I've done a lot of work with the Watson Speech to Text service (I work on the Watson team), and I've been pretty impressed with the results. You can upload an audio file (wav, flac, or ogg/opus) to the demo to try it out: https://speech-to-text-demo.mybluemix.net/

Nuance has a suite that does that. We use their software and it's pretty good—despite being a headache to configure. But it's neither free nor open source.

This is also what Castingwords does - if you want high quality results transcribed by people. https://castingwords.com/support/transcription-api.html

We use Speechmatics (and sphinx) for caption alignment and timestamps. We certainly recommend them if that’s the service you need.

that's exactly what we do at speechmatics.com - feel free to give us a try and make the most of the free credits

Google will start giving this service. https://cloud.google.com/speech/