Neden — Learn languages with videos
Built a desktop video player for language learning, with dual subtitles, word meanings, AI explanations, and subtitle tools, plus a plugin that brings the same lookups to IINA on a Mac.
Learn a language from the shows you already watch
Neden is a desktop video player for learning a language. Show the original dialogue next to a translation, click a subtitle word for its meaning, or select a phrase to pause playback and open an explanation beside the video. You can ask follow-up questions in the same conversation.
I designed the product and built the Qt Quick player, the hosted API, the website, and the packaging. A separate plugin brings the same lookups to IINA, a video player for Mac, using a TypeScript plugin and a Swift helper.
A player built for study
Subtitles you can study from
The player shows two subtitle tracks at once, keeps a searchable transcript, replays the current line, and remembers where you stopped. Hovering a subtitle word opens its meaning, and phrase explanations return a translation followed by a breakdown that covers every spoken word.
Flashcards inside the playback workflow
Local flashcards let you save what you looked up and review it later. A remembered card comes back after a longer gap each time, and a missed card returns in ten minutes. Cards export as TSV.
More than one language
A validated language catalog drives word lookup, which preserves Unicode and uses native segmentation for scripts written without spaces. Checks cover Arabic, Chinese, Japanese, Hindi, Persian, Cyrillic, and Latin text.
Subtitle tools
Repair timing between two tracks
The player searches up to two minutes of offset and common frame-rate drift, refines the match, and rejects alignments that are ambiguous. Manual time anchors are available, and a track never changes until you confirm.
Translate with AI without leaving half a file
AI translation keeps every cue’s timing, sends eight cues at a time with neighboring dialogue, and checks the returned sequence. A completed track loads only after every batch succeeds, so cancelling or a malformed response never leaves a partial file.
Find subtitles and read embedded ones
The player searches and downloads from subtitle providers, with size limits and checks on every download. It also extracts embedded Matroska and MP4 subtitle tracks with bundled FFmpeg libraries, removes styling, and keeps the timing.
Word lookup and phrase explanations in IINA
In the IINA plugin, clicking a word opens a small card over the video. You can choose Google Cloud Translation or Microsoft Translator and supply your own key. Google returns one translation. Microsoft’s English dictionary can offer alternatives, falling back to translation when it doesn’t have an entry.
Selecting a phrase opens the AI sidebar. The prompt asks for its natural meaning, a breakdown of the selected words, and grammar where useful. The full subtitle line and neighboring cues provide context.
In the scene shown here, word lookup returns “broken” for “bozuk.” In the expression “moralin bozuk,” the meaning is closer to feeling down.
Streaming answers during playback
A Swift helper for streaming in IINA
The IINA HTTP API I inspected didn’t let me display an answer as it arrived. I built a Swift helper to receive the response in chunks, then pass the text to the TypeScript sidebar. I tested how it handles responses split across chunks, interrupted connections, and timeouts.
Discarding late responses
Each explanation captures its selection, subtitle cue, and neighboring context as a snapshot and tags the request with its owner. A new selection, track change, seek, or different movie can make an in-flight response irrelevant, so a stream that arrives late cannot overwrite the current answer. Stop leaves a partial answer visibly incomplete.
A second provider when the first is slow
An optional fallback starts a second provider after five seconds without an answer. It never switches once text has started, lets you reorder the two providers, and warns that both attempts may be billed.
Pause, resume, and replay
Selecting a phrase pauses the video so you can read the explanation. Replay line lets you listen to the same phrase several times to get familiar with how it sounds. Each press plays the selected subtitle line once, then returns to your previous position in the episode. You can close the panel to return to watching and reopen it to continue the conversation.
Source and translated subtitles
You can display the original dialogue alongside a translation and select words or phrases from the source subtitle. The controls let you choose and swap the tracks, adjust their appearance, and include the translation in AI context. Neden saves your track choices for each movie.
Screenshots show the installed plugin during a Leyla ile Mecnun episode, with Turkish and English subtitles.
Provider requests and saved keys
Requests go directly to the learner’s configured providers. Word lookup sends the clicked word; phrase explanations send the selection, its cue, nearby subtitle context, and conversation turns. The video and complete subtitle file are not uploaded.
Neden stores provider and subtitle-service keys in the operating system’s credential store, with no plaintext fallback, and binds each key to its API origin. In the IINA plugin the Swift helper receives keys through private pipes, which avoids putting credentials in command arguments.
I also built an invitation-only hosted AI tier. It signs in through the browser, keeps refresh tokens in the keychain, runs Stripe checkout with verified webhooks, and reserves each account’s usage allowance in a Durable Object before any provider call, so concurrent requests cannot overspend.
I restricted how model responses are rendered and added validation for subtitle files and messages from the interface.
Packaging and tests
I built installers for macOS, Windows, and Ubuntu. Each build records its source revision, checks pinned source archives and dependency notices, and a CI smoke test installs the package and checks decoded video pixels. A software OpenGL fallback fixed video failures on some Windows graphics drivers.
Automated tests cover the IINA plugin, the hosted API, and the desktop player, including native interface checks and a scenario runner that drives the real QML interface against a mock AI service.
Website and source code
Visit the Neden website to see how it works and download the app.
The source is available on GitHub, including the Qt Quick desktop player, the TypeScript IINA plugin, the Swift streaming helper, and the hosted API.
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