HCCAP is a custom format, specifically developed for oclHashcat-plus.

The data itself does not differ from usual tcpdump format. In fact, it's absolutely the same. It is just rearranged a bit.

typedef struct
{
  char          essid[36];

  unsigned char mac1[6];
  unsigned char mac2[6];
  unsigned char nonce1[32];
  unsigned char nonce2[32];

  unsigned char eapol[256];
  int           eapol_size;

  int           keyver;
  unsigned char keymic[16];

} hccap_t;