AAC-LC 是什么格式？和 AAC 有什么区别？

AAC（Advanced Audio Coding） 编码9种规格：

MPEG-2 AAC LC低复杂度规格（Low Complexity）

MPEG-2 AAC Main主规格

MPEG-2 AAC SSR可变采样率规格（Scaleable Sample Rate）

MPEG-4 AAC LC低复杂改败度规格（Low Complexity）

MPEG-4 AAC Main主规格

MPEG-4 AAC SSR可变采样率规格（Scaleable Sample Rate）

MPEG-4 AAC LTP长时期预测规格（Long Term Predicition）

MPEG-4 AAC LD低延迟规格（Low Delay）

MPEG-4 AAC HE高效率规格（High Efficiency）

上述的规格中，主规格（Main）包含了除增益控制之外的全部功能，其音质最好，而低复杂度规格（LC）则是比较简单，没有了增益控制，但提高了编码效率，故使用（LC）是为了降低文件体积，有一定音质损失。

.M4A 是为了区别纯音频MP4文件和包含视频的MP4文件而由苹核租颤果（Apple）公司使用的扩展名，Apple iTunes对纯音频MP4文件采用了".M4A"命名。M4A的本质和音频MP4相同，故音频MP4文件亦可直接更改扩展名为M4A。文件 .M4A 只是改了后缀而已，还是 AAC 的编码，只要能解码 AAC 就可以播放 .M4A 文件，但有一种例外是苹果（Apple）的另一种音频编码 Apple Lossless 也使用.M4A 作为文件后缀，这种编码应该是只有苹果（Apple）产品才支持。

在我实际测试中，Sony 的 Walkman 确实是不支持 Apple Lossless 编码的 .M4A 音频，但是 AAC 编码的 .M4A 没型禅有任何问题（码率范围 128kbps～320kbps）。

Letter of credit

Letter of Credit (Letter of Credit, L / C), is the issuing bank should be the applicant's request in accordance with its instructions to the third contained a certain amount of prescribing, in a certain period of time with the required payment documentation file a written guarantee. Letter of credit is the most important international trade, the most common method of payment.

In international trade activities, both parties may distrust, fear advances buyer, the seller is not required under the contract deliveryseller also worry about delivery or shipping documents submitted to the buyer does not pay. Therefore, the two banks as buyers and sellers need a guarantor, on behalf of receiving pay bills, bank credit instead of commercial credit. Bank activities in this tool is used in the letter of credit.

Shows that bank credit is a conditional guarantee of payment certificate, the international trade in the common method of settlement. In accordance with the general provisions of this settlement, the buyer first deposit money banks, by a bank letter of credit, notify the depositary bank remote seller to convey to the vendor, contracts and letters of credit provided by the terms of shipping, banking on behalf of the buyer's payment.

Glossary: Credit English as: letter of credit. Abbreviated as: l / c, or LOC.

① In the bond issuance process, a commitment issued by a bank guarantee when the debtor to the debt service schedule. If the bond issuer is unable to fulfill the repayment obligations, the bank will issue letters of credit to fulfill the repayment obligations.

② in international trade, importers exporters bank to pay the bank guarantee issued documents, and promised that after the goods arrive at the importer or exporter of goods, to the Export Bank to issue payments.

Contents:

(1) description of the letter of credit itself. As its type, nature, duration and place of maturity.

(2) the requirements of the goods. Described under the contract.

(3) transportation requirements.

(4) documentation requirements, that is, goods receipts, transport documents, insurance documents and other relevant documents.

(5) special requirements.

(6) The issuing bank drafts to beneficiaries and holders of the responsibility to ensure payment terms of the motion.

(7) to permit the majority of all foreign notation: "Unless otherwise specified, the International Chamber of Commerce" Uniform Customs and Practice for Documentary Credits, "the International Chamber of Commerce Publication No. 600 (" ucp600 ") process."

(8) The provisions of the inter-bank wire transfer claims (t / t reimbursement clause).

Main features of letters of credit have three characteristics: First, not dependent on credit sales contract, a single bank in the trial, stressed that the basis of trade credit and formal separation of the written certificationsecond letter of credit is a payment voucher, not to subject the goods. As long as the documents in line with the issuing bank should be unconditional paymentthird letter of credit is a bank credit, which is the bank of a security document.

46a.1.由受益人出具并签字的商业发票一式4份，其中正本须由中国贸易促进委员会（贸促会）的签章证明。2.1整套清洁已装船海运提单正本 1副本，副本要背书：JORDAN ISLAMIC BANK,CHOWING.1)运费到付（目的地付）2）Notify party(被通知人)同开证人.3.Packing list， 必须列明每箱所装货物的详细内容。（没列明所需的份数，一正 1副好了。）4.原产地证（由贸促会开出，注明制造商的名称并声明货物原产自中国---当然了。）5. 由船公司或其代理或船东开具的声明该船符合ISM标准的声吵拿侍明一份。47/A1.所有运输单据注明的发货人必须为该信用证的受益人，其它升吵任何第三方都不接受。2.所有文件必须注明出具日期，交货/开船日期不可早于开证日期。3.不可提前预支/议付，即使提供担保也不成。4.所有文件必须注明L/C号码。5.提单必须显示所乘载的船不会按约旦法律法规在约旦港口被拒，或由船公司出具的此类声明也可。6.提单上必须列明该船公司在约旦的代理公司的电话，名称，地址。7.发票及其它文件应该敏拍声明the goods required........standards.8.所有文件需要以英文出具。

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