函数 av_packet_make_writable 

pub unsafe extern "C" fn av_packet_make_writable(
    pkt: *mut AVPacket,
) -> c_int

Create a writable reference for the data described by a given packet, avoiding data copy if possible.

@param pkt Packet whose data should be made writable.

@return 0 on success, a negative AVERROR on failure. On failure, the packet is unchanged.