轉(zhuǎn)載：https://www.jianshu.com/p/3c95b0471d3a

1 // 不要用第四個(gè)參數(shù)傳自定的數(shù)據(jù)，當(dāng)av_read_frame的時(shí)候會(huì)出問題，無限循環(huán)
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開頭會(huì)讀取部分?jǐn)?shù)據(jù)探測(cè)流的信息,不會(huì)全部讀取，除非設(shè)置的緩存過大
6 av_read_frame會(huì)在讀幀的時(shí)候調(diào)用avio_alloc_context中的read_packet方法取流數(shù)據(jù)，每隔avio_ctx_buffer_size調(diào)用一次，直至讀完
7 */

 1 /*正確方式*/
 2 struct buffer_data
 3 {
 4     uint8_t *ptr; /* 文件中對(duì)應(yīng)位置指針 */
 5     size_t size;  ///< size left in the buffer /* 文件當(dāng)前指針到末尾 */
 6 };
 7 
 8 // 重點(diǎn)，自定的buffer數(shù)據(jù)要在外面這里定義
 9 struct buffer_data bd = {0};
10 
11 //用來將內(nèi)存buffer的數(shù)據(jù)拷貝到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 /* 打開前端傳來的視頻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     /* 讀內(nèi)存數(shù)據(jù) */
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     /* 打開內(nèi)存緩存文件, 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 }

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