| import cv2 | |
| class Timeline(object): | |
| """ | |
| The Timeline represents a logical sequence of frames, where the | |
| rendering of frames from the video stream will be done through | |
| lazy evaluation. | |
| """ | |
| reader_head = 0 | |
| def __init__(self, stream): | |
| """ | |
| Default Initializer | |
| :param stream: the video stream from OpenCV | |
| """ | |
| self.stream = stream | |
| self.len = stream.get(cv2.CAP_PROP_FRAME_COUNT) | |
| self.fps = stream.get(cv2.CAP_PROP_FPS) | |
| def next_frame(self): | |
| """ | |
| This method reads the next frame from the video stream and | |
| append it to the rendered_frames list. It also increments the | |
| reader_head by 1. | |
| :return: Usually the recently evaluated frame. | |
| If the video stream has been completely read, it will return | |
| None | |
| """ | |
| ret, frame = self.stream.read() | |
| self.reader_head += 1 | |
| if not ret: | |
| return None | |
| return frame | |
| def get_frame(self, pos): | |
| """ | |
| Returns the frame at the given position of the frame sequence | |
| :param pos: the position of the frame in the sequence | |
| :return: the frame at the specified position | |
| """ | |
| assert pos >= 0 | |
| self.stream.set(cv2.CAP_PROP_POS_FRAMES, self.len - 1) | |
| _, frame = self.stream.read() | |
| self.reader_head = pos + 1 | |
| return frame | |
| def get_frames(self, start, end): | |
| """ | |
| Returns the list of frames at between the specified start and | |
| end position in the frame sequence. | |
| :param start: Where the frame sequence should start | |
| :param end: Where the frame sequence should end | |
| :return: the frame sequence from start to end | |
| """ | |
| assert end >= start | |
| assert start >= 0 | |
| result = [] | |
| for i in xrange(start, end, 1): | |
| result.append(self.get_frame(i)) | |
| return result | |
| def release_stream(self): | |
| self.stream.release() | |
| class SlidingWindow(object): | |
| """ | |
| This class represents an adaptive sliding window. Meaning | |
| that it has a pointer to the start position of the window | |
| and its size. The size of the window can be changed at any | |
| time. Move operations and shrink and expand operations are | |
| included. | |
| """ | |
| def __init__(self, timeline, pos=0, size=2): | |
| """ | |
| Default Initializer for the sliding window | |
| :param timeline: the timeline where the sliding window | |
| should be applied | |
| :param pos: the position where the beginning of the | |
| window points to | |
| :param size: the size of the window | |
| """ | |
| self.timeline = timeline | |
| self.pos = pos | |
| self.size = size | |
| def move_right(self): | |
| """ | |
| This method does this: | |
| ░|░|█|█|░|░ => ░|░|░|█|█|░ | |
| 1 2 3 4 5 6 1 2 3 4 5 6 | |
| :return: the changed list of frame | |
| """ | |
| self.pos += 1 | |
| def move_left(self): | |
| """ | |
| This method does this: | |
| ░|░|█|█|░|░ => ░|█|█|░|░|░ | |
| 1 2 3 4 5 6 1 2 3 4 5 6 | |
| :return: the changed list of frame | |
| """ | |
| self.pos -= 1 | |
| def shrink_from_left(self): | |
| """ | |
| This method does this: | |
| ░|░|█|█|░|░ => ░|░|░|█|░|░ | |
| 1 2 3 4 5 6 1 2 3 4 5 6 | |
| :return: the changed list of frame | |
| """ | |
| self.pos += 1 | |
| self.size -= 1 | |
| def shrink_from_right(self): | |
| """ | |
| This method does this: | |
| ░|░|█|█|░|░ => ░|░|█|░|░|░ | |
| 1 2 3 4 5 6 1 2 3 4 5 6 | |
| :return: the changed list of frame | |
| """ | |
| self.size -= 1 | |
| def expand_to_left(self): | |
| """ | |
| This method does this: | |
| ░|░|█|█|░|░ => ░|█|█|█|░|░ | |
| 1 2 3 4 5 6 1 2 3 4 5 6 | |
| :return: the changed list of frame | |
| """ | |
| self.pos -= 1 | |
| self.size += 1 | |
| def expand_to_right(self): | |
| """ | |
| This method does$$ this: | |
| ░|░|█|█|░|░ => ░|░|█|█|█|░ | |
| 1 2 3 4 5 6 1 2 3 4 5 6 | |
| :return: the changed list of frame | |
| """ | |
| self.size += 1 | |
| def get_frames(self): | |
| """ | |
| Retrieves all the frames that are currently in this adaptive | |
| sliding window. | |
| :return: the frames in the sliding window | |
| """ | |
| return self.timeline.get_frames(self.pos, self.pos + self.size) | |
| def get_frame(self, pos): | |
| return self.timeline.get_frame(self.pos) | |
| def get_start_frame(self): | |
| return self.timeline.get_frame(self.pos) | |
| def get_end_frame(self): | |
| return self.timeline.get_frame(self.pos + self.size - 1) | |
| def at_end(self): | |
| return self.pos + self.size == self.timeline.len | |