2011-10-10 0:22:22-优快云博客

本文链接：https://blog.youkuaiyun.com/cstk502/article/details/6857576

本文详细介绍了AVCodec库的初始化过程以及如何注册不同类型的协议，包括MUXDEMUX、PROTOCOL等，对于理解多媒体文件处理的基础至关重要。

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2011-10-10 0:22:22

4. 上面调用了avcodec_init函数:

void avcodec_init(void)
{
   static int initialized = 0;

   if (initialized != 0)
   return;
   initialized = 1;

   dsputil_static_init ();
}

av_cold void dsputil_static_init(void)
{
   int i;

   for(i=0;i<256;i++) ff_cropTbl[i + MAX_NEG_CROP] = i;
   for(i=0;i<MAX_NEG_CROP;i++) {
   ff_cropTbl[i] = 0;
   ff_cropTbl[i + MAX_NEG_CROP + 256] = 255;
   }

   for(i=0;i<512;i++) {
   ff_squareTbl[i] = (i - 256) * (i - 256);
   }

   for(i=0; i<64; i++) inv_zigzag_direct16[ff_zigzag_direct[i]]= i+1;
}

   REGISTER_MUXDEMUX (H264, h264);

   // 注册文件协议
   REGISTER_PROTOCOL (FILE, file);

注册mux和demux

#define REGISTER_MUXER(X,x) { \
   extern AVOutputFormat x##_muxer; \
   if(CONFIG_##X##_MUXER) av_register_output_format(&x##_muxer); }

#define REGISTER_DEMUXER(X,x) { \
   extern AVInputFormat x##_demuxer; \
   if(CONFIG_##X##_DEMUXER) av_register_input_format(&x##_demuxer); }

#define REGISTER_MUXDEMUX(X,x) REGISTER_MUXER(X,x); REGISTER_DEMUXER(X,x)

#define REGISTER_PROTOCOL(X,x) { \
   extern URLProtocol x##_protocol; \
   if(CONFIG_##X##_PROTOCOL) av_register_protocol(&x##_protocol); }





URL协议结构:
typedef struct URLProtocol {
   const char *name;
   int (*url_open)(URLContext *h, const char *url, int flags);
   int (*url_read)(URLContext *h, unsigned char *buf, int size);
   int (*url_write)(URLContext *h, unsigned char *buf, int size);
   int64_t (*url_seek)(URLContext *h, int64_t pos, int whence);
   int (*url_close)(URLContext *h);
   struct URLProtocol *next;
   int (*url_read_pause)(URLContext *h, int pause);
   int64_t (*url_read_seek)(URLContext *h, int stream_index,
   int64_t timestamp, int flags);
   int (*url_get_file_handle)(URLContext *h);
} URLProtocol;