APIs:
- ges_timeline_get_frame_time
- ges_timeline_get_frame_at
- ges_clip_asset_get_frame_time
- ges_clip_get_timeline_time_from_source_frame
Extracting ges_util_structure_get_clocktime to internal utilities adding
support for specifying timing values in frames with the special
f<frame-number> synthax.