/**
* 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 filename Name 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 *filename, AVInputFormat *fmt, AVDictionary **options);
该函数用于打开一个输入流并读取它的头部。
参数说明:
AVFormatContext **ps: 格式化的上下文。要注意,如果传入的是一个AVFormatContext*的指针,则该空间须自己手动清理,若传入的指针为空,则FFmpeg会内部自己创建。
const char *filename: 要打开的流的文件名,传入的地址。支持http,RTSP,以及普通的本地文件。地址最终会存入到AVFormatContext结构体当中。
AVInputFormat *fmt: 强制指定输入的封装格式。一般传NULL,由FFmpeg自行探测。
AVDictionary **options: 其它参数设置。它是一个字典,用于参数传递,不传则写NULL。参见:libavformat/options_table.h,其中包含了它支持的参数设置。