Allow adding ruler markers
Submitted by Jeff F.T.
The ability to add markers, which would appear above the ruler (or maybe below it?) and be used for arbitrary visual reminders for the user (ex: identify a portion of the timeline as "scene 44" or "needs color grading", etc.). They should be label-able, movable, deletable, etc.
Markers would be added with double-clicking the ruler or with a shortcut such as "m". When adding a marker, its label should be highlighted in edit mode to allow typing a name directly. Pressing Enter or clicking anywhere on the timeline would exit the label editing mode.
Saving and loading of the markers in the
xges project file requires changes in GES, see [[ http://lazka.github.io/pgi-docs/#GES-1.0/classes/Formatter.html#GES.Formatter | GES.Formatter ]].
It would be an easy an fun feature for someone to get acquainted with the Pitivi timeline/ruler.
Imported from https://bugzilla.gnome.org/show_bug.cgi?id=608682