W3C Media Fragment is being used here to specify the start/end time and the spatial area of interest (bubble note).
Placement of the "bubbles" are relative to the video size
<exif:width rdf:datatype="http://www.w3.org/2001/XMLSchema#integer">480</exif:width> <exif:height rdf:datatype="http://www.w3.org/2001/XMLSchema#integer">270</exif:height>
If the video is rendered at a different size then the bubbles will have to be resized / re-placed accordingly.
With RDF annotations, it's possible to fetch annotation resource from a different location. For example: overlaying a Flickr image on top of a video.