createWasmRuntime function
VM stub: there is no ffmpeg.wasm outside the browser.
Native platforms encode through ProcessFfmpegRunner; this factory is
only reachable when something on the VM asks for the web runtime, which
is a wiring bug worth failing loudly on.
Implementation
WasmRuntime createWasmRuntime() => throw UnsupportedError(
'ffmpeg.wasm is web-only: createWasmRuntime() has no VM implementation. '
'Use ProcessFfmpegRunner on native platforms.',
);