iOS 支持的音頻播放格式：
*AAC
*HE-AAC
*AMR (Adaptive Multi-Rate, a format for speech)
*ALAC (Apple Lossless)
*iLBC (internet Low Bitrate Codec, another format for speech)
*IMA4 (IMA/ADPCM)
*linear PCM (uncompressed)
*μ-law and a-law
*MP3 (MPEG-1 audio layer 3）
iOS 支持的音頻錄製的 格式：
*AAC (on supported devices only)
*ALAC (Apple Lossless)
*iLBC (internet Low Bitrate Codec, for speech)
*IMA4 (IMA/ADPCM)
*linear PCM
*μ-law and a-law