可在 Windows Media Player 上播放的 iPhone 压缩音频格式

发布于 2024-08-10 04:54:15 字数 189 浏览 7 评论 0原文

我必须在 iPhone 上录制音频，然后在 Windows Media Player 上播放，不使用非标准编解码器；也就是说，不使用 WMP 中未附带的编解码器。（公司要求。）音频必须以 base-64 传输到服务器，因此我需要使音频大小尽可能小。即使在 8Kb 录制频率下，AIFF 文件也会占用大量空间。我似乎找不到 WMP 可以吞下的压缩 AIFF 格式。

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终难愈 2024-08-17 04:54:15

最好的选择是使用 ulaw 或 alaw 压缩编写 WAV 文件（AudioStreamBasicDescription 的 mFormatId 将为 kAudioFormatULaw 或 kAudioFormatALaw >. 测试一下哪一个为您的应用程序提供了最小的文件大小。

下面是一些设置 ExtAudioFile 实例来编写 ulaw 的代码：

NSArray * docs = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
NSString * docDir = [docs objectAtIndex:0]; 
NSURL * outFile = [NSURL fileURLWithPath:[docDir stringByAppendingPathComponent:@"OutFile.wav"]];
AudioStreamBasicDescription asbd;
bzero(&asbd, sizeof(asbd));
asbd.mSampleRate = 11025; // or whatever
asbd.mFramesPerPacket = 1;
asbd.mChannelsPerFrame = 1;
asbd.mFormatID = kAudioFormatULaw; //or kAudioFormatALaw
ExtAudioFileRef theFile;
err = ExtAudioFileCreateWithURL((CFURLRef)outFile,
                          kAudioFileWAVEType,
                          &asbd,
                          0,
                          kAudioFileFlags_EraseFile,
                          &theFile);

希望有所帮助

--- 添加 ---

以下是对 SpeakHere 示例代码的修改。获取 ulaw 压缩：

SpeakHereController.mm:116

recordFilePath = (CFStringRef)[NSTemporaryDirectory() stringByAppendingPathComponent: @"recordedFile.wav"];

SpeakHereController.mm:158

recorder->startRecord(CFSTR("recordedFile.wav"));

AQRecorder.mm:192

SetupAudioFormat(kAudioFormatULaw);

AQRecorder.mm:215

XThrowIfError(AudioFileCreateWithURL(url, kAudioFileWAVEType, &mRecordFormat, kAudioFileFlags_EraseFile,
                                      &mRecordFile), "AudioFileCreateWithURL failed");

Best bet is to write WAV files with ulaw or alaw compression (the mFormatId of your AudioStreamBasicDescription would be kAudioFormatULaw or kAudioFormatALaw. Test to see which one gives you the smallest file sizes for your application.

Here's some code to set up an ExtAudioFile instance to write ulaw:

NSArray * docs = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
NSString * docDir = [docs objectAtIndex:0]; 
NSURL * outFile = [NSURL fileURLWithPath:[docDir stringByAppendingPathComponent:@"OutFile.wav"]];
AudioStreamBasicDescription asbd;
bzero(&asbd, sizeof(asbd));
asbd.mSampleRate = 11025; // or whatever
asbd.mFramesPerPacket = 1;
asbd.mChannelsPerFrame = 1;
asbd.mFormatID = kAudioFormatULaw; //or kAudioFormatALaw
ExtAudioFileRef theFile;
err = ExtAudioFileCreateWithURL((CFURLRef)outFile,
                          kAudioFileWAVEType,
                          &asbd,
                          0,
                          kAudioFileFlags_EraseFile,
                          &theFile);

Hope that helps.

--- ADDED ---

Here are modifications to the SpeakHere sample code to get ulaw compression:

SpeakHereController.mm:116

recordFilePath = (CFStringRef)[NSTemporaryDirectory() stringByAppendingPathComponent: @"recordedFile.wav"];

SpeakHereController.mm:158

recorder->startRecord(CFSTR("recordedFile.wav"));

AQRecorder.mm:192

SetupAudioFormat(kAudioFormatULaw);

AQRecorder.mm:215

XThrowIfError(AudioFileCreateWithURL(url, kAudioFileWAVEType, &mRecordFormat, kAudioFileFlags_EraseFile,
                                      &mRecordFile), "AudioFileCreateWithURL failed");

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