函数 av_probe_input_format3 

pub unsafe extern "C" fn av_probe_input_format3(
    pd: *const AVProbeData,
    is_opened: c_int,
    score_ret: *mut c_int,
) -> *const AVInputFormat

Guess the file format.

@param is_opened Whether the file is already opened; determines whether demuxers with or without AVFMT_NOFILE are probed. @param score_ret The score of the best detection.