More control of video playback from experiment.py files.

[davidt0x]

Allow writing experiment.py files (e.g. to present video1 for 60 sec, then randomly sample among videos 1, 2, and 3 for 15 sec each for a total of 180 sec, then present video 1 for 60 sec). Max has kindly helped me take a look at this but we haven't figured out an elegant solution. The current set up writes a new playlist instance/toc line for every single video frame, this is not good. The current workaround is to run a separate flyVR experiment for the different stimulus segments, or hardcode the order of these items using a long and repetitive playlist.

[nzjrs]

Not sure about the one TOC per frame, that seems odd, but there should already be enough hooks in the Experiment base class to achieve the experiment you describe - you might pay the setup latency cost, but a play_backend_item call with correctly formatted yaml payload should work