Read MEF 3.0 in MATLAB

addpath('<somewhere>/mef3io-matlab')   % the unzipped release bundle
r = mef3io.Reader('recording.mefd');
r.channels                             % channel names
x = r.read('Fp1');                     % whole channel, double column, gaps are NaN
info = r.info('Fp1');
fs = info.sampling_frequency;

Get the mef3io-matlab-vX.Y.Z.zip bundle from a GitHub release; on the supported platforms it works without compiling anything. x holds the values in physical units (info.units_description, for example uV), one per sample period from the channel's first sample to its last.

A time window

MEF 3.0 times are microseconds since 1970-01-01 UTC ("uUTC"). Ask for a window [t0, t1); only the data needed for it is read from disk, so this is fast even on a recording of many gigabytes.

firstMinute = r.read('Fp1', info.start_time, info.start_time + int64(60e6));

when = datetime(2024, 3, 5, 9, 30, 0, 'TimeZone', 'UTC');
t0 = int64(posixtime(when) * 1e6);
tenSeconds = r.read('Fp1', t0, t0 + int64(10e6));

A window returns round((t1 - t0) * fs / 1e6) samples. Sample i (counting from 1) is at t0 + (i - 1) * 1e6 / fs.

Gaps are NaN

Where the recording has no data (an electrode was off, acquisition paused), read returns NaN at those positions instead of shifting later samples earlier. Times stay correct.

missing = isnan(x);
fprintf('%.1f%% of the span has no data\n', 100 * mean(missing));
clean = x(~missing);                   % only the recorded samples
segs = r.segments('Fp1');              % where the data is, without reading it

See Long recordings with gaps for finding gaps.

Annotations

anns = r.records();                    % session level: type, time (uUTC), text
anns = r.records('Fp1');               % one channel's annotations

Encrypted sessions and archives

r = mef3io.Reader('recording.mefd', 'your password');
r = mef3io.Reader('recording.mefd.tar');   % single-file archive, read in place

The level-2 password opens everything; the level-1 password reads the signals but not the subject fields or the annotations (what encryption protects).

More

The MATLAB guide covers the rest: stored integer values (readRaw), lenient opening of damaged sessions, writing and archives.