Whisper is pretty good and open source, you just need to write your own script to do the automation.

And then you can also use some summarisation with OpenAI to create short summaries for each lecture or extract highlights or key points.

You can then upload them to Obsidian to make them indexed and searchable and can use any of their plugins to make it even better.

And you can use Syncthing to sync it to your phone.