函数 av_probe_input_format 

pub unsafe extern "C" fn av_probe_input_format(
    pd: *const AVProbeData,
    is_opened: c_int,
) -> *const AVInputFormat

Guess the file format.

@param pd data to be probed @param is_opened Whether the file is already opened; determines whether demuxers with or without AVFMT_NOFILE are probed.