The .usb file format is not documented and may change as we add features to the 1480A USB Protocol Analyzer. Because of this, we currently do not offer an SDK to decode the data. The .usb file stream is also encoded to minimize its size. Before being displayed in the 1480A software the .usb file stream is converted to a .atm file which contains absolutely timestamped messages from the hardware. These timestamped messages are then displayed in the message view. The interesting things in the message view are the data packets (comes after RxCmds with RxActive bit set), J and K line state (shown as DATA0 and DATA1 in the 'decoded data' column of the RxActive items). There are also 'Events' shown in the message view. These are internal state machine transitions in the 1480A that tell the 1480A software that devices have connected, disconnected etc.
For the low-level details regarding the information picked up from the USB, please see the
NXP transceiver datasheet.