1 #!/usr/bin/env python3.4 2 # 3 # Copyright 2017 - The Android Open Source Project 4 # 5 # Licensed under the Apache License, Version 2.0 (the "License"); 6 # you may not use this file except in compliance with the License. 7 # You may obtain a copy of the License at 8 # 9 # http://www.apache.org/licenses/LICENSE-2.0 10 # 11 # Unless required by applicable law or agreed to in writing, software 12 # distributed under the License is distributed on an "AS IS" BASIS, 13 # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 14 # See the License for the specific language governing permissions and 15 # limitations under the License. 16 """This module provides abstraction of audio data.""" 17 18 import contextlib 19 import copy 20 import numpy 21 import struct 22 from io import StringIO 23 """The dict containing information on how to parse sample from raw data. 24 25 Keys: The sample format as in aplay command. 26 Values: A dict containing: 27 message: Human-readable sample format. 28 dtype_str: Data type used in numpy dtype. Check 29 https://docs.scipy.org/doc/numpy/reference/arrays.dtypes.html 30 for supported data type. 31 size_bytes: Number of bytes for one sample. 32 """ 33 SAMPLE_FORMATS = dict( 34 S32_LE=dict( 35 message='Signed 32-bit integer, little-endian', 36 dtype_str='<i', 37 size_bytes=4), 38 S16_LE=dict( 39 message='Signed 16-bit integer, little-endian', 40 dtype_str='<i', 41 size_bytes=2)) 42 43 44 def get_maximum_value_from_sample_format(sample_format): 45 """Gets the maximum value from sample format. 46 47 Args: 48 sample_format: A key in SAMPLE_FORMAT. 49 50 Returns:The maximum value the sample can hold + 1. 51 52 """ 53 size_bits = SAMPLE_FORMATS[sample_format]['size_bytes'] * 8 54 return 1 << (size_bits - 1) 55 56 57 class AudioRawDataError(Exception): 58 """Error in AudioRawData.""" 59 pass 60 61 62 class AudioRawData(object): 63 """The abstraction of audio raw data. 64 65 @property channel: The number of channels. 66 @property channel_data: A list of lists containing samples in each channel. 67 E.g., The third sample in the second channel is 68 channel_data[1][2]. 69 @property sample_format: The sample format which should be one of the keys 70 in audio_data.SAMPLE_FORMATS. 71 """ 72 73 def __init__(self, binary, channel, sample_format): 74 """Initializes an AudioRawData. 75 76 Args: 77 binary: A string containing binary data. If binary is not None, 78 The samples in binary will be parsed and be filled into 79 channel_data. 80 channel: The number of channels. 81 sample_format: One of the keys in audio_data.SAMPLE_FORMATS. 82 """ 83 self.channel = channel 84 self.channel_data = [[] for _ in range(self.channel)] 85 self.sample_format = sample_format 86 if binary: 87 self.read_binary(binary) 88 89 def read_binary(self, binary): 90 """Reads samples from binary and fills channel_data. 91 92 Reads samples of fixed width from binary string into a numpy array 93 and shapes them into each channel. 94 95 Args: 96 binary: A string containing binary data. 97 """ 98 sample_format_dict = SAMPLE_FORMATS[self.sample_format] 99 100 # The data type used in numpy fromstring function. For example, 101 # <i4 for 32-bit signed int. 102 np_dtype = '%s%d' % (sample_format_dict['dtype_str'], 103 sample_format_dict['size_bytes']) 104 105 # Reads data from a string into 1-D array. 106 np_array = numpy.fromstring(binary, dtype=np_dtype) 107 108 n_frames = len(np_array) / self.channel 109 # Reshape np_array into an array of shape (n_frames, channel). 110 np_array = np_array.reshape(int(n_frames), self.channel) 111 # Transpose np_arrya so it becomes of shape (channel, n_frames). 112 self.channel_data = np_array.transpose() 113
