Historical data format is the same as provided by real-time FTX US WebSocket API with addition of local timestamps. If you'd like to work with normalized data format instead (same format for each exchange) see downloadable CSV files or official client libs that can perform data normalization client-side.
Tardis-machine is a locally runnable server that exposes API allowing efficiently requesting historical market data for whole time periods in contrast to HTTP API that provides data only in minute by minute slices.
orderbookGrouped - available since 2020-07-21
Asorderbook channel provides data only about the orderbook's best 100 orders on either side, grouped orderbooks channel supplies orderbook data with grouped (collapsed) prices allowing retrieving lower-granularity, higher-depth information about the orderbook.
We set grouping param to currency pairs' priceIncrement value multiplied by 10.