函数 av_crc 

pub unsafe extern "C" fn av_crc(
    ctx: *const AVCRC,
    crc: u32,
    buffer: *const u8,
    length: usize,
) -> u32

Calculate the CRC of a block. @param ctx initialized AVCRC array (see av_crc_init()) @param crc CRC of previous blocks if any or initial value for CRC @param buffer buffer whose CRC to calculate @param length length of the buffer @return CRC updated with the data from the given block

@see av_crc_init() “le” parameter