ffmpeg基础 -- avio_alloc_context 读内存

转载：https://www.jianshu.com/p/3c95b0471d3a

1 // 不要用第四个参数传自定的数据，当av_read_frame的时候会出问题，无限循环
2 avio_ctx = avio_alloc_context(avio_ctx_buffer, avio_ctx_buffer_size, 0, NULL, read_packet, NULL, NULL);
3 
4 /* 
5 avio_alloc_context开头会读取部分数据探测流的信息,不会全部读取，除非设置的缓存过大
6 av_read_frame会在读帧的时候调用avio_alloc_context中的read_packet方法取流数据，每隔avio_ctx_buffer_size调用一次，直至读完
7 */

 1 /*正确方式*/
 2 struct buffer_data
 3 {
 4     uint8_t *ptr; /* 文件中对应位置指针 */
 5     size_t size;  ///< size left in the buffer /* 文件当前指针到末尾 */
 6 };
 7 
 8 // 重点，自定的buffer数据要在外面这里定义
 9 struct buffer_data bd = {0};
10 
11 //用来将内存buffer的数据拷贝到buf
12 int read_packet(void *opaque, uint8_t *buf, int buf_size)
13 {
14 
15     buf_size = FFMIN(buf_size, bd.size);
16 
17     if (!buf_size)
18         return AVERROR_EOF;
19     printf("ptr:%p size:%zu bz%zu
", bd.ptr, bd.size, buf_size);
20 
21     /* copy internal buffer data to buf */
22     memcpy(buf, bd.ptr, buf_size);
23     bd.ptr += buf_size;
24     bd.size -= buf_size;
25 
26     return buf_size;
27 }
28 
29 /* 打开前端传来的视频buffer */
30 int open_input_buffer(uint8_t *buf, int len)
31 {
32     unsigned char *avio_ctx_buffer = NULL;
33     size_t avio_ctx_buffer_size = 32768;
34     
35     AVInputFormat* in_fmt = av_find_input_format("h265");
36 
37     bd.ptr = buf;  /* will be grown as needed by the realloc above */
38     bd.size = len; /* no data at this point */
39 
40     fmt_ctx = avformat_alloc_context();
41 
42     avio_ctx_buffer = (unsigned char *)av_malloc(avio_ctx_buffer_size);
43     
44     /* 读内存数据 */
45     avio_ctx = avio_alloc_context(avio_ctx_buffer, avio_ctx_buffer_size, 0, NULL, read_packet, NULL, NULL);
46 
47     fmt_ctx->pb = avio_ctx;
48     fmt_ctx->flags = AVFMT_FLAG_CUSTOM_IO;
49 
50     /* 打开内存缓存文件, and allocate format context */
51     if (avformat_open_input(&fmt_ctx, "", in_fmt, NULL) < 0)
52     {
53         fprintf(stderr, "Could not open input
");
54         return -1;
55     }
56     return 0;
57 }