解释WAV数据

Question

我正在尝试编写一个显示PCM数据的程序.我一直非常沮丧地试图找到一个具有正确抽象级别的库,但我找到了python wave库并且一直在使用它.但是,我不确定如何解释数据.

wave.getparams函数返回(2个通道,2个字节,44100 Hz,96333帧,无压缩,无压缩).这一切看起来都很愉快,但后来我尝试打印一个帧:'\ xc0\xff\xd0\xff'这是4个字节.我想一个帧可能是2个样本,但模糊不会在那里结束.

96333帧*2个样本/帧*(1/44.1k秒/样本)= 4.3688秒

然而,iTunes报告时间接近2秒,基于文件大小和比特率的计算在2.7秒的范围内.这里发生了什么？

另外,我怎么知道字节是有符号还是无符号？

非常感谢!

Answer 1

谢谢您的帮助!我得到了它的工作,我会在这里发布解决方案供大家使用,以防其他一些可怜的灵魂需要它:

import wave
import struct

def pcm_channels(wave_file):
    """Given a file-like object or file path representing a wave file,
    decompose it into its constituent PCM data streams.

    Input: A file like object or file path
    Output: A list of lists of integers representing the PCM coded data stream channels
        and the sample rate of the channels (mixed rate channels not supported)
    """
    stream = wave.open(wave_file,"rb")

    num_channels = stream.getnchannels()
    sample_rate = stream.getframerate()
    sample_width = stream.getsampwidth()
    num_frames = stream.getnframes()

    raw_data = stream.readframes( num_frames ) # Returns byte data
    stream.close()

    total_samples = num_frames * num_channels

    if sample_width == 1: 
        fmt = "%iB" % total_samples # read unsigned chars
    elif sample_width == 2:
        fmt = "%ih" % total_samples # read signed 2 byte shorts
    else:
        raise ValueError("Only supports 8 and 16 bit audio formats.")

    integer_data = struct.unpack(fmt, raw_data)
    del raw_data # Keep memory tidy (who knows how big it might be)

    channels = [ [] for time in range(num_channels) ]

    for index, value in enumerate(integer_data):
        bucket = index % num_channels
        channels[bucket].append(value)

    return channels, sample_rate

Answer 2

"两个通道"意味着立体声,因此将每个通道的持续时间相加是没有意义的 - 所以你关闭了两倍(2.18秒,而不是4.37).至于签名,正如这里所解释的,我引用:

8位采样存储为无符号字节,范围从0到255. 16位采样存储为2的补码有符号整数,范围从-32768到32767.

这是WAV格式规范的一部分(实际上是其超集RIFF),因此不依赖于您用来处理WAV文件的库.