2012/05/04 22:22
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AAC: Advanced Audio Coding codec (as well as both profiles of HE-AAC, High Efficiency AAC), .m4a (audio/m4a) or.3gp (audio/3gpp) files. AAC is a popular standard that is used by the iPod and other portable media players. Android supports this audio format inside of MPEG-4 audio files and inside of 3GP files (which are based on the MPEG-4 
format). Recent additions to the AAC specification, High Efficiency AAC are also supported. 

AAC(Advanced Audio Coding),中文称为“高级音频编码”,出现于1997年,基于 MPEG-2的音频编码技术。




MP3: MPEG-1 Audio Layer 3, .mp3 (audio/mp3) files. MP3, probably the most widely used audio codec, is supported. This allows Android to utilize the vast majority of audio available online through various web sites and music stores. 

MP3是一种音频压缩技术,其全称是动态影像专家压缩标准音频层面3(Moving Picture Experts Group Audio Layer III),简称为MP3。它被设计用来大幅度地降低音频数据量。利用 MPEG Audio Layer 3 的技术,将音乐以1:10 甚至 1:12 的压缩率,压缩成容量较小的文件,而对于大多数用户来说重放的音质与最初的不压缩音频相比没有明显的下降。

根据MPEG规范的说法,MPEG-4中的AAC(Advanced audio coding)将是MP3格式的下一代。MP3还分为耳机MP3和外放MP3两大类,传统MP3需要带耳机才有很好的音质,但是对人们的耳膜有所伤害,新型的MP3主要方向是外放MP3,对耳膜几乎没有任何伤害,从而得到人们的喜爱。

AMR: Adaptive Multi-Rate codec (both AMR Narrowband, AMR-NB, and AMR Wideband, AMR-WB),  .3gp (audio/3gpp) or .amr (audio/amr) files. AMR is the audio codec that has been standardized as the primary voice audio codec in use by the 3GPP (3rd Generation Partnership Project). The 3GPP is a telecommunications industry organization that creates specifications for the partner companies to use. In other words, the AMR codec is what is primarily used for voice 
calling applications on modern mobile phones and generally supported across mobile handset manufacturers and carriers. As such, this codec is generally useful for voice encoding but doesn’t perform well for more complex types of audio such as music. 
全称Adaptive Multi-Rate和Adaptive Multi-Rate Wideband,主要用于 移动设备的音频,压缩比比较大,但相对其他的 压缩格式质量比较差,由于多用于人声,通话,效果还是很不错的。

Ogg : Ogg Vorbis, .ogg (application/ogg) files. Ogg Vorbis is an open source, patent-free audio codec with quality that is comparable to commercial and patent-encumbered codecs such as MP3 and AAC. It was developed by volunteers and is currently maintained by the Xiph.Org foundation. 
Ogg全称应该是OGGVobis(oggVorbis)是一种新的 音频压缩格式,类似于MP3等的音乐格式。Ogg是完全免费、开放和没有专利限制的。OggVorbis文件的扩展名是.OGG。Ogg 文件格式可以不断地进行大小和 音质的改良,而不影响旧有的编码器或 播放器

PCM: Pulse Code Modulation commonly used in WAVE or WAV files (Waveform Audio Format), .wav (audio/x-wav) files. PCM is the technique used for storing audio on computers and other digital audio devices. It is generally an uncompressed audio file with data that represents the amplitude of a piece of audio over time. The “sample rate” is how often an amplitude reading is stored. The “bit-depth” is how many bits are used to represent an individual sample. A piece of audio data with a sample rate of 16kHz and a bit-depth of 32 bits means that it will contain 32 bits of data representing the amplitude of the audio and it will have 16,000 of these per second. The higher the sample rate and the higher the bit-depth, the more accurate the digitization of the audio is. Sample rate and bit-depth also determine how large the audio file will be when its length is taken into account. Android supports PCM audio data within WAV files. WAV is a long-standing standard audio format on PCs. 

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