How does not using -a (-duplicates) option choose?

[handvprice]

I have an older .avi video file from a Casio. Using "exiftool -s -a -G1 -DateTimeOriginal" shows two results, slightly different:  [RIFF] 2009:07:30 15:42:00, and [ExifIFD]  2009:07:30 15:42:48 (the video is 21 sec long). If I don't use -a, it chooses the [ExifIFD] version only. Leaving aside the question of why it has 2 times, I'm simply wondering how exiftool chooses which to present if there are different duplicates? Is there a heirarchy of "more reliable" or "more usual" groups, or is it random, or whichever it comes across first, or ?

TY.

[StarGeek]

Whatever it comes across last. 

This is why the Composite tags always have priority, as they are computed last.  This is useful in cases like GPS coordinates, where if you had a Southern hemisphere latitude, which is a negative number, exiftool doesn't just return the EXIF:GPSLatitude, which is always a positive number because the hemisphere reference is held in a different tag.  The Composite:GPSLatitude is created by combining the GPSLatitude and GPSLatitudeRef to get the complete coordinate.

[Phil Harvey]

StarGeek is correct, the default rule is that the last one in the file takes precedence.  But there are exceptions:  For example, in TIFF files, tags in the primary image IFD take priority.

- Phil

[StarGeek]

**takes notes**

[handvprice]

TY for the definitive answers!