directshow ALLOCATOR_PROPERTIES结构解释？
typedef struct _AllocatorProperties {
long cBuffers;
long cbBuffer;
long cbAlign;
long cbPrefix;
} ALLOCATOR_PROPERTIES;
谁能具体说明一下long cbAlign; long cbPrefix;的意义？
[解决办法]
cbAlign
Alignment of the buffer; buffer start will be aligned on a multiple of this value.
cbPrefix
Each buffer is preceded by a prefix of this many bytes.
sdk上说的挺清楚啊，cbAlign就是buffer地址要求多少byte对齐。
cbPrefix 就是每块buffer前面有多少前缀空间。
需要注意的是下面：
Since the buffer pointer returned by IMediaSample::GetPointer points to the area immediately following the prefix, the cbPrefix address (the value returned by IMediaSample::GetPointer minus cbPrefix) should be aligned on an address that is a multiple of cbAlign bytes.
[解决办法]
楼上说的对
没有特殊要求的话，一般cbAlign就是1，cbPrefix是0
[解决办法]
如果下游filter也是你自己写的话，就可以用prefix，你可以通过sample buffer将参数传递下去，下游filter计算好buffer地址就可以。
如buffer中前10bytes存储的是数据，之后才是真正的sample data，那么下游filter就要知道这块buffer的分布情况。
