音视频常见问题

hints.ai_family = AF_UNSPEC;
hints.ai_socktype = SOCK_STREAM;
snprintf(portstr, sizeof(portstr), "%d", port);
if (s->listen)
    hints.ai_flags |= AI_PASSIVE;
int64_t start = av_gettime();
if (!hostname[0])
    ret = getaddrinfo(NULL, portstr, &hints, &ai);
else
    ret = getaddrinfo(hostname, portstr, &hints, &ai);
int64_t end = av_gettime();

struct sockaddr_in *ipv4 = (struct sockaddr_in *)ai->ai_addr;
char *ipAddress = (char *)malloc(INET_ADDRSTRLEN);
inet_ntop(AF_INET, &(ipv4->sin_addr), ipAddress, INET_ADDRSTRLEN);
ffmpeg_dns_success(uri,hostname,(end-start)/1000,ipAddress);
free(ipAddress);

av_dict_set(&ffp->format_opts, "headers", "Host: flv-meipai.8686c.com", 0);

AVDictionary *format_opts;

struct AVDictionary {
    int count;
    AVDictionaryEntry *elems;
};

typedef struct AVDictionaryEntry {
    char *key;
    char *value;
} AVDictionaryEntry;

err = avformat_open_input(&ic, is->filename, is->iformat, &ffp->format_opts);
avformat_open_input这个方法就是ffmpeg的打开流，并找到流媒体的头部信息的函数，具体可以参考另一篇文章Avformat_open_input函数的分析之--HTTP篇。传入以后，最终format_opts这个结构体会走到avio.c文件的ffurl_open_whitelist方法，并赋值给URLContext **puc结构体，代码如下:

    if (options &&
        (ret = av_opt_set_dict(*puc, options)) < 0)
        goto fail;
    if (options && (*puc)->prot->priv_data_class &&
        (ret = av_opt_set_dict((*puc)->priv_data, options)) < 0)
        goto fail;
// 然后最终会在http.c文件的发起http连接的函数http_connect方法中

char headers[HTTP_HEADERS_SIZE] = "";

if (!has_header(s->headers, "\r\nHost: "))
    len += av_strlcatf(headers + len, sizeof(headers) - len,
                        "Host: %s\r\n", hoststr);

if (s->headers)
        av_strlcpy(headers + len, s->headers, sizeof(headers) - len);