This may not be where you read it, @JACOBSEN_C , but I found this news release about partnering with Speechmatics from 2017. It says that Canvas is using their speech-to-text transcription service.
The rest of this is educated speculation:
I think it would be necessary for Arc to send the transcripts back to the transcription service for any learning or improvement to happen. As it is, I think it's a separate, one-time, and one-way process. They transcribe the file and pass off a transcript to Arc, but Arc has its own caption editor and doesn't send changes back.
That is how most of the stand-alone services work. I looked into different services (Google, AWS, Watson) when I wasn't happy with Arc's translation editing capabilities and most of them worked by sending a file and getting back a transcript or captions.
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