Technical Reference:BCI2000 File Format

A BCI2000 data file consists of a header and the actual raw brain signals. Its associated file name extension is .dat. The header consists of a definition of all system parameters and states. Thus, parameter values cannot change within a [Run], which in turn corresponds to a single data file.

Header

The header of a data file consists of lines of ASCII characters, separated by a carriage return/line feed (CRLF) control character sequence typically present in DOS/Windows text files. Its total length is given by the HeaderLen field in the first line. The header contains meta information, state (event) definitions, and parameters.

Meta Information

The fields in the first line specify meta information required to access the binary data that follows the header.

Since version 1.1, the first line begins with a \textit{BCI2000V} field containing a floating point version number, and ends with a DataFormat field describing the format of the binary data as int16, int32, or float32. A missing \textit{BCI2000V} field indicates a file format version of 1.0, and a DataFormat of int16.

The number of bytes in the state vector is determined by the sum of the lengths (defined in bits) for all states, rounded up to the next byte (which equals the value of StateVectorLength in both the first line and, since StateVectorLength is also a system-wide parameter, in one of the lines in the [Parameter Definition] section). Thus, the first line contains all information required to read the binary information contained in the data file.

State Definitions

State definitions are preceded with a line [ State Vector Definition ], and given in the general [State Definition] format. In the context of the file header, the state definitions' value fields are redundant since they match the values associated with the first sample in the data file.

Parameter Definitions

Parameter definitions are preceded with a line [ Parameter Definition ], and follow the general [Parameter Definition] format. They represent the respective parameters' values at the beginning of the recording.

Summary

BCI2000V= 1.1 HeaderLen= l SourceCh= m StateVectorLength= k DataFormat= f CRLF
[ State Vector Definition ] CRLF
Name1 Length1 Value1 ByteLocation1 BitLocation1 CRLF
Name2 Length2 Value2 ByteLocation2 BitLocation2 CRLF
Name3 Length3 Value3 ByteLocation3 BitLocation3 CRLF
...
[ Parameter Definition ] CRLF
Section1 DataType1 Name1= Value1 DefaultValue1 LowRange1 HighRange1 // Comment CRLF
Section2 DataType2 Name2= Value2 DefaultValue2 LowRange2 HighRange2 // Comment CRLF
Section3 DataType3 Name3= Value3 DefaultValue3 LowRange3 HighRange3 // Comment CRLF
...
CRLF

Binary Data

The binary data directly follows the last CRLF. For each sample, data values for all channels are stored, followed by StateVectorLength bytes for the state vector. Data samples are always stored in little endian byte ordering. Their format depends on the DataFormat field:

DataFormat field	data type
int16	2-byte signed integer
int32	4-byte signed integer
float32	4-byte floating point (IEEE 754)

From the total file size, and the information present in the header's first line, the number of samples in a data file may be calculated as follows:

Software Components

• For writing, information about the BCI2000 data file format is encapsulated into the shared/fileio/dat/BCIDatFileWriter component.
• For reading, information about the BCI2000 data file format is encapsulated into shared/fileio/dat/BCIDatFileReader.
• A Matlab mex file to read BCI2000 data files is provided at Tools/mex/load_bcidat. This mex file uses the BCIDatFileReader component.