Beginner question: What are vertical lines with arrowheads in timeline / why some titles won't rende

Hi,

New to FCP, so my apologies for what must be obvious. (I did read the entire manual and found no mention).

My movie is ready to render and two vertical lines, each with an arrowhead appeared (see screenshot). I must have selected something unknowingly. Now when I render (share to master file), only the first (frozen) frame renders until that section is over, and for the remaining the titles don't appear.

Any help will be greatly appreciated!

What that indicates is that you are editing inside a clip or inside a compound clip and are not editing inside a project. You may have marked in and out on a clip and then used the Open Clip function rather than edit it into a project.

Yes, Tom got it. Notice the hash lines indicating media outside of the Compound in the original Timeline.
If you double-click a compound clip, it opens into its own Timeline.
help.apple.com/finalcutpro/mac/10.3/#/verca9e8672