ffmpeg从内存读取文件

正常情况，ffmpeg直接从文件读取

AVFormatContext * _ctx = NULL;
avformat_open_input(&_ctx, _filePath, 0, 0);

我们也可以自定义从内存读取，这样，可以用于读取一些加密的视频文件

    int fill_iobuffer(void * opaque,uint8_t *buf, int bufsize){
        if(!feof(fp_open)){
            int true_size=fread(buf,1,bufsize,fp_open);
            return true_size;
        }else{
            return -1;
        }
    }

AVFormatContext * _ctx = NULL;
unsigned char* _iobuffer = (unsigned char*)av_malloc(32768);
AVIOContext* _avio = avio_alloc_context(_iobuffer , 32768 , 0 , NULL,fill_iobuffer,NULL,NULL);
_ctx->pb = _avio;

fp_open=fopen(_filename,"rb+");  

if ((ret = avformat_open_input(&_ctx, "nothing", 0, 0)) < 0) {
	printf( "Could not open input file.");
}