt_path.stem)
    if self.args.show:
        self.show(str(p))
    if self.args.save:
        self.save_predicted_images(str(self.save_dir / p.name), frame)

    return string