xdf 0.2.0

Read and write XDF (Extensible Data Format) recordings.

xdf

xdf reads and writes XDF (Extensible Data Format) recordings, the file format of LabRecorder and Lab Streaming Layer. It is pure Dart and runs on all platforms, including the web.

Clock synchronisation, jitter removal and effective sampling rates follow the algorithms and defaults of pyxdf. The results are tested against pyxdf 1.17.5 on the example files of xdf-modules (see test/fixtures).

To inspect an XDF file without writing code, it can be opened in LSL Viewer, which is built on this package. In the web app the file is read locally in the browser.

API documentation

Installation

dart pub add xdf

Usage

loadXdf reads a whole file into memory and corresponds to load_xdf in pyxdf:

import 'dart:io';

import 'package:xdf/xdf.dart';

void main() {
  final rec = loadXdf(File('session.xdf').readAsBytesSync());
  for (final s in rec.streams) {
    print('${s.info.name}: ${s.length} samples at ${s.effectiveRate} Hz');
  }
}

The package has four entry points:

Entry point	Purpose
loadXdf(bytes)	A whole file in memory, with synchronised clocks (robust fit, detection of clock resets), jitter removal and effective rates
XdfFile.open(ByteSource)	Files that are too large to load at once
XdfWriter	Writing a file as data arrives (headers, samples, clock offsets, boundaries, footers), for example to record LSL streams
readChunks, readSamples	The raw chunks of a file

Large files

XdfFile.open indexes a file in one pass and reads it on demand. For each regularly sampled stream it builds summary pyramids, from signal_core, so that overviews, zooming and filtered windows are fast. Markers and irregular streams are kept in memory. A stream without breaks receives exactly the time stamps that pyxdf assigns.