decoder_worker.js

/**
 * Decoder Worker - Runs adapter + decoder in a separate thread
 */

importScripts('https://cdn.jsdelivr.net/npm/onnxruntime-web@1.17.0/dist/ort.min.js');

// Configure ONNX Runtime to find WASM files from CDN
ort.env.wasm.wasmPaths = 'https://cdn.jsdelivr.net/npm/onnxruntime-web@1.17.0/dist/';

const MODEL_CACHE_NAME = 'moonshine-models-v1';

// Helper to fetch model with progress reporting and caching
async function fetchModelWithProgress(url, modelName) {
    // Try to get from cache first
    try {
        const cache = await caches.open(MODEL_CACHE_NAME);
        const cachedResponse = await cache.match(url);

        if (cachedResponse) {
            const buffer = await cachedResponse.arrayBuffer();
            self.postMessage({
                type: 'progress',
                model: modelName,
                loaded: buffer.byteLength,
                total: buffer.byteLength,
                done: true,
                cached: true
            });
            console.log(`${modelName} loaded from cache`);
            return buffer;
        }
    } catch (e) {
        console.warn('Cache API not available:', e.message);
    }

    // Fetch from network
    const response = await fetch(url);
    if (!response.ok) {
        throw new Error(`Failed to fetch ${modelName}: ${response.status}`);
    }

    const contentLength = response.headers.get('Content-Length');
    const total = contentLength ? parseInt(contentLength, 10) : 0;

    if (!response.body || !total) {
        // No streaming support or unknown size - just download
        const buffer = await response.arrayBuffer();
        self.postMessage({
            type: 'progress',
            model: modelName,
            loaded: buffer.byteLength,
            total: buffer.byteLength,
            done: true
        });
        // Cache the response
        try {
            const cache = await caches.open(MODEL_CACHE_NAME);
            await cache.put(url, new Response(buffer.slice(0)));
        } catch (e) {
            console.warn('Failed to cache model:', e.message);
        }
        return buffer;
    }

    const reader = response.body.getReader();
    const chunks = [];
    let loaded = 0;

    while (true) {
        const { done, value } = await reader.read();
        if (done) break;

        chunks.push(value);
        loaded += value.length;

        self.postMessage({
            type: 'progress',
            model: modelName,
            loaded,
            total,
            done: false
        });
    }

    self.postMessage({
        type: 'progress',
        model: modelName,
        loaded: total,
        total,
        done: true
    });

    // Combine chunks into single ArrayBuffer
    const result = new Uint8Array(loaded);
    let offset = 0;
    for (const chunk of chunks) {
        result.set(chunk, offset);
        offset += chunk.length;
    }

    // Cache the result
    try {
        const cache = await caches.open(MODEL_CACHE_NAME);
        await cache.put(url, new Response(result.slice(0)));
        console.log(`${modelName} cached`);
    } catch (e) {
        console.warn('Failed to cache model:', e.message);
    }

    return result.buffer;
}

// Model config
let cfg = null;
let tailLatency = 0;

// Decoding config
const TOKENS_PER_SECOND = 6.5;  // Max tokens per second of audio
const FRAME_DURATION_MS = 20;   // Each encoder frame is 20ms

// Check for repetitive token patterns that indicate decoding should stop
function hasRepetition(tokens) {
    const len = tokens.length;
    if (len < 5) return false;

    // Check if last 5 tokens are the same
    const last5 = tokens.slice(-5);
    if (last5.every(t => t === last5[0])) {
        return true;
    }

    // Check for 3 repeated same pairs (e.g., [A,B,A,B,A,B])
    if (len >= 6) {
        const pair1 = [tokens[len - 6], tokens[len - 5]];
        const pair2 = [tokens[len - 4], tokens[len - 3]];
        const pair3 = [tokens[len - 2], tokens[len - 1]];
        if (pair1[0] === pair2[0] && pair2[0] === pair3[0] &&
            pair1[1] === pair2[1] && pair2[1] === pair3[1]) {
            return true;
        }
    }

    // Check for 2 repeated same triples (e.g., [A,B,C,A,B,C])
    if (len >= 6) {
        const triple1 = [tokens[len - 6], tokens[len - 5], tokens[len - 4]];
        const triple2 = [tokens[len - 3], tokens[len - 2], tokens[len - 1]];
        if (triple1[0] === triple2[0] &&
            triple1[1] === triple2[1] &&
            triple1[2] === triple2[2]) {
            return true;
        }
    }

    return false;
}

// Sessions
let adapterSession = null;
let decoderInitSession = null;
let decoderStepSession = null;

// Decoder state
let crossCache = null;
let selfCache = null;

// Tokenizer
let tokenizer = null;

// Accumulated features
let accumulatedFeatures = null;
let currentSegmentId = null;

// Live caption throttling to prevent pipeline backup
let isDecoding = false;
let lastDecodeTime = 0;
let pendingDecode = false;
const MIN_DECODE_INTERVAL_MS = 500;  // Don't decode more often than every 500ms for live captions

class MoonshineTokenizer {
    constructor() {
        this.decoder = null;
        this.vocab = null;
    }

    load(tokenizerJson) {
        this.vocab = tokenizerJson.model.vocab;
        this.decoder = Object.fromEntries(
            Object.entries(this.vocab).map(([k, v]) => [v, k])
        );
    }

    decode(tokenIds, skipSpecial = true) {
        const specialTokens = new Set([0, 1, 2]);
        let text = '';

        for (const id of tokenIds) {
            if (skipSpecial && specialTokens.has(id)) continue;
            const token = this.decoder[id] || '';
            text += token;
        }

        // Handle various space placeholder representations
        text = text.replace(/\u0120/g, ' ');  // Ġ (GPT-2 style)
        text = text.replace(/Ġ/g, ' ');       // Literal Ġ character
        text = text.replace(/▁/g, ' ');       // SentencePiece style (U+2581)
        text = text.replace(/\u010a/g, '\n'); // Newline marker

        return text.trim();
    }
}

async function runAdapter(features, dims) {
    const feeds = {
        'encoder_output': new ort.Tensor('float32', features, dims)
    };
    const results = await adapterSession.run(feeds);
    return results.context;
}

async function initDecoderCache(context) {
    const feeds = { 'context': context };
    const results = await decoderInitSession.run(feeds);

    // Store cross-attention cache (even-indexed layers)
    crossCache = [];
    for (let i = 0; i < cfg.depth * 2; i++) {
        if ((i + 1) % 2 === 0) {
            crossCache.push({
                k: results[`cache_${i}_k`],
                v: results[`cache_${i}_v`]
            });
        }
    }

    // Initialize empty self-attention cache
    selfCache = [];
    for (let i = 0; i < cfg.depth; i++) {
        selfCache.push({
            k: new ort.Tensor('float32', new Float32Array(0), [1, cfg.nheads, 0, cfg.head_dim]),
            v: new ort.Tensor('float32', new Float32Array(0), [1, cfg.nheads, 0, cfg.head_dim])
        });
    }
}

async function decodeStep(tokenId, position) {
    const feeds = {
        'token_id': new ort.Tensor('int64', BigInt64Array.from([BigInt(tokenId)]), [1, 1]),
        'position': new ort.Tensor('int64', BigInt64Array.from([BigInt(position)]), [1])
    };

    // Add cache inputs
    let selfIdx = 0;
    let crossIdx = 0;
    for (let i = 0; i < cfg.depth * 2; i++) {
        if ((i + 1) % 2 !== 0) {
            feeds[`in_cache_${i}_k`] = selfCache[selfIdx].k;
            feeds[`in_cache_${i}_v`] = selfCache[selfIdx].v;
            selfIdx++;
        } else {
            feeds[`in_cache_${i}_k`] = crossCache[crossIdx].k;
            feeds[`in_cache_${i}_v`] = crossCache[crossIdx].v;
            crossIdx++;
        }
    }

    const results = await decoderStepSession.run(feeds);

    // Update self-attention cache
    selfIdx = 0;
    for (let i = 0; i < cfg.depth * 2; i++) {
        if ((i + 1) % 2 !== 0) {
            selfCache[selfIdx] = {
                k: results[`out_cache_${i}_k`],
                v: results[`out_cache_${i}_v`]
            };
            selfIdx++;
        }
    }

    return results.logits;
}

async function decodeAccumulated() {
    if (!accumulatedFeatures || accumulatedFeatures.dims[1] === 0) {
        return '';
    }

    try {
        const context = await runAdapter(accumulatedFeatures.data, accumulatedFeatures.dims);
        await initDecoderCache(context);

        const numFrames = accumulatedFeatures.dims[1];
        // Calculate duration in seconds and max tokens based on that
        const durationSeconds = (numFrames * FRAME_DURATION_MS) / 1000;
        const maxTokens = Math.max(10, Math.floor(durationSeconds * TOKENS_PER_SECOND));

        const tokens = [1];  // BOS
        for (let step = 0; step < maxTokens; step++) {
            const logits = await decodeStep(tokens[tokens.length - 1], step);

            let maxIdx = 0;
            let maxVal = logits.data[0];
            for (let i = 1; i < cfg.vocab_size; i++) {
                if (logits.data[i] > maxVal) {
                    maxVal = logits.data[i];
                    maxIdx = i;
                }
            }

            tokens.push(maxIdx);

            // Stop on EOS
            if (maxIdx === 2) break;

            // Stop on repetitive patterns
            if (hasRepetition(tokens)) {
                console.log('Stopping decode due to repetition detected');
                break;
            }
        }

        return tokenizer.decode(tokens, true);
    } catch (e) {
        console.error('Decode error:', e);
        return '';
    }
}

// Helper to accumulate features data
function accumulateFeaturesData(data) {
    const newFeatures = {
        data: new Float32Array(data.features),
        dims: data.dims
    };

    if (accumulatedFeatures === null) {
        accumulatedFeatures = newFeatures;
    } else {
        // Trim last tailLatency frames from accumulated
        const numFrames = accumulatedFeatures.dims[1];
        const keepFrames = Math.max(0, numFrames - tailLatency);

        if (keepFrames > 0) {
            const totalFrames = keepFrames + newFeatures.dims[1];
            const combined = new Float32Array(totalFrames * cfg.dim);

            // Copy kept frames
            for (let f = 0; f < keepFrames; f++) {
                for (let d = 0; d < cfg.dim; d++) {
                    combined[f * cfg.dim + d] = accumulatedFeatures.data[f * cfg.dim + d];
                }
            }
            // Copy new frames
            combined.set(newFeatures.data, keepFrames * cfg.dim);

            accumulatedFeatures = {
                data: combined,
                dims: [1, totalFrames, cfg.dim]
            };
        } else {
            accumulatedFeatures = newFeatures;
        }
    }
}

// Message queue for sequential processing
const messageQueue = [];
let isProcessingQueue = false;

async function processMessage(e) {
    const { type, data } = e.data;

    switch (type) {
        case 'init': {
            try {
                cfg = data.cfg;
                const onnxUrl = data.onnxUrl;
                const modelName = data.modelName;
                const backend = data.backend || 'wasm';
                const dtype = 'fp32';

                const sessionOptions = { executionProviders: [backend] };

                tailLatency = cfg.n_future * cfg.encoder_depth;

                // Load tokenizer
                self.postMessage({ type: 'status', message: 'Loading tokenizer...' });
                self.postMessage({ type: 'model_start', model: 'Tokenizer' });
                const tokenizerResponse = await fetch(`${onnxUrl}/tokenizer.json`);
                const tokenizerJson = await tokenizerResponse.json();
                tokenizer = new MoonshineTokenizer();
                tokenizer.load(tokenizerJson);
                self.postMessage({ type: 'model_done', model: 'Tokenizer' });

                // Initialize adapter
                const adapterUrl = `${onnxUrl}/adapter_${modelName}_${dtype}.onnx`;
                self.postMessage({ type: 'status', message: 'Loading adapter...' });
                self.postMessage({ type: 'model_start', model: 'Adapter' });
                const adapterBuffer = await fetchModelWithProgress(adapterUrl, 'Adapter');
                adapterSession = await ort.InferenceSession.create(adapterBuffer, sessionOptions);
                self.postMessage({ type: 'model_done', model: 'Adapter' });

                // Initialize decoder init
                const decInitUrl = `${onnxUrl}/decoder_init_${modelName}_${dtype}.onnx`;
                self.postMessage({ type: 'status', message: 'Loading decoder (init)...' });
                self.postMessage({ type: 'model_start', model: 'Decoder Init' });
                const decInitBuffer = await fetchModelWithProgress(decInitUrl, 'Decoder Init');
                decoderInitSession = await ort.InferenceSession.create(decInitBuffer, sessionOptions);
                self.postMessage({ type: 'model_done', model: 'Decoder Init' });

                // Initialize decoder step
                const decStepUrl = `${onnxUrl}/decoder_step_${modelName}_${dtype}.onnx`;
                self.postMessage({ type: 'status', message: 'Loading decoder (step)...' });
                self.postMessage({ type: 'model_start', model: 'Decoder Step' });
                const decStepBuffer = await fetchModelWithProgress(decStepUrl, 'Decoder Step');
                decoderStepSession = await ort.InferenceSession.create(decStepBuffer, sessionOptions);
                self.postMessage({ type: 'model_done', model: 'Decoder Step' });

                self.postMessage({ type: 'ready', backend: backend });
            } catch (err) {
                self.postMessage({ type: 'error', message: err.message });
            }
            break;
        }

        case 'segment_start': {
            accumulatedFeatures = null;
            currentSegmentId = data.segmentId;
            isDecoding = false;
            lastDecodeTime = 0;
            pendingDecode = false;
            self.postMessage({ type: 'live_caption', text: '' });
            break;
        }

        case 'segment_end': {
            if (data.segmentId !== currentSegmentId) break;

            // Wait for any in-progress decode to finish before final decode
            while (isDecoding) {
                await new Promise(resolve => setTimeout(resolve, 50));
            }

            isDecoding = true;
            const text = await decodeAccumulated();
            isDecoding = false;

            self.postMessage({
                type: 'transcript',
                segmentId: data.segmentId,
                text: text
            });

            accumulatedFeatures = null;
            currentSegmentId = null;
            self.postMessage({ type: 'live_caption', text: '' });
            break;
        }

        case 'features': {
            if (data.segmentId !== currentSegmentId) break;

            // Accumulate this message's features
            accumulateFeaturesData(data);

            // Drain all pending features messages from the queue and accumulate them too
            while (messageQueue.length > 0 && messageQueue[0].data.type === 'features') {
                const nextMsg = messageQueue.shift();
                const nextData = nextMsg.data.data;
                if (nextData.segmentId === currentSegmentId) {
                    accumulateFeaturesData(nextData);
                }
            }

            console.log(`Decoder accumulated features, total: ${accumulatedFeatures ? accumulatedFeatures.dims[1] : 0} frames`);

            // Live caption with throttling
            const now = Date.now();
            const timeSinceLastDecode = now - lastDecodeTime;

            if (isDecoding) {
                // Already decoding, mark that we need another decode when done
                pendingDecode = true;
            } else if (timeSinceLastDecode >= MIN_DECODE_INTERVAL_MS) {
                // Enough time has passed, decode now
                isDecoding = true;
                lastDecodeTime = now;

                try {
                    const partialText = await decodeAccumulated();
                    self.postMessage({ type: 'live_caption', text: partialText });
                } finally {
                    isDecoding = false;

                    // If there was a pending decode request, schedule it
                    if (pendingDecode) {
                        pendingDecode = false;
                        setTimeout(async () => {
                            if (!isDecoding && currentSegmentId !== null) {
                                isDecoding = true;
                                lastDecodeTime = Date.now();
                                try {
                                    const text = await decodeAccumulated();
                                    self.postMessage({ type: 'live_caption', text: text });
                                } finally {
                                    isDecoding = false;
                                }
                            }
                        }, MIN_DECODE_INTERVAL_MS);
                    }
                }
            } else {
                // Too soon since last decode, mark pending
                pendingDecode = true;
            }
            break;
        }
    }
}

async function processQueue() {
    if (isProcessingQueue) return;
    isProcessingQueue = true;

    while (messageQueue.length > 0) {
        const msg = messageQueue.shift();
        await processMessage(msg);
    }

    isProcessingQueue = false;
}

self.onmessage = function(e) {
    messageQueue.push(e);
    processQueue();
};