ios audio playback technologies

最新推荐文章于 2017-06-16 09:45:12 发布

最新推荐文章于 2017-06-16 09:45:12 发布 · 79 阅读

本文介绍了不同音频技术下处理音频中断的方法。使用AVFoundation框架时，系统会自动暂停播放或录音并提供委托方法来通知应用程序中断的开始和结束。对于AudioQueueServices及I/O音频单元技术，开发者需要自行实现中断监听回调函数或使用AVAudioSession中断委托方法来保存和恢复播放位置，并重新激活音频会话。使用OpenAL进行播放时，除了实现上述方法外，还需要管理OpenAL上下文。SystemSoundServices播放的声音在中断时会静音并在中断结束后自动恢复。

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Table 3-2Audio interruption handling techniques according to audio technology
Audio technology	How interruptions work
AVFoundationframework	The`AVAudioPlayer`and`AVAudioRecorder`classes provide delegate methods for interruption start and end. Implement these methods to update your user interface and optionally, after interruption ends, to resume paused playback. The system automatically pauses playback or recording upon interruption, and reactivates your audio session when you resume playback or recording. If you want to save and restore playback position between application launches, save playback position on interruption as well as on application quit.
Audio Queue Services, I/O audio unit	These technologies put your application in control of handling interruptions. You are responsible for saving playback or recording position and reactivating your audio session after interruption ends. As explained in“Responding to Audio Session Interruptions,”implement the`AVAudioSession`interruption delegate methods or write an interruption listener callback function. If using these technologies for hardware-assisted encoding to AAC, refer to“Hardware-Assisted Codecs and Audio Interruptions.”
OpenAL	When using OpenAL for playback, implement the`AVAudioSession`interruption delegate methods or write an interruption listener callback function—as when using Audio Queue Services. However, the delegate or callback must additionally manage the OpenAL context. See“OpenAL and Audio Interruptions.”
System Sound Services	Sounds played using System Sound Services go silent when an interruption starts. They can automatically be used again if the interruption ends. Applications cannot influence the interruption behavior for sounds that use this playback technology.