A compact multimodal embedding model that unifies text, image, and audio representations in a shared semantic space. Part of the MoM (Mixture of Models) family.

Model Description

multi-modal-embed-small is a lightweight multimodal encoder (~120M parameters) supporting:

Text encoding via MiniLM-L6-v2 (22M params)
Image encoding via SigLIP-base-patch16-512 (86M params)
Audio encoding via Whisper-tiny encoder (8M params)
Cross-modal fusion via 2-layer transformer attention
2DMSE: Two-Dimensional Matryoshka Sentence Embeddings for adaptive compute
MRL: Matryoshka Representation Learning for flexible embedding dimensions

Key Features

Feature	Description
Embedding Dimension	384 (supports MRL truncation to 32, 64, 128, 256)
Image Resolution	512×512
Audio Input	Up to 30s, 16kHz (Whisper Mel spectrogram)
Modalities	Text, Image, Audio, Multimodal fusion
2DMSE Support	Early exit at any encoder layer
Languages	English

Installation

pip install torch transformers pillow safetensors

Usage

Load Model

Two checkpoint formats are available:

model.pt (932 MB) - PyTorch format
model.safetensors (1.35 GB) - SafeTensors format

python

import torch
import torch.nn as nn
import torch.nn.functional as F
from transformers import AutoModel, AutoTokenizer, SiglipModel, SiglipProcessor, WhisperModel, WhisperFeatureExtractor
from huggingface_hub import hf_hub_download

class MultiModalEmbedder(nn.Module):
    """Standalone multimodal embedder - no external dependencies."""
    
    def __init__(self):
        super().__init__()
        # Text encoder (384d, no projection needed)
        self.text_tokenizer = AutoTokenizer.from_pretrained("sentence-transformers/all-MiniLM-L6-v2")
        self.text_encoder = AutoModel.from_pretrained("sentence-transformers/all-MiniLM-L6-v2")
        
        # Image encoder (768d -> 384d projection)
        self.image_processor = SiglipProcessor.from_pretrained("google/siglip-base-patch16-512")
        self.image_encoder = SiglipModel.from_pretrained("google/siglip-base-patch16-512").vision_model
        self.image_proj = nn.Linear(768, 384)
        
        # Audio encoder (384d, no projection needed)
        self.audio_processor = WhisperFeatureExtractor.from_pretrained("openai/whisper-tiny")
        self.audio_encoder = WhisperModel.from_pretrained("openai/whisper-tiny").encoder
    
    def encode_text(self, texts):
        if isinstance(texts, str):
            texts = [texts]
        inputs = self.text_tokenizer(texts, padding=True, truncation=True, return_tensors="pt")
        inputs = {k: v.to(next(self.parameters()).device) for k, v in inputs.items()}
        outputs = self.text_encoder(**inputs)
        embeddings = outputs.last_hidden_state.mean(dim=1)  # Mean pooling
        return F.normalize(embeddings, p=2, dim=-1)
    
    def encode_image(self, images):
        inputs = self.image_processor(images=images, return_tensors="pt")
        inputs = {k: v.to(next(self.parameters()).device) for k, v in inputs.items()}
        outputs = self.image_encoder(**inputs)
        embeddings = outputs.pooler_output
        embeddings = self.image_proj(embeddings)  # 768 -> 384
        return F.normalize(embeddings, p=2, dim=-1)
    
    def encode_audio(self, waveform):
        # waveform: numpy array or tensor at 16kHz
        if isinstance(waveform, torch.Tensor):
            waveform = waveform.squeeze().numpy()
        inputs = self.audio_processor(waveform, sampling_rate=16000, return_tensors="pt")
        inputs = {k: v.to(next(self.parameters()).device) for k, v in inputs.items()}
        outputs = self.audio_encoder(**inputs)
        embeddings = outputs.last_hidden_state.mean(dim=1)  # Mean pooling
        return F.normalize(embeddings, p=2, dim=-1)

# Load model
model = MultiModalEmbedder()

# Download and load trained weights
checkpoint_path = hf_hub_download(
    repo_id="llm-semantic-router/multi-modal-embed-small",
    filename="model.pt"
)
state_dict = torch.load(checkpoint_path, map_location="cpu", weights_only=False)

# Load text encoder weights
model.text_encoder.load_state_dict({
    k.replace("text_encoder.encoder.", ""): v 
    for k, v in state_dict.items() 
    if k.startswith("text_encoder.encoder.")
})

# Load image encoder and projection weights
model.image_encoder.load_state_dict({
    k.replace("image_encoder.vision_encoder.", ""): v 
    for k, v in state_dict.items() 
    if k.startswith("image_encoder.vision_encoder.")
})
model.image_proj.load_state_dict({
    k.replace("image_encoder.projection.", ""): v 
    for k, v in state_dict.items() 
    if k.startswith("image_encoder.projection.")
})

# Load audio encoder weights
model.audio_encoder.load_state_dict({
    k.replace("audio_encoder.encoder.", ""): v 
    for k, v in state_dict.items() 
    if k.startswith("audio_encoder.encoder.")
})

model.eval()
print("Model loaded successfully!")

Text Embedding

python

import torch.nn.functional as F

# Single text
text_embedding = model.encode_text("A photo of a cat")  # Shape: [1, 384]

# Batch of texts
texts = ["A fluffy orange cat", "A golden retriever dog", "A red sports car"]
text_embeddings = model.encode_text(texts)  # Shape: [3, 384]

# Compute similarity
similarities = F.cosine_similarity(text_embeddings[0:1], text_embeddings[1:], dim=-1)
print(f"Cat vs Dog: {similarities[0]:.3f}")
print(f"Cat vs Car: {similarities[1]:.3f}")

Image Embedding

python

from PIL import Image
import requests
from io import BytesIO

# Load image
url = "https://upload.wikimedia.org/wikipedia/commons/thumb/3/3a/Cat03.jpg/1200px-Cat03.jpg"
image = Image.open(BytesIO(requests.get(url).content)).convert('RGB')

# Get embedding
image_embedding = model.encode_image(image)  # Shape: [1, 384]

Audio Embedding

python

import torchaudio

# Load audio (16kHz)
waveform, sample_rate = torchaudio.load("speech.wav")
if sample_rate != 16000:
    waveform = torchaudio.functional.resample(waveform, sample_rate, 16000)

# Get embedding
audio_embedding = model.encode_audio(waveform)  # Shape: [1, 384]

Cross-Modal Retrieval

python

# Image-to-text retrieval
image = Image.open("cat.jpg").convert('RGB')
image_emb = model.encode_image(image)

captions = [
    "A cat sleeping on a bed",
    "A dog playing in the park",
    "A car driving on the highway",
]
text_embs = model.encode_text(captions)

similarities = F.cosine_similarity(image_emb, text_embs)
best_idx = similarities.argmax().item()
print(f"Best match: {captions[best_idx]} ({similarities[best_idx]:.3f})")

Matryoshka Dimension Reduction

python

# Full 384-dim embedding
full_emb = model.encode_text("Hello world")  # [1, 384]

# Truncate to smaller dimensions
emb_256 = F.normalize(full_emb[:, :256], p=2, dim=-1)  # 1.5x faster retrieval
emb_128 = F.normalize(full_emb[:, :128], p=2, dim=-1)  # 3x faster retrieval
emb_64 = F.normalize(full_emb[:, :64], p=2, dim=-1)    # 6x faster retrieval

Architecture

┌──────────────────────────────────────────────────────────────┐
│                  multi-modal-embed-small                     │
├──────────────────────────────────────────────────────────────┤
│  Text Encoder:  MiniLM-L6-v2           (22M params, 6 layers)│
│  Image Encoder: SigLIP-base-patch16-512 (86M params)         │
│  Audio Encoder: Whisper-tiny encoder    (8M params, 4 layers) │
│  Fusion:        2-layer Transformer                          │
├──────────────────────────────────────────────────────────────┤
│  Output: 384-dim normalized embeddings                       │
│  2DMSE:  Layer 0-5 early exit support                        │
│  MRL:    32, 64, 128, 256, 384 dim truncation                │
└──────────────────────────────────────────────────────────────┘

Training

Training Data

Modality	Dataset	Samples	Purpose
Image-Text	LLaVA-CC3M	595K	Image-text alignment
Image-Text	COCO Captions	25K	Validation
Audio-Text	LibriSpeech	105K	Audio-text alignment

Training Stages

Stage	Description	Trainable	Epochs
1	Initial alignment	Projection layers only	6
2	Partial unfreeze	Top encoder layers + projections	3
4	Full image-text	All image/text parameters	3
5	Audio alignment	Audio encoder (text/image frozen)	5

Training Configuration

Hardware: 8× AMD MI300X GPUs
Precision: BF16 mixed precision
Batch Size: 64 per GPU (512 effective)
Optimizer: AdamW
Learning Rate: 1e-4 → 5e-5 (stage dependent)
Loss: InfoNCE contrastive + Matryoshka loss

Evaluation

Image-Text Retrieval (COCO Validation)

Metric	Image→Text	Text→Image
R@1	41.88%	39.21%
R@5	71.64%	69.15%
R@10	82.16%	80.02%

Audio-Text Retrieval (LibriSpeech)

Metric	Audio→Text
R@1	36.38%
R@5	68.22%
R@10	79.52%

MRL Quality Retention

Dimension	Compression	Quality
384 (full)	1×	100%
256	1.5×	~98%
128	3×	~95%
64	6×	~90%

Limitations

English language only
Image resolution fixed at 512×512
Audio limited to 30 seconds
Best for retrieval/similarity, not generation

Citation

bibtex

@misc{multi-modal-embed-small-2026,
  title={multi-modal-embed-small: Compact Multimodal Embeddings with 2DMSE},
  author={Semantic Router Team},
  year={2026},
  url={https://huggingface.co/llm-semantic-router/multi-modal-embed-small}
}

License

Apache 2.0