[FieldTrip] Issue with Loading OPM FIF Files (fiff_dir_tree_find Failure)

[Christoph Pfeiffer]

Hi Daeun,

What kind of OPM system are you using?

We've seen an issue with corrupted files a while ago with our Fieldline system when we ran out of disk space during a recording. The header was updated but the data not added resulting in an unreadable file. They have since added a fix that gives you a warning if you get too close to limit of your disc.

Best,
Christoph
________________________________
From: fieldtrip <fieldtrip-bounces at science.ru.nl> on behalf of Daeun Gwon via fieldtrip <fieldtrip at science.ru.nl>
Sent: Wednesday, November 26, 2025 5:45
To: fieldtrip at science.ru.nl <fieldtrip at science.ru.nl>
Cc: Daeun Gwon <danigwon at gmail.com>
Subject: [FieldTrip] Issue with Loading OPM FIF Files (fiff_dir_tree_find Failure)


I hope you are doing well. I am writing to report an issue related to loading our OPM data (FIF format) using both MATLAB (FieldTrip) and Python (MNE).

Issue Summary

  *   Some FIF files recorded in the same experiment session fail to load properly.

  *   The end portion of the data appears truncated when loaded.

  *   This occurs identically in both MATLAB and Python, while certain PCs load all files without any issues. This suggests that the data files themselves are not corrupted.

Technical Details

  *   In MATLAB, we confirmed that the problem occurs inside the fiff_setup_read_raw function, specifically at line 79 where fiff_dir_tree_find is called.

  *   For files that fail to load, the raw.dir structure contains corrupted values.

     *   Normally, values such as kind and type are consistent integers (e.g., kind = 300, type = 4).

     *   In problematic files, the last entry contains abnormal values (e.g., kind = -113471426, type = -1.103131550000000e+09).

  *   The implementation of fiff_dir_tree_find does not show abnormalities, making debugging difficult.

  *   We are using the latest FieldTrip version cloned from GitHub and the fieldtrp Web's download

If you could provide any guidance or suggestions for further debugging, or if you are aware of similar cases, your help would be greatly appreciated.

Thank you very much in advance.

Best regards,
Daeun Gwon

--
Daeun Gwon (Ph.D.)
Dept. of Computer Science and Electrical Engineering
Handong Global University (HGU), South Korea
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