I often ponder which programming language is the optimal choice for cross-platform application development. It's not just a casual debate; there's a genuine need for efficient and cost-effective solutions in the field of web programming, especially when it comes to creating applications for major desktop operating systems such as Windows, Linux, and macOS.

The primary goal is to ensure that the applications remain native to each operating system in terms of design and functionality, providing users with a seamless experience. The decision between Java, C#, and C++ becomes crucial in this context.

The core functionality of the application involves accessing a web server via HTTP, handling various data formats including popular audio/video codecs, caching media content and text, and supporting JSON. Additionally, it's essential that the chosen language is easy to learn, particularly for individuals transitioning from platforms such as Delphi.

In summary, the quest for the most suitable language for cross-platform application development isn't just a theoretical debate; it's a practical necessity in the realm of web programming, where efficiency, cost-effectiveness, and user experience are paramount.

In the quest for an optimal solution, it's imperative to consider several key factors. Firstly, the chosen language must effectively cater to the unique requirements of major desktop operating systems like Windows, Linux, and macOS, ensuring that the applications deliver a seamless and native user experience across these platforms. This demands careful consideration of design and functionality to maintain consistency and usability.
The core functionality of the application involves intricate tasks such as accessing a web server via HTTP, handling diverse data formats including audio/video codecs, caching media content and text, and supporting JSON. Therefore, the selected language should possess robust libraries and tools to efficiently execute these operations while maintaining performance and reliability.

Ease of learning is a crucial aspect, especially for individuals transitioning from platforms like Delphi. The language should offer a gentle learning curve to facilitate a smooth transition and ensure productivity from the outset.

Amidst the myriad of programming languages available, contenders like Java, C#, and C++ stand out for their capabilities in addressing these requirements. Each language brings its own set of advantages and considerations, making the decision a weighty one.
The pursuit of the most suitable language for cross-platform application development transcends theoretical debates to become a real-world imperative in the sphere of web programming. The stakes are high, encompassing efficiency, cost-effectiveness, and, above all, user experience. It's an ongoing endeavor, demanding astute analysis and strategic decision-making to seamlessly bridge the realms of technology and user needs.

A century ago, I used to code in C++. As of today, I have shifted my focus from C# to Java.

Java aligns with your requirements seamlessly. You have the flexibility to incorporate native look&feel in Java Swing (a GUI library), ensuring that the application on every operating system looks like a native one.

Java boasts an extensive collection of free libraries. Explore Apache Commons by Google for comprehensive support on various functionalities.

For multimedia processing, delve into Java Media Framework by Google.

The language itself is graceful and refined, although veteran C++ developers might not entirely agree with me on this. And I wouldn't be the only one facing their disagreement.

I deal with JS + WebSocket|ajax. The system requirements will only cater to the latest browser builds, so there is no need to delve into complicated workarounds. This approach is the most efficient and optimal given the specified requirements, as everything needed is readily available. Just remember not to overlook the manifest.

The only potential issue may arise with codecs. However, by installing extension packages to browsers, any complications can be resolved. Of course, if it's a custom job, the situation might differ.

For more complex tasks, I would recommend C++ and QT(QScript) straightforwardly. It provides a webkit and fulfills all the necessary criteria. However, for someone transitioning from Delphi, mastering the pros might be a bit challenging. Nevertheless, QT boasts powerful editors, particularly beneficial for a delphi developer looking to streamline their work with qtdesigner.

As for Java, I suggest taking a cautious approach. Given the requirements you've outlined, it may not be the most resource-efficient choice to opt for such a robust language.