hltcoe/AGC_qwen2.5-vl_msrvtt

AGC-Qwen2.5-VL-3B

This model applies Attention-Guided Clustering (AGC) to compress multi-vector video representations for efficient ColBERT-style late interaction retrieval. Model weights are initialized from Qwen2.5-VL-3B-Instruct and finetuned on MSR-VTT for text-to-video retrieval with bidirectional attention.

AGC compresses ~1300 video token vectors into a fixed budget of 32 vectors (97.6% compression), while matching or exceeding uncompressed retrieval performance.

Method Overview

AGC consists of three components:

1. Attention-based Centroid Selection — Learned universal query tokens are appended to the document token sequence. The attention weights from these learned tokens to document tokens at the last transformer layer produce saliency scores, identifying the most semantically important regions. The top-m tokens by saliency are selected as cluster centroids.

2. Hard Clustering — Every document token is assigned to its nearest centroid via cosine similarity, grouping related content into coherent clusters while preserving distinct semantic details.

3. Weighted Aggregation — Tokens within each cluster are aggregated into a single vector using saliency-weighted averaging, prioritizing informative tokens and maintaining gradient flow stable for training.

The resulting m compressed vectors are used with ColBERT-style MaxSim scoring for retrieval.

Results on MSR-VTT

Method	Tokens	R@1	R@10	nDCG@10
OmniEmbed-7B	1	51.5	83.2	67.1
Video-ColBERT	26	51.5	85.5	67.7
Baseline (Ours, uncompressed)	1318	55.7	88.3	71.9
SeqResize	32	53.3	86.9	69.9
MemTok	32	54.2	86.4	69.9
H-Pool	32	54.1	87.3	70.4
AGC (This model)	32	56.9	87.0	71.5

AGC at 32 tokens outperforms the uncompressed baseline at R@1 while using only 2.4% of the original index size, demonstrating that compression reduces redundancy in multimodal representations.

Transferability Across Budgets

This model can also be evaluated at different token budgets without retraining:

Train Budget	Test Budget	R@1	R@10	nDCG@10
32	5	53.6	87.4	70.1
32	32	56.9	87.0	71.5
32	128	56.4	87.5	71.7

Model Details

Initial weights	Qwen2.5-VL-3B-Instruct
Architecture	Qwen2.5-VL with bidirectional attention
Hidden dimension	2048
Compression method	AGC (Attention-Guided Clustering)
Universal query tokens	32 learned universal query tokens (<|mem0|> – <|mem31|>)
Default budget	32 vectors per document
Scoring	ColBERT-style MaxSim (late interaction)
Normalization	L2-normalized embeddings
Query prefix	"Query: "
Passage prefix	"Passage: "
Precision	bfloat16
Training video frames	24

Usage

import torch
from transformers import AutoProcessor
from qwen_vl_utils import process_vision_info

from src.arguments import ModelArguments
from src.encoder.select_encoder import AttentionSelectEncoder
from src.models.qwen2_5_vl_embed.qwen2_5_vl_embed import Qwen2_5ForEmbedding
from src.utils import get_appending_token_strings

MODEL_ID = "hltcoe/AGC_qwen2.5-vl_msrvtt"
VIDEO_PATH = "PLACEHOLDER"
NUM_PROXY_TOKENS = 32
APPENDING_SUFFIX = "".join(get_appending_token_strings(NUM_PROXY_TOKENS))

# --- Setup ---
model_args = ModelArguments(
    model_name_or_path=MODEL_ID,
    pooling="select",
    normalize=True,
    num_appending_token=NUM_PROXY_TOKENS,
    use_cluster_pooling=True,
    use_attn_weight_cluster_pooling=True,
    attn_implementation="flash_attention_2",
)

processor = AutoProcessor.from_pretrained(MODEL_ID)
model = AttentionSelectEncoder.load(
    Qwen2_5ForEmbedding,
    model_args,
    attn_implementation=model_args.attn_implementation,
    dtype=torch.bfloat16,
)
model = model.to("cuda").eval()

# --- Encode a video document ---
passage_messages = [
    {
        "role": "user",
        "content": [
            {"type": "text", "text": "Passage: "},
            {"type": "video", "video": VIDEO_PATH, "nframes": 24, "max_pixels": 84672, "min_pixels": 75264},
        ],
    }
]
text = processor.apply_chat_template(passage_messages, tokenize=False, add_generation_prompt=False)
text += APPENDING_SUFFIX
image_inputs, video_inputs = process_vision_info(passage_messages)
passage_inputs = processor(
    text=[text], images=image_inputs, videos=video_inputs, padding=True, return_tensors="pt",
).to("cuda")

with torch.amp.autocast(device_type="cuda", dtype=torch.bfloat16):
    with torch.inference_mode():
        doc_embeddings, doc_mask = model.encode(passage_inputs, is_query=False)
        print(doc_embeddings.shape)
        # doc_embeddings: (1, 32, 2048) — 32 compressed AGC vectors

# --- Encode a text query ---
query_messages = [{"role": "user", "content": [{"type": "text", "text": "Query: a person is cooking"}]}]
query_text = processor.apply_chat_template(query_messages, tokenize=False, add_generation_prompt=False)
query_inputs = processor(text=[query_text], padding=True, return_tensors="pt").to("cuda")

with torch.amp.autocast(device_type="cuda", dtype=torch.bfloat16):
    with torch.inference_mode():
        query_embeddings, query_mask = model.encode(query_inputs, is_query=True)
        print(query_embeddings.shape)

# --- ColBERT MaxSim scoring ---
score = model.compute_similarity(query_embeddings, doc_embeddings, query_mask, doc_mask)
print(f"Similarity score: {score.item():.4f}")

Command line usage

For running inference and evaluation from the command line, see the Quick Start section.

Citation

@misc{qin2026multivectorindexcompressionmodality,
      title={Multi-Vector Index Compression in Any Modality}, 
      author={Hanxiang Qin and Alexander Martin and Rohan Jha and Chunsheng Zuo and Reno Kriz and Benjamin Van Durme},
      year={2026},
      eprint={2602.21202},
      archivePrefix={arXiv},
      primaryClass={cs.IR},
      url={https://arxiv.org/abs/2602.21202}, 
}