Some forms of data, particularly those that are generated by proprietary hardware and software, are difficult to reformat, and in those cases the data may need to be uploaded as-is to the repository. In many cases, however, data can be rendered in tabular format, in which case CSV (comma-separated value) format is recommended as it is the most accessible and interoperable format for tabular data.
For qualitative data, RTF (rich-text format) offers the best balance between simplicity and formatting, while XML is a good choice for those who have complicatedly-formatted data.
For further reading, the UK Data archive has a guidance document which includes the optimal formats for various kinds of data, including audio-visual data formats.
