My research assistant is coding data for me - adding glosses to time-aligned signs. When she sends me her eaf file, I open it and I see the same gloss aligned slightly differently to the video, only by a frame or so but still. Why is this? It’s causing a huge problem. Is there any possible explanation for it? She has a PC and I have a Mac. Is this the problem?
Hello,
If the glosses are on a dependent tier of the tier containing the time-aligned signs, they should match the alignment of the signs. But maybe the signs themselves are already aligned differently on macOS and Windows and is that the problem.
This sometimes happens if the media player frameworks of the two platforms interpret the encoding of the video differently, e.g. in case of mp4 video files encoded with B-Frames (see this media encoding guide).
But maybe I’m wrong and this is not the issue here.
-Han
Hi Han,
Thank you for your quick response. I hope you don’t mind but I want to explain the issue more clearly here. When I open up the eaf in Mac and PC simultaneously (on two separate computers) and click on the end of the same annotation (from the same file), the same sign, with the same time stamp (11:036), I see something different in each video. It is clearly only about 1 frame difference but it’s strange. Does it relate to the number of frames that each media player can show and so in one of them, it shows the next frame? Or could it relate to different versions of ELAN?
I’m not sure I understood what you suggested as being the issue. But I wanted to ask, is there a solution?
Thanks,
Rose 
Hi Rose,
Thank you for the clarification, it confirms my interpretation of the problem.
I don’t think the difference has anything to do with the ELAN version; in both cases ELAN tells the media player to go to media time 11:036, it’s up to the player to show the corresponding video frame.
The chance of seeing two different frames on two different computers is probably less if both computers are of the same type (both Macs or both Windows PC’s), but even then there can be differences.
I’ve seen, for example, with some .mp4 files, that on one and the same pc, the frame shown when activating an annotation (the media player jumps to the frame of the begin time of the annotation) depended on whether the player was to the right or to the left of the annotation prior to the jump (i.e. a jump backward vs a jump forward).
The only way to eliminate/reduce that problem in such case, is to use videos consisting of i-frames (key frames) only (which may not always be an option if a project is already ongoing).
-Han