Sure. In Tab "Project Options" you let the user define a current "Identifier" label, imagine it is "my-dreams", because the user wants to start a video-log of her dreams.
She wakes up, and starts the app, with "my-dreams" as current identifier. In the "Live Camera Video" she eventually writes something into the "Optional Recording Label" field, that is a title for the dream she's going to record - but this has not to be considered as part of the "identifier", i.e. the identifier is still "my-dreams".
While recording, she can pause and insert tags, then resume. Also, she'll be able to add tags when the recording will end. And also, when she'll have a video selected into the "Media File Viewer" Tab.
The process of tags insertion is done by viewing a list of all the tags defined for videos with the same identifier (in this example, "my-dreams"), sorted by descending number of total occurrencies, and writing something into an input field; while writing, the list dynamically changes on every keypress, filtering out tags that don't contain the written string. On the right of the input field there is a [ADD] button, that when pressed clears the field and puts that string into the bucket of tags for the current video. Also, hovering on the tags in the dynamic list retrieved from the videos with same identifier, a [ADD] button appears, that when pressed puts that tag into the bucket of tags for the current video. Hovering on the tags in the bucket of tags defined for the current video, a [DEL] button appears, that when pressed deletes that tag for the current video.
Note that if the user defines also e.g. a "startup-ideas" identifier, and records videos with it, the list of tags for that identifier of course won't include those added to videos of "my-dreams" identifier, but only those added to videos of "startup-ideas" identifier.
If it's not clear, or if you want/can do it in some other way, let me know.
EDIT: errata corrige: "dreams" -> "my-dreams"
EDIT: [TAG] button -> [ADD] button