FFMPEG类库接收流媒体的方法出现丢包情况(设置参数)

使用ffmpeg类库进行开发的时候，打开流媒体（或本地文件）的函数是avformat_open_input()。

其中打开网络流的话，前面要加上函数avformat_network_init()。

一般情况下，只要传入流媒体的url就可以了。但是在打开某些流媒体的时候，可能需要附加一些参数。

如果直接进行打开是不会成功的，我们可以使用ffplay做一下实验：

ffplay rtsp://mms.cnr.cn/cnr003?MzE5MTg0IzEjIzI5NjgwOQ==  

会出现错误：

Invalid data found when processing input

这时候我们需要指定其传输方式为TCP，需要将命令改为如下形式：

ffplay -rtsp_transport tcp rtsp://mms.cnr.cn/cnr003?MzE5MTg0IzEjIzI5NjgwOQ==  

附加了参数以后，发现就可以正常播放了。

此外还可以附加一些参数，比如

ffplay -rtsp_transport tcp -max_delay 5000000 rtsp://mms.cnr.cn/cnr003?MzE5MTg0IzEjIzI5NjgwOQ==  

如下ffmpeg代码进行收流器时，

in_filename = "rtsp://admin:[email protected]/ rtsp -i -rtsp_transport tcp -fix_sub_duration  -async -1 -use_wallclock_as_timestamps";
	//in_filename  = "rtp://233.233.233.233:6666";
	//out_filename = "receive.ts";
	//out_filename = "receive.mkv";
	out_filename = "ccd_receive.mkv";

	av_register_all();
	//Network
	avformat_network_init();
	//Input
	if ((ret = avformat_open_input(&ifmt_ctx, in_filename, 0, &avdic)) < 0) {
		printf("Could not open input file.");
		goto end;
	}

参数日志信息如下：

提示丢包了。

看一下avformat_open_input()的定义：

/**
 * Open an input stream and read the header. The codecs are not opened.
 * The stream must be closed with avformat_close_input().
 *
 * @param ps Pointer to user-supplied AVFormatContext (allocated by avformat_alloc_context).
 *           May be a pointer to NULL, in which case an AVFormatContext is allocated by this
 *           function and written into ps.
 *           Note that a user-supplied AVFormatContext will be freed on failure.
 * @param url URL of the stream to open.
 * @param fmt If non-NULL, this parameter forces a specific input format.
 *            Otherwise the format is autodetected.
 * @param options  A dictionary filled with AVFormatContext and demuxer-private options.
 *                 On return this parameter will be destroyed and replaced with a dict containing
 *                 options that were not found. May be NULL.
 *
 * @return 0 on success, a negative AVERROR on failure.
 *
 * @note If you want to use custom IO, preallocate the format context and set its pb field.
 */
int avformat_open_input(AVFormatContext **ps, const char *url, AVInputFormat *fmt, AVDictionary **options);

可以看出avformat_open_input()的第4个参数是一个AVDictionary类型的参数。这个参数就是传入的附加参数。

设置AVDictionary的时候会用到av_dict_set()。

修改程序如下，设置AVDictionary参数如下：

AVDictionary *avdic = NULL;
	char option_key[] = "rtsp_transport";
	char option_value[] = "tcp";
	av_dict_set(&avdic, option_key, option_value, 0);
	char option_key2[] = "max_delay";
	char option_value2[] = "5000000";
	av_dict_set(&avdic, option_key2, option_value2, 0);

	av_register_all();
	//Network
	avformat_network_init();
	//Input
	if ((ret = avformat_open_input(&ifmt_ctx, in_filename, 0, &avdic)) < 0) {
		printf("Could not open input file.");
		goto end;
	}

最后程序正常接收数据包