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== 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);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;
}