AVFormatContext.start_time_realtime

Start time of the stream in real world time, in microseconds since the Unix epoch (00:00 1st January 1970). That is, pts=0 in the stream was captured at this real world time. - muxing: Set by the caller before avformat_write_header(). If set to either 0 or AV_NOPTS_VALUE, then the current wall-time will be used. - demuxing: Set by libavformat. AV_NOPTS_VALUE if unknown. Note that the value may become known after some number of frames have been received.

struct AVFormatContext
int64_t start_time_realtime;

Meta