AVAudioFormat initStandardFormatWithSampleRate 是否返回不正确的流描述

Question

当尝试使用ExtAudioFileCreateWithURL编写PCM音频文件时，使用2声道音频格式(Mac OS X，SDK 10.10(时出现"fmt？"错误

我创建音频格式

[[AVAudioFormat alloc] initStandardFormatWithSampleRate:sampleRate channels:channelCount]

并将其用作我的应用程序中 AUGraph 的音频格式。

AUGraph适用于1声道和2声道格式，但是当尝试使用ExtAudioFileCreateWithURL编写音频文件时，它仅适用于1声道，2声道会导致"fmt？"错误。

运行以下测试时...

AVAudioFormat* ch1 = [[AVAudioFormat alloc] initStandardFormatWithSampleRate:44100. channels:1];
AVAudioFormat* ch2 = [[AVAudioFormat alloc] initStandardFormatWithSampleRate:44100. channels:2];
NSLog(@"ch1: %@", [ch1 description]);
NSLog(@"ch1 mBitsPerChannel: %d", ch1.streamDescription->mBitsPerChannel);
NSLog(@"ch1 mChannelsPerFrame: %d", ch1.streamDescription->mChannelsPerFrame);
NSLog(@"ch1 mBytesPerFrame: %d", ch1.streamDescription->mBytesPerFrame);
NSLog(@"ch1 mBytesPerPacket: %d", ch1.streamDescription->mBytesPerPacket);
NSLog(@"ch1 mFramesPerPacket: %d", ch1.streamDescription->mFramesPerPacket);
NSLog(@"ch2: %@", [ch2 description]);
NSLog(@"ch2 mBitsPerChannel: %d", ch2.streamDescription->mBitsPerChannel);
NSLog(@"ch2 mChannelsPerFrame: %d", ch2.streamDescription->mChannelsPerFrame);
NSLog(@"ch2 mBytesPerFrame: %d", ch2.streamDescription->mBytesPerFrame);
NSLog(@"ch2 mBytesPerPacket: %d", ch2.streamDescription->mBytesPerPacket);
NSLog(@"ch2 mFramesPerPacket: %d", ch2.streamDescription->mFramesPerPacket);

。这是控制台中的输出：

ch1: <AVAudioFormat 0x600000084560:  1 ch,  44100 Hz, Float32>
ch1 mBitsPerChannel: 32
ch1 mChannelsPerFrame: 1
ch1 mBytesPerFrame: 4
ch1 mBytesPerPacket: 4
ch1 mFramesPerPacket: 1
ch2: <AVAudioFormat 0x6000000845b0:  2 ch,  44100 Hz, Float32, non-inter>
ch2 mBitsPerChannel: 32
ch2 mChannelsPerFrame: 2
ch2 mBytesPerFrame: 4
ch2 mBytesPerPacket: 4
ch2 mFramesPerPacket: 1

mBytesPerFrame和mBytesPerPacket字段不应该有区别吗？还是我在这里错过了什么？

Answer 1

我想我发现了我的错误：

使用 ExtAudioFileCreateWithURL 写入 PCM 文件需要交错kExtAudioFileProperty_FileDataFormat。由于AVAudioFormat的 -initStandardFormatWithSampleRate:channelLayout:返回 Core Audio 的标准去交错 32 位浮点格式，我得到了"fmt？错误。

顺便说一句，将标准格式更改为交错，导致 mBytesPerFrame 和 mBytesPerPacket 的值为 8，当然......