SpeakHere

SpeakHere给出了关于AudioQueue Services, Audio File Services, 以及 AudioSession Services在录音和播放过程中的具体用法.

具体使用是使用场景:

• The code in SpeakHere uses Audio File Services to create, record into, and read from a CAF (Core Audio Format) audio file containing uncompressed (PCM) audio data.
• The application uses Audio Queue Services to manage recording and playback.
• The application also uses Audio Session Services to manage interruptions and audio hardware route changes (as described in Core Audio Overview).

简而言之,Audio File Services读写CAF文件(内部是PCM data),Audio Queue Services用来录音和播放,Audio Session Services监听打断录音或播放的事件.

关于测试

在AQRecorder.mm代码中的SetupAudioFormat参数用来修改录音的格式.

如果需要测试AudioSession Service相关功能:

• To test the application's interruption behavior, place a phone call to the device during recording or playback; then choose to ignore the phone call.
• To test the application's audio hardware route change behavior, plug in or unplug a headset while playing back or recording.

具体实现的功能

• Set up a linear PCM audio format.设置成LPCM音频格式数据
• Set up a compressed audio format.设置成系统中支持的压缩的音频数据
• Create a Core Audio Format (CAF) audio file and save it to an application's Documents directory.创建和保存CAF文件
• Reuse an existing CAF file by overwriting it.
• Read from a CAF file for playback.从CAF文件中读取音频数据然后播放
• Create and use recording (input) and playback (output) audio queue objects.创建audioQueue(录音和播放)
• Define and use audio data and property data callbacks with audio queue objects.通过audioQueue 的callback获取录音或播放的音频数据
• Set playback gain for an audio queue object.播放增强
• Stop recording in a way ensures that all audio data gets written to disk. 停止录音时候,确保所有的audio data已经写入文件系统
• Stop playback when a sound file has finished playing.
• Stop playback immediately when a user invokes a Stop method.
• Enable audio level metering in an audio queue object.
• Get average and peak audio levels from a running audio queue object. 获取平均和峰值音量
• Use audio format magic cookies with an audio queue object.获取audioQueue对象的幻数
• Use OpenGL to indicate average and peak recording and playback level.使用OpenGL绘制平均和峰值音量
• Use Audio Session Services to register an interruption callback.
• Use Audio Session Services to register property listener callback.
• Use Audio Session Services to set appropriate audio session categories for recording and playback.
• Use Audio Session Services to pause playback upon receiving an interruption, and to then resume playback if the interruption ends.
• Use UIBarButtonItem objects as toggle buttons.

注意iOS默认支持的audio Formats

• linear PCM
• ALAC (Apple Lossless)
• IMA4 (IMA/ADPCM)
• iLBC
• µLaw
• aLaw

因此如果需要保存成其他的音频格式,需要自己使用LPCM,然后封装成其他的音频格式,例如使用Speex压缩,Ogg封装,进行语音传递.