iOS：如何将音频文件读入浮动缓冲区

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问题描述

我有一个非常短的音频文件，例如10秒钟（比如说）.PCM格式

I have a really short audio file, say a 10th of a second in (say) .PCM format

我想使用RemoteIO重复循环文件产生连续的音乐基调。那么如何将其读入浮点数组呢？

I want to use RemoteIO to loop through the file repeatedly to produce a continuous musical tone. So how do I read this into an array of floats?

编辑：虽然我可以挖出文件格式，将文件解压缩到NSData并手动处理，我猜测有一种更明智的通用方法......（例如应对不同的格式）

while I could probably dig out the file format, extract the file into an NSData and process it manually, I'm guessing there is a more sensible generic approach... ( that eg copes with different formats )

推荐答案

你可以使用ExtAudioFile以多种客户端格式从任何支持的数据格式读取数据。下面是一个将文件读取为16位整数的示例：

You can use ExtAudioFile to read data from any supported data format in numerous client formats. Here is an example to read a file as 16-bit integers:

CFURLRef url = /* ... */;
ExtAudioFileRef eaf;
OSStatus err = ExtAudioFileOpenURL((CFURLRef)url, &eaf);
if(noErr != err)
  /* handle error */

AudioStreamBasicDescription format;
format.mSampleRate = 44100;
format.mFormatID = kAudioFormatLinearPCM;
format.mFormatFlags = kAudioFormatFormatFlagIsPacked;
format.mBitsPerChannel = 16;
format.mChannelsPerFrame = 2;
format.mBytesPerFrame = format.mChannelsPerFrame * 2;
format.mFramesPerPacket = 1;
format.mBytesPerPacket = format.mFramesPerPacket * format.mBytesPerFrame;

err = ExtAudioFileSetProperty(eaf, kExtAudioFileProperty_ClientDataFormat, sizeof(format), &format);

/* Read the file contents using ExtAudioFileRead */

如果你想要Float32数据，您可以设置格式，如下所示：

If you wanted Float32 data, you would set up format like this:

format.mFormatID = kAudioFormatLinearPCM;
format.mFormatFlags = kAudioFormatFlagsNativeFloatPacked;
format.mBitsPerChannel = 32;

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