Experimental ttconv implementation by popular demand

By popular demand, ttconv has an experimental implementation for converting popular timed text formats to SCC aka CTA/CEA 608.

Demo at:

https://ttconv.sandflow.com/

Code and issues at:

https://github.com/sandflow/ttconv/pull/441

Time to kick the tires! Looking forward to the feedback.

#cea608 #captioning #ttml #vtt #imsc #cta608