2014 10 19
ffmpeg 1.0 filter模塊AVFilterPad結構的權限屬性min_perms/rej_perms分析：
1.註釋翻譯
輸入pad:
輸入buffer最小權限要求.
如果buffer權限不夠，則filter系統自動將其copy到一個能提供相應權限的新buffer
輸出pad:
將要輸出的buffer的保護權限.
任何想要在link上輸出的buffer必須具備這些權限.
這些使用assert來檢查的。這可以優化buffer分配。
/**
* Input pads:
* Minimum required permissions on incoming buffers. Any buffer with
* insufficient permissions will be automatically copied by the filter
* system to a new buffer which provides the needed access permissions.
*
* Output pads:
* Guaranteed permissions on outgoing buffers. Any buffer pushed on the
* link must have at least these permissions; this fact is checked by
* asserts. It can be used to optimize buffer allocation.
*/
int min_perms;
輸入pad:如果輸入buffer有這些權限，則輸入pad拒絕。如果buffer有這些拒絕權限，
則filter系統自動將其copy到一個沒有這些權限的新buffer。
輸出pad:輸出buffer自動刪除這些拒絕權限。這可以用來優化buffer分配。
/**
* Input pads:
* Permissions which are not accepted on incoming buffers. Any buffer
* which has any of these permissions set will be automatically copied
* by the filter system to a new buffer which does not have those
* permissions. This can be used to easily disallow buffers with
* AV_PERM_REUSE.
*
* Output pads:
* Permissions which are automatically removed on outgoing buffers. It
* can be used to optimize buffer allocation.
*/
int rej_perms;
2.實現
在video.c文件ff_start_frame函數裏實現：
min_perms[輸出]：//任何想要在link上輸出的buffer必須具備這些權限
av_assert1((picref->perms & src->min_perms) == src->min_perms);
rej_perms[輸出]：//輸出buffer自動刪除這些拒絕權限
picref->perms &= ~ src->rej_perms;
min_perms[輸入]/rej_perms[輸入]：
//min_perms:輸入buffer最小權限要求. 如果buffer權限不夠，則filter系統自動將其copy到一個能提供相應權限的新buffer
//min_perms:如果輸入buffer有這些權限，則輸入pad拒絕。如果buffer有這些拒絕權限，則filter系統自動將其copy到一個沒有這些權限的新buffer
if ((dst->min_perms & perms) != dst->min_perms || dst->rej_perms & perms) {