FLAC介绍

introduction
引言
FLAC stands for Free Lossless Audio Codec, an audio format similar to MP3, but lossless, meaning that audio is compressed in FLAC without any loss in quality. This is similar to how Zip works, except with FLAC you will get much better compression because it is designed specifically for audio, and you can play back compressed FLAC files in your favorite player (or your car or home stereo, see supported devices) just like you would an MP3 file.

FLAC 是 Free Lossless Audio Codec （自由无损音频编解码器 ）的缩写，是一种类似于 MP3 的音频格式，但是是无损的，这意味着音频以 FLAC 的方式压缩在质量上没有任何损失。这种类似于 Zip 的工作方式，除了使用 FLAC ，你会得到更优质的压缩，因为它是特别为音频而设计，您也可以使用喜欢的播放器（或者汽车或者家用立体声，参考支持的设备）来播放压缩的 FLAC 文件，就像播放 MP3 文件一样。

FLAC stands out as the fastest and most widely supported lossless audio codec, and the only one that at once is non-proprietary, is unencumbered by patents, has an open-source reference implementation, has a well documented format and API, and has several other independent implementations.

FLAC 是一种杰出的能快速、广泛的支持无损音频编解码器，同时也是唯一一种没有专利、不受专利阻碍、具有开源参考实现、良好的文档格式和 API 以及其他几种独立实现的音频解码器。


FLAC supports tagging, cover art, and fast seeking. FLAC is freely available and supported on most operating systems, including Windows, "unix" (Linux, *BSD, Solaris, OS X, IRIX), BeOS, OS/2, and Amiga.

FLAC 支持标签、封面、快速搜索。 FLAC 可以免费获得、并且支持大部分操作系统，包括 Windows, unix (Linux, *BSD, Solaris, OS X, IRIX), BeOS, OS/2, 和 Amiga 。

There are many programs and devices that support FLAC, but the core FLAC project here maintains the format and provides programs and libraries for working with FLAC files. See Getting FLAC for instructions on downloading and installing the official FLAC tools, or Using FLAC for instructions and guides on playing FLAC files, ripping CDs to FLAC, etc.
有很多程序和设备支持 FLAC, 但是 FLAC 核心项目维护格式，并且为支持 FLAC 文件运行提供程序和库。请参考获取 FLAC 的下载和安装官方 FLAC 工具说明，或者使用 FLAC 的有关播放 FLAC 文件、将 CD 刻录到 FLAC 等方面的说明和指引。


When we say that FLAC is "Free" it means more than just that it is available at no cost. It means that the specification of the format is fully open to the public to be used for any purpose (the FLAC project reserves the right to set the FLAC specification and certify compliance), and that neither the FLAC format nor any of the implemented encoding/decoding methods are covered by any known patent. It also means that all the source code is available under open-source licenses. It is the first truly open and free lossless audio format. (For more information, see the license page.)
当我们说 FLAC 是“免费”的时候，这不仅仅意味着免费获得。它意味着这种格式的规范是完全对公众开放，供任何目的（ FLAC 项目保留设定 FLAC 规范和认证遵守的权利）的使用，而且任何已知专利都不涵盖 FLAC 格式或实现编码 / 解码的方法。这也意味着所有的源代码可以在有开源许可的情况下使用。这是第一个正真开放和自由无损音频的格式（更多的信息，请参阅许可页面）。


Notable features of FLAC:
FLAC 的显著特点：

 Lossless: The encoding of audio (PCM) data incurs no loss of information, and the decoded audio is bit-for-bit identical to what went into the encoder. Each frame contains a 16-bit CRC of the frame data for detecting transmission errors. The integrity of the audio data is further insured by storing an MD5 signature of the original unencoded audio data in the file header, which can be compared against later during decoding or testing.

无损：音频（ PCM ）数据的编码不会有信息丢失，解码后的音频与编码时的每一个字节完全相同。每一帧包 含 16 位的帧数据 CRC （注：循环冗余校验 CRC （ Cyclic Redundancy Check ）），用来检测传输错误。音频数据的完整性是通过原始的未编码的音频数据的 MD5 签名存储在文件头中来进一步保证，这些可以在解码和测试过程中相比较。

Fast: FLAC is asymmetric in favor of decode speed. Decoding requires only integer arithmetic, and is much less compute-intensive than for most perceptual codecs. Real-time decode performance is easily achievable on even modest hardware.
快速： FLAC 是不对称的有利于解码速度。解码只需要整数运算，比大多数感知编解码器的运算量（密集运算）小得多。实时解码性能很容易实现，即时是温和的硬件。

Hardware support: FLAC is supported by dozens of consumer electronic devices, from portable players, to home stereo equipment, to car stereo.
硬件支持： FLAC 需要数十个消费类电子设备支持，从便携式播放器，到家用立体声设备，再到汽车立体声。


Flexible metadata: FLAC's metadata system supports tags, cover art, seek tables, and cue sheets. Applications can write their own APPLICATION metadata once they register an ID. New metadata blocks can be defined and implemented in future versions of FLAC without breaking older streams or decoders.

灵活的元数据： FLAC 元数据系统支持标签，封面艺术、查找表，以及提示表。一旦应用程序注册了 ID ，就可以写入自己的应用元数据。新的元数据块在 FLAC 的未来版本中被定义和执行，不会破坏旧的线程或解码器。

Seekable: FLAC supports fast sample-accurate seeking. Not only is this useful for playback, it makes FLAC files suitable for use in editing applications.
可见的： FLAC 支持快速的样本精确查找。不仅仅是对录音回放有帮助，而且使 FLAC 文件适合用来编辑应用程序。


Streamable: Each FLAC frame contains enough data to decode that frame. FLAC does not even rely on previous or following frames. FLAC uses sync codes and CRCs (similar to MPEG and other formats), which, along with framing, allow decoders to pick up in the middle of a stream with a minimum of delay.
可重读：每个 FLAC 帧包含足够的数据来解码该帧。 FLAC 甚至不会依赖之前的或者接下的帧。 FLAC 使用同步编码和 CRCs( 与 MPEG 和其他格式类似 ) ，在帧化的同时，允许解码器以最小的延迟在音频流间拾取。


 Suitable for archiving: FLAC is an open format, and there is no generation loss if you need to convert your data to another format in the future. In addition to the frame CRCs and MD5 signature, flac has a verify option that decodes the encoded stream in parallel with the encoding process and compares the result to the original, aborting with an error if there is a mismatch.
适合存档： FLAC 是一种开放的格式，如果将来你需要将数据转换为其他格式，是不会有代损失。除了帧 CRCs 和 MD5 签名， FLAC 有一个验证选项，
该选项与编码过程并行解码编码流，并将结果与原始结果进行比较，如果不匹配就会终止错误。

Convenient CD archiving: FLAC has a "cue sheet" metadata block for storing a CD table of contents and all track and index points. For instance, you can rip a CD to a single file, then import the CD's extracted cue sheet while encoding to yield a single file representation of the entire CD. If your original CD is damaged, the cue sheet can be exported later in order to burn an exact copy.
方便 CD 存档： FLAC 有一个 " 提示表 " 元数据块，用来储存 CD 表内容、以及所有的追踪和索引点。例如，你可以将一张 CD 分裂成一个单独的文件，然后编码时导入 CD 提取的提示表，生成一个代表着整张 CD 的单独文件。如果你的原始的 CD 被损坏，提示表可以稍后导出，以便刻录出一个精确的副本。

Error resistant: Because of FLAC's framing, stream errors limit the damage to the frame in which the error occurred, typically a small fraction of a second worth of data. Contrast this with some other lossless codecs, in which a single error destroys the remainder of the stream.
抗差错性：因为 FLAC 的帧结构，流错误限制了对发生错误的帧的破坏，通常是每秒钟数据的一小部分。将这个和一些其他的无损编解码器进行比较，一个单一错误破坏剩下的流。

What FLAC is not:
Lossy. FLAC is intended for lossless compression only, as there are many good lossy formats already, such as Vorbis, MPC, and MP3 (see LAME for an excellent open-source implementation).
DRM. There is no intention to add any copy prevention methods. Of course, we can't stop someone from encrypting a FLAC stream in another container (e.g. the way Apple encrypts AAC in MP4 with FairPlay), that is the choice of the user.
FLAC 不是什么 :
有损 .FLAC 仅仅旨在无损压缩，因为已经有很多优质有损的格式，如： Vorbis, MPC, 和 MP3 ( 参考 LAME ，用于优秀的开源实现 ).
DRM. 无意去增加防止任何拷贝的方法。当然，我们不能阻止某些人在另一个容器中加密 FLAC 流（例如：苹果使用 FairPlay 的方式加密 MP4 中的 AAC ） , 这是用户的选择。