There's quite a bit of overhead in execing and piping data from ffmpeg. If performance is a concern, then using the C ffmpeg API is a better bet(see pyav for a good example of this) . Cool project though!
I didn't say that the book's approach contradicted TDD, I'm merely quoting from the book and refuting one its claims (that TDD doesn't lead to good design). I agree that narrow and deep modules support refactoring internals if their unit tests are written to treat them as black boxes.
I strongly agree with your first two points. Good naming supplants the need for commenting.
I find diagrams a far terser communication tool of architecture than comments.
I bought this book off the back of the referenced discussion trashing Clean Code. Whilst Clean Code has its problems, well articulated in that previous discussion, I am loathe to recommend this book. A large part of it is dedicated to commenting practices and seems a bit out of touch with the way software is developed today. There were some rather dubious claims on TDD as well, suggesting that it aims to 'get features working, rather than finding the best design' which seems to completely ignore the refactoring phase practised in a TDD cycle. A choice quote about comments that I strongly disagreed with: "without comments, you cannot hide complexity". The book also strongly advocates for large classes and considers small ones an anti-pattern called 'classitis'.
I'd say half the book contained good advice, the other half was mediocre or dubious at best.
I'm curious to hear what others think who've read both books.