terryops

Hi HN, I built tools.video (https://tools.video) — 18 free video and audio tools that run entirely in your browser. Files never leave your machine.

Compress, convert, trim, crop, resize, merge, rotate, reverse, speed change, screenshot, mute, video-to-GIF, audio extract/trim/convert/merge/speed, and media info.

The interesting technical problem: FFmpeg compiled to WASM works, but it tops out around 4 GB, runs single-threaded, and is 10x slower than native browser APIs for the same operations. I wanted to handle 50 GB files and actually use the hardware (theoretically there's no limit at all).

So I built a hybrid engine:

- Most tools use WebCodecs (via MediaBunny) — the browser's native hardware-accelerated video encoder/decoder. H.264, HEVC, VP9, AV1 with GPU acceleration when available. This is what makes it fast. - Three tools (speed, merge, video-to-GIF) still use FFmpeg WASM where WebCodecs can't do the job. - The engine auto-detects which path to use and falls back gracefully — if hardware encoding fails, it retries in software; if WebCodecs can't handle a codec, it routes to FFmpeg.

How 50 GB works in a browser:

Files are streamed through OPFS (Origin Private File System) with chunked I/O. Small files (<256 MB) stay in memory. Larger files write to OPFS-backed storage. The biggest files use StreamTarget for chunked streaming so you never buffer the entire output in RAM. Stale temp files auto-clean after 6 hours, and quota-exceeded errors trigger aggressive cleanup mid-operation.

Other details HN might find interesting:

- Processing runs in a Web Worker with stall detection (180s timeout). If the worker crashes, it falls back to main thread automatically. - Audio extraction with stream copy (no re-encoding) skips disk I/O entirely — zero-copy transmux via BufferTarget. - Codec extensions (MP3, FLAC, AAC, AC3 encoders as WASM) are loaded on demand but can't run in the Worker — esbuild corrupts their inline WASM binaries during double-bundling, so they route to main thread. - 30+ formats, 5.1/7.1 surround audio preserved, 19 languages.

There's a /benchmark page if you want to compare the WebCodecs path vs FFmpeg WASM directly with audio extraction.

Built with Next.js 15, React 19, TypeScript, Tailwind v4, Zustand.

Would love feedback — especially on formats/codecs you'd want supported, or edge cases where processing fails.

Last year, I got the amazing news that I was going to be a dad. My wife, who’s really into TV dramas—especially those focused on Japanese urban life and ancient Chinese romance—started watching a lot of shows while waiting for our baby to arrive. She couldn't get enough from Netflix and even subscribed to a 'local Netflix'. But she quickly ran into a problem: there were no translated subtitles for the shows she wanted to watch.

Being the go-getter she is, she tried various platforms like Happyscribe and Notta. Unfortunately, the transcription quality for Asian languages was just terrible, not to mention the translation quality. That’s when I decided to step in, get my hands dirty and fix it.

First Attempt

The solution is straightforward to me: First, get the video and extract the audio. Then, transcribe the audio into subtitles with high accuracy. Finally, translate those subtitles and watch the video with the synced, translated subtitles.

With the AI boom happening, I came across OpenAI's Whisper automatic speech recognition model and started thinking about how I could integrate it with ChatGPT.

For those who aren’t familiar, Whisper is renowned for its accuracy in most commonly used languages—though it struggles with unclear audio, which can lead to some hilarious hallucinations.

Setting it up was straightforward. It’s easy to use Whisper to transcribe audio into text with timestamps. I then used GPT for translation, synced the subtitle file with the original video in Adobe Premiere Pro for a quick check, and exported the video. This is how I translated and localized an episode of a Chinese TV series. The first show I experimented with was "Joy of Life."

By the way, watching a few episodes together was quite enjoyable.

However, Whisper ran slowly on my M1 Pro, and since I was also experimenting with generating images using Stable Diffusion, I decided to set up a PC with an NVIDIA RTX 4090. I configured a few scripts to download, convert to text, and translate in one go, speeding up the whole process significantly.

One day, while my wife was watching an episode, she suggested, "Why don’t you just make this into a product? Others might find it useful too, and you could even make some extra money for baby formula."

It was a eureka moment for me.

At the time, AI products were emerging rapidly, and with my previous project in the maintenance stage, I was eager to create something new. I invited two friends to join me, and we formed a small team. Thus, a new product was born.

Choices to Make

PC or Mobile: I chose to develop for PC instead of mobile. Subtitle editing and translation typically involve long videos, which are better handled on a PC. Web or Client: I opted for a web-based interface over a client-side application. Client applications need to be compatible with both Windows and Mac, and different versions of these systems. Moreover, I was fed up with Whisper's slow speed and various model limitations. Offloading the computation to the cloud allows users with any computer configuration to use this service smoothly.

I decided to name the product "SubEasy" because it makes creating subtitles easy.

So, it's SubEasy.ai

see comments below to continue...