• accessor method accessor表示两个方法，一个叫做getter用于获取，另一个叫做setter用于设置。 getter形式为 - (type)name, setter形式为-(void)setName。 accessor method represents two method. one is getter and the other is setter. the method of getter defaults as ‘-(type)name and setter defaults as -(void)setName

• @property @property 生成 instance variable 和 accessor。 @property makes instance variable (ivar) and accessor

• @synthesize @synthesize与@property配对，提供将@proerty与成员变量绑定的功能，即指定@property的inistance variable为特定的成员变量。 synthesize prepairs @property.in @synthesize the ivar can bind a class member, @syntax property-name=ivar-name

• atomic atomic的意思是读和写是原子操作，但是线程安全要保证同时读写数据不会出错，所以atomic无法保证。本质就是在getter和setter加入一个锁，赋值或取值前锁定，结束后解除。nonatomic/atomic 原子操作，但不能保证线程安全，默认为atomic，常用为nonatomic。 nonatomic/atomic is atomic operation. this does not gurantee the safe-thread. default value is atomic.atomic means the reading and writing are atomic each,but the safe-thread requests reading and writing in the same time do not case the problem. the atomic add the lock in getter and setter.

• readonly/readwrite 读写或只读，本质就是生成getter和setter或者只生成getter readwrite makes the getter and setter and the readonly makes the only getter.

• weak/strong(assgin/retaine) copy weak/strong in ARC, weak means assgin in setter, strong means reference count draining in setter(complite manages automatic reference count). assgin/reatin in MRC are deprecated now. copy means using copy in setter. weak/strong作为ARC自动引用计数时代，weak本质是setter内直接赋值，strong本质是setter时增加引用计数（引用计数由编译器，编译时增加）（assign/retain 为MRC手动引用计数时代的标志，已经被淘汰） copy 表示setter中使用copy方式

• dotsyntax dotsyntax本质是转化为 getter 和 setter dotsyntax means sending getter or setter message.

2014-11-10

提取音频

ffmpeg -i input -vn output.mp3

-vn 不需要视频 no video

压缩

ffmpeg -i input -acodec copy -vcodec copy -s 800x600 output

-s scale 压缩后大小