EDF(+): Video

European Data Format

Specs

Full specification of Video files for EDF

Sleep and EEG investigations are increasingly accompanied by video recordings. Archival and exchange of the video files seems no problem because video replay software is widely and freely available. However, the time synchronization to the PSG or EEG recording is always handled by proprietary methods. Therefore the time synchronization is lost if different manufacturers are involved, for instance in multi-center studies or when replacing equipment. This page provides a solution by simply coding the video start-date and -time into the video filename. This is the only action required to give (y)our video data a much longer and more prosperous life. Polyman has a video demo on board, based on this filename convention.

The specification

In order to use this video specification, all EDF(+) filenames should start with the patient identification. For instance the PSG of patient NL-012348168 would be in file:
        NL_012348168_PSG.edf
Note that EDF(+) files have their start-date and -time specified in the file. Video files have no such specification.

Video filenames of the same patient must start with the same patient identification, followed by the start-date and -time of the video, as follows:
        NL_012348168_03-MAY-2013_14h45m49.013s_Video.ogv
in which case the video apparently starts on May 3, 2013 at 0.013 seconds after 14:45:49hr. To be more precise, the patient identification is followed by an underscore (_), followed by the video startdate DD-MMM-YYYY, followed by an underscore, followed by the starttime HHhMMmSS.XXXXs. The startdate days, DD, are 01, 02, 03, … 30 or 31. The months, MMM, are JAN, FEB, MAR, APR, MAY, JUN, JUL, AUG, SEP, OCT, NOV or DEC. The years, YYYY, obviously are 2013, 2014 and so on. The starttime is based on the 24h clock with HH ranging from 00 till 23, so midnight is coded as 00h00m00s. The decimal fraction of a second (noted here by .XXXX) can have any lenght and can also be omitted (for example in 06h37m12s). The addition _Video is not obligatory and neither do we standardize any video format such as ogv. So, a perfectly OK video filename would also be:
        NL_012348168_03-MAY-2013_14h45m49.013s.mpeg

Note that the EDF(+) filename can specify its start-date and -time in a similar way, for instance in order to more easily organize recordings from the same patient, but this is not obligatory.

Implementation

Using this convention, we have integrated the Microsoft Media player in our Polyman EDF reviewer in such a way that video and EDF remain synchronized during replay of either one. Because Polyman is freely downloadable from the EDF website, the only action needed to make this work in other labs is to rename the EDF(+) and video files according to this specification. In order to make it work with other review software, that software also would need to adopt this filename convention.