I have always had a strange obsession with the media we use to store music. Back in elementary school I loved using our home tape recorder to make mix tapes. It left me with so many good memories. These days my dream is to own my own cassette Walkman.

But this is not easy to pull off. Walkmans are expensive and come with plenty of headaches. (My birthday wish this year was that some kind friend would gift me one. But I know you would call me shameless for even thinking it.)

To fill that deep consumerist void, half a year ago I settled for buying a Fiio Echo Mini. It is an MP3 player designed to look like a mini cassette machine.

I'm in the mood to tell a little behind-the-scenes story about the complex technical journey of a seemingly simple interactive video player and how it works today. This article will be split into two parts: a history lesson and an overview of the current technical architecture.

This piece will focus on the process of identifying and solving problems, and how we used architectural design to reorganize business requirements and create sensible abstractions. For me, this is a record of a chapter in my life; for you, the reader, I hope it can be inspiring.

If I asked you "Who are you?", you might tell me your name. If I asked again, you might tell me your gender, your profession, your hometown, your hobbies. But what if I asked a third time? Most people would probably call me crazy and walk away, but perhaps some would begin to seriously discuss who they really are.

You may not have explicitly asked yourself "Who am I?", but you've probably been curious about it. Some people, to satisfy this curiosity, turn to astrology and fortune-telling to understand their past and future. Others take psychological tests, trying to distill personality into symbols.

These are all good approaches—I'm somewhat familiar with them myself. But after experiencing them firsthand, I always felt their answers were bland, unable to satisfy me. So I thought, maybe this time I should do something serious about it.

I'm sure you have, at some point, seen those little ads for "essay writing services" in the bathroom stalls of a university administration building. You and I should have a consensus on this business: having someone else complete your thesis is unethical. In an era where the AI storm is sweeping the world, the one doing the "ghostwriting" no longer needs to be a real person. A quick search for online large language model services will reveal a plethora of flashy websites.

Initially, schools maintained a high level of vigilance against this trend, banning students from using such services for homework and papers, and adding an "AI writing detection" step to the graduation thesis review process. However, as prompt engineering becomes more refined, and various new models and fine-tuned versions appear one after another, the early detection services designed for a single model like GPT will likely become unable to handle these complex situations. Furthermore, as the conversational style of large language models continues to permeate the internet, the writing style of readers will also begin to converge with that of generated text. All these changes point to a clear outcome: it is becoming increasingly difficult to determine whether the author of a piece of writing is a real person.

Whether you have sought it out or not, I imagine you have seen plenty of "AI bloggers selling courses online." The most common narrative is, "This is the era of AI. If you don't learn now, you will be left behind," as if the world will end tomorrow if you don't buy their course today. Does this feel at all familiar to you, the reader?

Let's try this: "Don't let your child lose at the starting line." "First grade is the most important year." "If they fall behind in second grade, they'll never catch up." (Please mentally fill in the rest for third through sixth grade.) "The transition to middle school is a crucial moment in life." (Please continue to fill this in all the way to the college entrance exams.) Once in college, you'll be asked, "How can you sleep at your age?" And after starting work, someone else will say, "If you don't learn how to use AI, you're finished!"

Wow. Cool.