I touched on the video APIs above, but regarding transcription - I have a lot of thoughts.
We chose to work with AssemblyAI (https://assemblyai.com) after trying AWS's transcript service, RevAI and Google's Speech-to-text API.
First, we started with doing manual transcripts through Rev, but the cost was unmanageable at scale. We were really happy with the quality, but couldn't charge $100 per video, so we needed a cost-effective automated solution.
I then found an old blog post from Descript's co-founder Andrew Mason, who talked about which speech-to-text API they decided to use. The blog post is old, so the metric used are going to be irrelevant, but I was impressed they decided to use Google's API.
We implemented the GCP option, I was shocked how slow it was and how expensive it was. For one, the quality wasn't that great, and to use the lower cost option (audio-only), you need to do some additional FFMPEG based transcoding, which is very error prone. Because we receive a range of video types from users, it was causing more problems than was worth dealing with. Also the time lost made the cost savings irrelevant.
Enter - AssemblyAI.
I did some research around what other companies were using today, and saw they have great ratings on G2 (https://www.g2.com/products/assemblyai-speech-to-text-api/re...). The CEO jumped on a call on a Sunday, when I was trying to improve our transcript processing time, and after testing the API, I was shocked that the transcript quality was closer to the human done transcripts I was getting, at a cost significantly cheaper than the Google option.
Conclusion - we needed speed, quality, low-cost and support. AssemblyAI won on all these fronts.