Add a script to detect alignement heads, usefull for distilled whisper

README.md

@@ -171,7 +171,8 @@ async def websocket_endpoint(websocket: WebSocket):
 | SimulStreaming backend options | Description | Default |
 |-----------|-------------|---------|
 | `--disable-fast-encoder` | Disable Faster Whisper or MLX Whisper backends for the encoder (if installed). Inference can be slower but helpful when GPU memory is limited | `False` |
-| `--custom-alignment-heads` | Use your own alignment heads, useful when `--model-dir` is used | `None` |
+| `--custom-alignment-heads` | Use your own alignment heads, useful when `--model-dir` is used. Use `scripts/determine_alignment_heads.py` to extract them. <img src="scripts/alignment_heads.png" alt="WhisperLiveKit Demo" width="300">
+ | `None` |
 | `--frame-threshold` | AlignAtt frame threshold (lower = faster, higher = more accurate) | `25` |
 | `--beams` | Number of beams for beam search (1 = greedy decoding) | `1` |
 | `--decoder` | Force decoder type (`beam` or `greedy`) | `auto` |

scripts/determine_alignment_heads.py

@@ -0,0 +1,292 @@
+"""Determine alignment heads for a variants, such as distilled model"""
+from __future__ import annotations
+
+import argparse
+import base64
+import gzip
+import io
+import pathlib
+import sys
+import math
+from typing import List, Optional, Sequence, Tuple, Union
+
+import numpy as np
+import torch
+from datasets import Audio as DatasetAudio, load_dataset
+import soundfile as sf
+import matplotlib.pyplot as plt
+REPO_ROOT = pathlib.Path(__file__).resolve().parents[1]
+WHISPER_ROOT = REPO_ROOT / "whisper"
+
+sys.path.insert(0, str(REPO_ROOT))
+sys.path.insert(0, str(WHISPER_ROOT))
+
+from whisper import load_model
+from whisper.audio import load_audio, log_mel_spectrogram, pad_or_trim
+from whisper.tokenizer import get_tokenizer
+
+AudioInput = Union[str, pathlib.Path, np.ndarray, torch.Tensor]
+
+
+def load_dataset_clips(name, config, split, limit):
+    ds = load_dataset(name, config, split=split)
+    ds = ds.cast_column("audio", DatasetAudio(decode=False))
+    clips = []
+    for idx, row in enumerate(ds):
+        if limit is not None and idx >= limit:
+            break
+        audio_field = row["audio"]
+        transcript = row["text"]
+
+        waveform_np, _ = sf.read(io.BytesIO(audio_field["bytes"]), dtype="float32")
+        if waveform_np.ndim > 1:
+            waveform_np = waveform_np.mean(axis=1)
+        waveform = waveform_np
+        transcript = str(transcript)
+
+        clips.append((waveform, transcript))
+    return clips
+
+
+def load_clips(args):
+    return load_dataset_clips(
+        args.dataset,
+        args.dataset_config,
+        args.dataset_split,
+        args.dataset_num_samples,
+    )
+
+
+def _waveform_from_source(source: AudioInput) -> torch.Tensor:
+    waveform = torch.from_numpy(source.astype(np.float32, copy=False))
+    return waveform
+
+
+def _parse_args():
+    parser = argparse.ArgumentParser()
+    parser.add_argument(
+        "--model",
+        type=str,
+        default="pytorch_model.bin",
+    )
+    parser.add_argument(
+        "--device",
+        type=str,
+        default="cuda" if torch.cuda.is_available() else "cpu",
+        help="Torch device to run on",
+    )
+    parser.add_argument(
+        "--dataset",
+        type=str,
+        default="librispeech_asr"
+    )
+    parser.add_argument(
+        "--dataset-config",
+        type=str,
+        default="clean" 
+    )
+    parser.add_argument(
+        "--dataset-split",
+        type=str,
+        default="validation[:1%]",
+    )
+    parser.add_argument(
+        "--dataset-num-samples",
+        type=int,
+        default=16,
+    )
+    parser.add_argument(
+        "--threshold",
+        type=float,
+        default=1.5,
+        help="Z score threshold for a head to be selected",
+    )
+    parser.add_argument(
+        "--votes",
+        type=float,
+        default=0.75,
+        help="percentage of clips that must vote for a head",
+    )
+    parser.add_argument(
+        "--output",
+        type=str,
+        default="alignment_heads.b85",
+    )
+    parser.add_argument(
+        "--visualize-top-k",
+        type=int,
+        default=32,
+    )
+    return parser.parse_args()
+
+
+def collect_heads(
+    model,
+    tokenizer,
+    clips: Sequence[Tuple[AudioInput, str]],
+    threshold: float,
+) -> Tuple[torch.Tensor, torch.Tensor]:
+    device = model.device
+    votes = torch.zeros(model.dims.n_text_layer, model.dims.n_text_head, device=device)
+    strengths = torch.zeros_like(votes)
+
+    for audio_source, transcript in clips:
+        waveform = pad_or_trim(_waveform_from_source(audio_source))
+        mel = log_mel_spectrogram(waveform, device=device)
+
+        tokens = torch.tensor(
+            [
+                *tokenizer.sot_sequence,
+                tokenizer.no_timestamps,
+                *tokenizer.encode(transcript),
+                tokenizer.eot,
+            ],
+            device=device,
+        )
+
+        qks = [None] * model.dims.n_text_layer
+        hooks = [
+            block.cross_attn.register_forward_hook(
+                lambda _, __, outputs, index=i: qks.__setitem__(index, outputs[-1][0])
+            )
+            for i, block in enumerate(model.decoder.blocks)
+        ]
+
+        with torch.no_grad():
+            model(mel.unsqueeze(0), tokens.unsqueeze(0))
+
+        for hook in hooks:
+            hook.remove()
+
+        for layer_idx, tensor in enumerate(qks):
+            if tensor is None:
+                continue
+            tensor = tensor[:, :, : mel.shape[-1] // 2]
+            tensor = tensor.softmax(dim=-1)
+            peak = tensor.max(dim=-1).values  # [heads, tokens]
+            strengths[layer_idx] += peak.mean(dim=-1)
+            zscore = (peak - peak.mean(dim=-1, keepdim=True)) / (
+                peak.std(dim=-1, keepdim=True, unbiased=False) + 1e-6
+            )
+            mask = (zscore > 3).any(dim=-1)
+            votes[layer_idx] += mask.float()
+
+    votes /= len(clips)
+    strengths /= len(clips)
+    return votes, strengths
+
+
+def _select_heads_for_visualization(selection, strengths, top_k):
+    selected = torch.nonzero(selection, as_tuple=False)
+    if selected.numel() == 0:
+        return []
+
+    entries = [
+        (int(layer.item()), int(head.item()), float(strengths[layer, head].item()))
+        for layer, head in selected
+    ]
+    entries.sort(key=lambda item: item[2], reverse=True)
+    return entries[:top_k]
+
+def _extract_heatmaps(
+    model,
+    tokenizer,
+    clip: Tuple[AudioInput, str],
+    heads: Sequence[Tuple[int, int, float]],
+) -> dict:
+    if not heads:
+        return {}
+
+    target_map = {}
+    for layer, head, _ in heads:
+        target_map.setdefault(layer, set()).add(head)
+
+    waveform = pad_or_trim(_waveform_from_source(clip[0]))
+    mel = log_mel_spectrogram(waveform, device=model.device)
+    transcript = clip[1]
+    tokens = torch.tensor(
+        [
+            *tokenizer.sot_sequence,
+            tokenizer.no_timestamps,
+            *tokenizer.encode(transcript),
+            tokenizer.eot,
+        ],
+        device=model.device,
+    )
+
+    QKs = [None] * model.dims.n_text_layer
+    hooks = [
+        block.cross_attn.register_forward_hook(
+            lambda _, __, outputs, index=i: QKs.__setitem__(index, outputs[-1][0])
+        )
+        for i, block in enumerate(model.decoder.blocks)
+    ]
+
+    with torch.no_grad():
+        model(mel.unsqueeze(0), tokens.unsqueeze(0))
+
+    for hook in hooks:
+        hook.remove()
+
+    heatmaps = {}
+    for layer_idx, tensor in enumerate(QKs):
+        if tensor is None or layer_idx not in target_map:
+            continue
+        tensor = tensor[:, :, : mel.shape[-1] // 2]
+        tensor = tensor.softmax(dim=-1).cpu()
+        for head_idx in target_map[layer_idx]:
+            heatmaps[(layer_idx, head_idx)] = tensor[head_idx]
+
+    return heatmaps
+
+
+def _plot_heatmaps(
+    heads, heatmaps, output_path):
+    cols = min(3, len(heads))
+    rows = math.ceil(len(heads) / cols)
+    fig, axes = plt.subplots(rows, cols, figsize=(4 * cols, 3.2 * rows), squeeze=False)
+
+    for idx, (layer, head, score) in enumerate(heads):
+        ax = axes[idx // cols][idx % cols]
+        mat = heatmaps.get((layer, head))
+        if mat is None:
+            ax.axis("off")
+            continue
+        im = ax.imshow(mat.to(torch.float32).numpy(), aspect="auto", origin="lower")
+        ax.set_title(f"L{layer} H{head} · score {score:.2f}")
+        ax.set_xlabel("time")
+        ax.set_ylabel("tokens")
+
+    for j in range(len(heads), rows * cols):
+        axes[j // cols][j % cols].axis("off")
+
+    fig.tight_layout()
+    fig.savefig(output_path, dpi=200)
+    plt.close(fig)
+
+
+def _dump_mask(mask: torch.Tensor, output_path: str):
+    payload = mask.numpy().astype(np.bool_)
+    blob = base64.b85encode(gzip.compress(payload.tobytes()))
+    with open(output_path, "wb") as f:
+        f.write(blob)
+
+
+def main():
+    args = _parse_args()
+    model = load_model(args.model, device=args.device)
+    model.eval()
+    tokenizer = get_tokenizer(multilingual=model.is_multilingual)
+    clips = load_clips(args)
+
+    votes, strengths = collect_heads(model, tokenizer, clips, args.threshold)
+    # selection = votes > 0.5
+    selection = strengths > 0.05
+    _dump_mask(selection.cpu(), args.output)
+
+    viz_heads = _select_heads_for_visualization(selection, strengths, args.visualize_top_k)
+    heatmaps = _extract_heatmaps(model, tokenizer, clips[0], viz_heads)
+    _plot_heatmaps(viz_heads, heatmaps, "alignment_heads.png")
+
+if __name__ == "__main__":
+    main()

scripts/sync_extension.py

@@ -1,9 +1,10 @@
+"""Copy core files from web directory to Chrome extension directory."""
+
 import shutil
 import os
 from pathlib import Path
 
 def sync_extension_files():
-    """Copy core files from web directory to Chrome extension directory."""
     
     web_dir = Path("whisperlivekit/web")
     extension_dir = Path("chrome-extension")

whisperlivekit/simul_whisper/backend.py

@@ -195,7 +195,6 @@ class SimulStreamingASR():
                 'large-v3': './large-v3.pt',
                 'large': './large-v3.pt'
             }
-            self.pt_path = Path(model_mapping.get(self.model_size, f'./{self.model_size}.pt'))
             self.model_name = self.model_size
             is_multilingual = not self.model_name.endswith(".en")