This is a Blender 2.77 tutorial on how to speed up a Video Sequence Editor / Scene render overlay by many times.
You can download the starter project, which is actually the ending of my Screencast Balloons tutorial, at Google Drive (only 4.8 MB):
https://drive.google.com/file/d/0B9ol...
You can download the Python script output_file_node.py created in the tutorial at Google Drive:
https://drive.google.com/file/d/0B9ol...