1 # Copyright 2014 The Chromium Authors. All rights reserved. 2 # Use of this source code is governed by a BSD-style license that can be 3 # found in the LICENSE file. 4 5 import abc 6 7 8 class FrameReadError(Exception): 9 pass 10 11 12 class FrameGenerator(object): 13 """ Defines an interface for reading input frames. 14 15 Attributes: 16 _generator: A reference to the created generator. 17 """ 18 __metaclass__ = abc.ABCMeta 19 20 def __init__(self): 21 """ Initializes the FrameGenerator object. """ 22 self._generator = self._CreateGenerator() 23 24 @abc.abstractmethod 25 def _CreateGenerator(self): 26 """ Creates a new generator. 27 28 Implemented in derived classes. 29 30 Raises: 31 FrameReadError: A error occurred in reading the frame. 32 """ 33 raise NotImplementedError 34 35 @property 36 def Generator(self): 37 """ Returns: 38 A reference to the created generator. 39 """ 40 return self._generator 41 42 @abc.abstractproperty 43 def CurrentTimestamp(self): 44 """ Returns: 45 float, The timestamp of the current frame in milliseconds. 46 """ 47 raise NotImplementedError 48 49 @abc.abstractproperty 50 def CurrentFrameNumber(self): 51 """ Returns: 52 int, The frame index of the current frame. 53 """ 54 raise NotImplementedError 55 56 @abc.abstractproperty 57 def Dimensions(self): 58 """ Returns: 59 The dimensions of the frame sequence as a tuple int (width, height). 60 This value should be constant across frames. 61 """ 62 raise NotImplementedError 63
