SmartSub

SmartSub takes audio or video and produces translated subtitles, start to finish, on your own machine. It transcribes speech to text, translates it, lets you proofread against a video preview, then burns the subtitles into the video or muxes them as a soft track. Nothing gets uploaded, which matters if you're working with footage you can't send to a cloud service. MIT-licensed and free on Windows, macOS, and Linux.

It ships six transcription engines, including whisper.cpp and faster-whisper that run fully offline, and hooks into 17+ translation providers from Google and Baidu to Gemini, DeepSeek, and any OpenAI-style API. GPU acceleration covers NVIDIA CUDA, AMD and Intel via Vulkan, and Apple Metal, with automatic detection and CPU fallback. Setup is heavier than a pure web tool: you download models, pick an engine, and configure providers, but it's a desktop install, not a server.

Solo creators and translators: this is a strong free alternative to paid subtitle services, and the local engines cost nothing to run. Small teams doing video work: same, with no per-seat fee. Large teams: workable, though there's no central account or shared workflow.

The catch: "free" stops at the app boundary. The bundled offline engines are free, but the moment you wire up Gemini, DeepSeek, or a cloud translation API for better quality, you're paying those vendors per use on your own keys. Stick to whisper.cpp and faster-whisper and it's genuinely free end to end.