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Xtc to Hdf5 translation is performed by a psana module.  Previously translation was performed by an external tool: o2o-translate.  Documentation on O2OTranslator, which discusses some history with regards to selecting hdf5 for a scientific data format for general use can be found

Translator
User Interface to Translator

Automatic translation of xtc to hdf5 is managed by the Interface Controlller.

A discussion of the input and hdf5 output formats format for translator can be found here:

Event data format - the input format
The contents of HDF5 files - the output format. It is worth spending some time with this document, key points:

• Datasets need not be aligned.  That is the 5th image in a detector dataset may come from a different datagram (or event) than the 5th record in a gas detector dataset. That is there time's may not be the same.
• One should use the _mask datasets to identify valid data. A _mask dataset record is 1 when the corresponding record of the data dataset if valid, 0 if it is not. A blank (all zeros) is generated in the data dataset record when it is not valid.
• Where to find your data:
  
  • The hdf5 group hierarchy has the following levels: run, calib cycle. type, source  - regular event data is organized into datasets that live at the source level, epics has its own place, and configuration data (that usually arrives once) as its own place as well.
• Aligning datasets - when correlating different datasets, one must use each source level 'time' dataset to check which events are present.

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