If you need a primer on 'How to configure PTP' on Arista click here. If you understand Arista's implementation of PTP then wait no further and read the rest of the blogtorial on how to decode them from a RAW packet capture.
Key frames DATA is 46bytes and is broken down as follows. What is in bold is important for calculating UTC time of a given packet.
8Bytes - ASIC Ticks
8Bytes - UTC in ns
8Bytes - LAST SYNC
8Bytes - KEY TS
8Bytes - EGRESS Interface DROPS
2Bytes - User defined DEVICE ID
2Bytes - Egress interface of the keyframe
1Byte - FCS TYPE
1Byte - RESERVED