In Hookpad 1 (the TheoryTab Drafts version), attached YouTube videos with a section starting at 0:00 will always begin a half beat too late (in relation to the chart). This leads to the Youtube playback tempo being ever so slightly faster than the actual tempo, making it difficult to sync the melody with the music.
I know that Hookpad 2 is higher priority, but at least have a non-buggy version of HP1 if you are going to keep it for TheoryTab for the time being.
This screenshot was taken just after pressing P to play the video.