知识总结

(1)av_rescale_q(int a,R b,R q)     等价    a * b * (1/q)

 

(2)mp3                spf = 576: 1152

(3)url_fseek()

{

     s->seek();

    s->buf_ptr = s->buffer;          //当前地址指向缓冲区开始处

}

get_buffer

{

            if(size > s->buffer_size && !s->update_checksum)            //需要的数据量大于缓冲区大小就直接从源读取
            {
                if(s->read_packet)
                    len = s->read_packet(s->opaque, buf, size);
                if (len <= 0)
                {
                    /* do not modify buffer if EOF reached so that a seek back can
                    be done without rereading data */
                    s->eof_reached = 1;
                    if(len<0)
                        s->error= len;
                    break;
                }
                else
                {
                    s->pos += len;
                    size -= len;
                    buf += len;
                    s->buf_ptr = s->buffer;                              //当前地址和结尾地址都指向缓冲区开始处
                    s->buf_end = s->buffer/* + len*/;
                }
            }

}