Making `tfjs` runtime the default

[ziyuan-linn]

After discussing with @shiffman, I am creating an issue to start a discussion about potentially switching our default runtime to tfjs instead of mediapipe.

The MediaPipe runtime has been causing some issues:

• Unable to load two models at the same time: #69
• Memory leak: #129

The TFJS runtime, although slightly worse in performance, seems to be more stable and without the above issues. I think it might be a good idea to set the tfjs runtime as the default for all models and have mediapipe as a more "experimental" option.

Please share your thoughts on this @gohai @MOQN!

[gohai]

I too would pick stability over performance, if the better-performing avenue is having those other drawbacks that impact the experience of folks using it.

Just to share some thoughts on the issues @ziyuan-linn mentioned (in case we want to explore addressing those still):

• Unable to load two models at the same time: I am wondering if we could work around this with a synchronization mechanism, where the parent ml5 object keeps a promise (or an array of promises) that get fulfilled whenever a model finishes loading? And a helper function that waits for no outstanding promises before returning? This function could be sprinkled in to the classes that need it?

• Memory leak: those seem to be notoriously hard to get to the bottom of... I'd do the same approach as you already did - checking if this also occurs in tfjs example codes, and filing bugs against them if yes, and seeing if there is anything we're doing differently if not

[shiffman]

Thank you for the thoughts @gohai! @ziyuan-linn let's go ahead and switch over to tfjs for the upcoming soft launch! We can keep issues open and revisit in the future.