VideoLLM-MoD: Efficient Video-Language Streaming with Mixture-of-Depths Vision Computation

A well-known dilemma in large vision-language models (e.g., GPT-4, LLaVA) is that while increasing the number of vision tokens generally enhances visual understanding, it also significantly raises memory and computational costs, especially in long-term, dense video frame streaming scenarios. Although learnable approaches like Q-Former and Perceiver Resampler have been developed to reduce the vision token burden, they overlook the context causally modeled by LLMs (i.e., key-value cache), potentially leading to missed visual cues when addressing user queries. In this paper, we introduce a novel approach to reduce vision compute by leveraging redundant vision tokens"skipping layers"rather than decreasing the number of vision tokens. Our method, VideoLLM-MoD, is inspired by mixture-of-depths LLMs and addresses the challenge of numerous vision tokens in long-term or streaming video. Specifically, for each transformer layer, we learn to skip the computation for a high proportion (e.g., 80\%) of vision tokens, passing them directly to the next layer. This approach significantly enhances model efficiency, achieving approximately \textasciitilde42\% time and \textasciitilde30\% memory savings for the entire training. Moreover, our method reduces the computation in the context and avoid decreasing the vision tokens, thus preserving or even improving performance compared to the vanilla model. We conduct extensive experiments to demonstrate the effectiveness of VideoLLM-MoD, showing its state-of-the-art results on multiple benchmarks, including narration, forecasting, and summarization tasks in COIN, Ego4D, and Ego-Exo4D datasets.

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Peer review

Reviewer x5JZ4/10 · confidence 5/52024-07-10

Summary

This paper aims to comprehend long video streams with multi-modal large language models. The existing works use too few visual tokens to represent the video stream to guarantee efficiency but may sacrifice visual perception performance. The authors propose to keep more visual tokens to represent each video frame but only select the crucial visual tokens to pass the transformer decoder layers to reduce computation. The experiments show that the proposed mixture of depth architecture achieves a trade-off between the number of visual tokens and the computation efficiency.

Strengths

1. The explored problem is meaningful. Handling long videos with large language models is promising and has wide applications. 2. The motivation for using different depths of networks to process visual tokens is clear and makes sense. 3. The proposed method is simple and straightforward, and can effectively speed up the long video context processing without reducing the token number.

Weaknesses

1. The presentation of Section 3.1 and the Figure 6 are quite similar to VideoLLM-online [8]. And in Eq.1, why are the indicator and probability terms multiplied inside the logarithm? 2. The quantitative performance improvement over VideoLLM-online is quite marginal. And even the full computation only results in slight performance gains on some datasets. What is the underlying reason? Does it mean preserving very few visual tokens is sufficient? 3. Some visualizations are redundant, e.g., Figure 1 and Figure 5 are very similar. There lacks the visualization on the selected visual tokens in different layers. It is necessary to show the selection results to show what is crucial in the learned LayerExpert.

Questions

It is better to also compare with some video LLM works that compress each frame into fewer tokens, e.g., LLaMA-VID [33] in terms of both performance and efficiency.

Rating

4

Confidence

5

Soundness

2

Presentation

3

Contribution

2

Limitations

The authors have discussed the limitations in the lack of experiments on exocentric data.

Authorsrebuttal2024-08-12

Dear Reviewer x5JZ, We would like to express our sincere gratitude for the time and effort you spent reviewing our paper. As **the author reviewer discussion stage draws to a close**, we are eager for your response to ascertain if our detailed response has sufficiently addressed your concerns. We would be honored to address any further questions you may have. *We eagerly anticipate and highly value your re-evaluation of our paper.* Thank you once again for your thorough review of our paper. Best regards, Authors of Submission 10329

Reviewer 2CSB4/10 · confidence 4/52024-07-11

Summary

The document presents a novel approach called VideoLLM-MoD, which aims to efficiently scale up the vision resolution for online video large language models (VideoLLMs) without incurring high computational costs. The approach is inspired by the "mixture-of-depths" approach and learns to skip the computation for a high proportion of vision tokens. Experiments on several egocentric and instructional dataset show the method could achieve similar or even better performance with significantly less computation effort.

Strengths

1. the proposed method could reduce computational cost and save GPU memory, thus high vision resolution could be used for videoLLM. 2. lightweight LayerExpert is proposed to determine which vision tokens should be processed at certain layers. 3. streamingloss is proposed to ensure model remain silent when it has no necessary response.

Weaknesses

1. this proposal mostly borrow idea from "Mixture-of-Depths", the novel part is applying the idea to visual tokens. The original contributions may not be enough for top-tier conference. 2. experiments are mainly on egocentric and instructional datasets, lack of Diversity.

Questions

1. could authors summarize the original ideas or insights different from Mixture-of-Depths, except of different modalities?

Rating

4

Confidence

4

Soundness

2

Presentation

3

Contribution

2

Limitations

authors adequately addressed the limitations.

Authorsrebuttal2024-08-12

Dear Reviewer 2CSB, We would like to express our sincere gratitude for the time and effort you spent reviewing our paper. As **the author reviewer discussion stage draws to a close**, we are eager for your response to ascertain if our detailed response has sufficiently addressed your concerns. We would be honored to address any further questions you may have. *We eagerly anticipate and highly value your re-evaluation of our paper.* Thank you once again for your thorough review of our paper. Best regards, Authors of Submission 10329

Authorsrebuttal2024-08-14

Dear reviewer 2CSB: Thank you again for your thoughtful feedback! We hope the rebuttal and additional experiments we provided were helpful. If any residual concerns remain, we would be glad to discuss further. *If no concerns remain, we would appreciate it if you re-evaluate our paper.* Thank you once again for your thorough review of our paper. Best regards, Authors of Paper10329

Reviewer qExK5/10 · confidence 4/52024-07-12

Summary

This paper proposes a novel layer skipping approach to reduce the computation and memory consumption in modern vision-language models. The overall performance is good on several egocentric video understanding benchmarks.

Strengths

1. The proposed layer skipping strategy enables efficiient attention computation while retaining the performance. 2. Experimental results on mutliple online/offline benchmark datasets demonstrate the effectiveness of the method.

Weaknesses

1. This paper uses videollm-online as the baseline and merely proposes a weighted layer skipping strategy. The technical contribution of this method is relatively limited. 2. The discussion on the choice of LayerExpert is not fully discussed. The authors claimed that the proposed strategy can select critical visual tokens in the layer. It would be better if the authors include visualization results to prove this claim. In Table 3, are there any semantic-aware token selection strategies that can be used for comparison?

Questions

1. In Table 3, it is a little bit confusing why increasing the keep ratio r=0.3 results in worse performance? Also, it would be good to see the performance comparison on more keep ratios. 2. Could you please explain why the proposed method targets at online video processing? It seems that LayerExpert can be adapted to a variety of vision transformers and applied to many video understanding tasks, as proved in Table 4.

Rating

5

Confidence

4

Soundness

3

Presentation

3

Contribution

2

Limitations

Please refer to Weaknesses and Questions.

Authorsrebuttal2024-08-12

Dear Reviewer qExK, We would like to express our sincere gratitude for the time and effort you spent reviewing our paper. **As the author reviewer discussion stage draws to a close**, we are eager for your response to ascertain if our detailed response has sufficiently addressed your concerns. We would be honored to address any further questions you may have. Thank you once again for your thorough review of our paper. Best regards, Authors of Submission 10329

Authorsrebuttal2024-08-14

Dear reviewer qExK: Thank you again for your thoughtful feedback! We hope the rebuttal and additional experiments we provided were helpful. As the rebuttal period draws to a close, please don't hesitate to contact us if you have any problems. Thank you once again for your thorough review of our paper! Best regards, Authors of Paper10329

Reviewer HwD37/10 · confidence 4/52024-07-12

Summary

The core idea of this paper is to scaling up vision resolution for online video large language models. Instead of distributing FLOPs uniformly across all vision tokens in every decoder layer, they utilize a learnable module LayerExpert to allocate compute to critical vision tokens within the frame dynamically.

Strengths

Video being such a compute heavy workload, anything to do with temporal modeling if can be performed in a streaming fashion can enable several practical applications. Online video-llms are relatively unexplored, this paper proposes sparse vision encoder suitable for enabling streaming applications at the same time retain spatial resolution. The project is timely, the results are good. The results on 3 egocentric benchmarks show encouraging results.

Weaknesses

Not a major weakness; but performing experiments on ActivityNet-based training and evaluating on ViDSTG would give an idea of how does this MoD approach for making a sparse vision encoder work on standard benchmarks.

Questions

Will you make your code available for the community?

Rating

7

Confidence

4

Soundness

4

Presentation

4

Contribution

4

Limitations

The method does talk about increasing spatial resolution, but it doesn't consider spatial grounding. how does the author suggest the method can be extended for grounding?

Authorsrebuttal2024-08-12

Dear Reviewer HwD3, We would like to express our sincere gratitude for the time and effort you spent reviewing our paper. **As the author reviewer discussion stage draws to a close**, we are eager for your response to ascertain if our detailed response has sufficiently addressed your concerns. We would be honored to address any further questions you may have. Thank you once again for your thorough review of our paper. Best regards, Authors of Submission 10329

Authorsrebuttal2024-08-12

To all reviewers

Dear Reviewers, Thank you very much for your great effort in reviewing our paper. We sincerely appreciate your valuable and constructive feedback. The author/reviewer discussion stage will be ending soon. We are looking forward to your reply, to wonder whether our detailed response has adequately addressed your concerns. If you have further questions, we would be honored to address them. Thank you once again for reviewing our paper! Best regards, Authors of Paper10329

Reviewer x5JZ2024-08-12

Thanks for the author response. Some of my concerns still remain. The objective of MOD is to address the challenge of numerous vision tokens in long-term and streaming videos. However, the experiments are not convincing. + On the one hand, the current experiments on streaming long videos only show marginal improvements since they require no fine-grained information, failing to validate the effectiveness of proposed MOD. + On the other hand, the proposed MOD shows higher efficiency but comparable or even worse performance on some short video benchmarks compared to LLaMA-VID, which are not long enough to verify the effectiveness. I suggest the authors to include the results on some longer video benchmarks that require detailed understanding, such as EgoSchema [1], VideoMME [2] for evaluation. [1] Mangalam, Karttikeya, Raiymbek Akshulakov, and Jitendra Malik. "Egoschema: A diagnostic benchmark for very long-form video language understanding." Advances in Neural Information Processing Systems 36 (2024). [2] Fu, Chaoyou, et al. "Video-MME: The First-Ever Comprehensive Evaluation Benchmark of Multi-modal LLMs in Video Analysis." arXiv preprint arXiv:2405.21075 (2024).

Authorsrebuttal2024-08-13

Response to Reviewer x5JZ (1/2)

Thanks for your considerable feedback and suggestions! We argue that our approach **offers a general architecture that significantly reduces computational costs while maintaining performance for both training and inference in vision-language tasks**, *especially in scenarios that require processing a large number of vision tokens*, such as long-term, dense video frame online streaming. > On the one hand, the current experiments on streaming long videos only show marginal improvements since they require no fine-grained information, failing to validate the effectiveness of proposed MOD. 1. We validated the effectiveness of our approach on the *Video-MME[1]* benchmark. Our VideoLLM-MoD was trained using the same recipe as the initial submission paper, excluding the streaming loss, and with the same pretraining and finetuning data as LLaMA-VID[2]. Despite requiring significantly less training time—2.95x less than VideoLLaMA 2—our model still achieves top-tier performance, outperforming it. | Model | Frames | Training Cost | Overall(%) | Short Video(%) | Medium Video(%) | Long Video(%) | | ------------------ | ----------------------------- | ----------------- | ---------- | -------------- | --------------- | ------------- | | VideoLLaMA 2-7B | 32 frames && 32 tokens/frame | 65hrs & **2.95x** | 47.9 | 56.0 | 45.4 | 42.1 | | Chat-UniVi-v1.5-7B | 64 frames && 112 tokens/frame | 53hrs & **2.41x** | 40.6 | 45.7 | 40.3 | 35.8 | | Video-LLaVA-7B | 8 frames && 49 tokens/frame | 60hrs & **2.73x** | 39.9 | 45.3 | 38.0 | 36.2 | | VideoLLM-MoD-8B | 1fps && 10 tokens/frame | 22hrs | **49.2** | **58.4** | **46.6** | **42.4** | Given the limited time available during the discussion period, we will add experiments on EgoSchema[3] once our work is released. 2. Existing experiments on Ego4D narration benchmark can validate the effectiveness of our proposed approach. As *we claimed our core contribution is reduce both the training and inference cost without sacrificing the performance*, **we achieve comparable performance with 1.7x training speedup (24hrs -> 14hrs), 0.6x training FLOPs and 1.7x longer inference context (830s -> 1440s)**. Besides, as we claimed that in Paper Line 231-234, though the Full-computation in Paper Table 1 also shows marginal improvements, we found that larger vision resolution can indeed benefit performance, as shown in Figure 1, 5, and in experiments that demand more detailed visual information as shown in Table 4, 5. 3. Our approach allows for a larger visual budget within the same total computation, leading to significant performance gains from additional visual tokens, as demonstrated in extensive ablations in LLaVA-NEXT[4] and LongVA[5]. **Our method can be seen as a “free lunch” in increasing the vision resolution.** Moreover, **it is non-trivial to reduce computation in context under online video scenarios**, as online VideoLLMs must process every incoming visual token without relying on frame sampling or offline token merging, as done in Chat-UniVi [6]. We are the first to explore efficient vision modeling in context, rather than solely focusing on offline pruning or merging of vision tokens.

Authorsrebuttal2024-08-13

Response to Reviewer x5JZ (2/2)

> On the other hand, the proposed MOD shows higher efficiency but comparable or even worse performance on some short video benchmarks compared to LLaMA-VID, which are not long enough to verify the effectiveness. 1. It is worth noting that we used the same training recipe as LLaMA-VID during the previous rebuttal phase for a fair comparison. Our approach achieved comparable performance with significantly less training time and TFLOPs. However, our sparse architecture allows us to utilize far more visual tokens within the same computational budget. Specifically, we increased the number of visual tokens per frame (from CLS token + 1x1 average pooling to CLS token + 3x3 average pooling), **resulting in substantial performance gains due to the higher vision resolution. Remarkably, the total training cost remained at just 0.56x that of LLaMA-VID.** | Method | Training Cost (Pretrain + Finetune) && speedup | MSVD-QA | | MSRVTT-QA | | ActivityNet-QA | | Video-based Generative Performance | | | | | | :------------------------------------- | :--------------------------------------------- | :------- | :------ | :-------- | :------ | :------------- | :------ | ---------------------------------- | -------- | -------- | -------- | ----------- | | | | Acc | Score | Acc | Score | Acc | Score | Correctness | Detail | Context | Temporal | Consistency | | LLaMA-VID-7B | 9hrs + 30hrs | 69.7 | 3.7 | 57.7 | 3.2 | 47.4 | 3.3 | 2.96 | 3.00 | 3.53 | 2.46 | 2.51 | | VideoLLM-MoD-7B (1fps, 2tokens/frame) | 4hrs + 5.5hrs && **0.25x** | 68.5 | 3.7 | 58.2 | 3.3 | 46.3 | 3.2 | 2.88 | 2.98 | 3.41 | **2.51** | 2.50 | | VideoLLM-MoD-8B (1fps, 10tokens/frame) | 8hrs + 14hrs && **0.56x** | **78.5** | **3.9** | **65.3** | **3.6** | **53.4** | **3.4** | **3.12** | **3.16** | **3.75** | 2.44 | **3.65** | 2. We demonstrate that our method generalizes well across extensive benchmarks. Here is a summary: **4 Image Benchmarks:** GQA, MME, POPE, SQA **9 Video Benchmarks:** Ego4D Narration, Ego4D LTA, EgoExo4D Fine-grained Keystep Recognition, COIN, MSVD-QA, MSRVTT-QA, ActivityNet-QA, VideoChatGPT, Video-MME Thanks again for your feedback! We hope that our response can address your questions, and if you still have any concerns, we would be pleased to discuss them further with you. [1] Fu, Chaoyou, et al. "Video-MME: The First-Ever Comprehensive Evaluation Benchmark of Multi-modal LLMs in Video Analysis." arXiv preprint arXiv:2405.21075 (2024). [2] Li, Yanwei, et al. "LLaMA-VID: An Image is Worth 2 Tokens in Large Language Models." ECCV, 2024 [3] Mangalam, Karttikeya, Raiymbek Akshulakov, and Jitendra Malik. "Egoschema: A diagnostic benchmark for very long-form video language understanding." Neurips 2024. [4] Liu, Haotian, et al. "Llava-next: Improved reasoning, ocr, and world knowledge." (2024). [5] Zhang, Peiyuan, et al. "Long context transfer from language to vision." *arXiv preprint arXiv:2406.16852* (2024). [6] Jin, Peng, et al."Chat-UniVi: Unified Visual Representation Empowers Large Language Models with Image and Video Understanding." CVPR, 2024.

Authorsrebuttal2024-08-14

Dear reviewer x5JZ: Thank you again for your thoughtful feedback! We hope the rebuttal and additional experiments we provided were helpful. If any residual concerns remain, we would be glad to discuss further. *If no concerns remain, we would appreciate it if you re-evaluate our paper.* Thank you once again for your thorough review of our paper. Best regards, Authors of Paper10329

Authorsrebuttal2024-08-13

To all reviewers

Dear reviewers, As Reviewer x5JZ susggested, we further validate the effectiveness of our approach on the *Video-MME[1]* benchmark. Our VideoLLM-MoD was trained using the same recipe as the initial submission paper, excluding the streaming loss, and with the same pretraining and finetuning data as LLaMA-VID[2]. Despite requiring significantly less training time—2.95x less than VideoLLaMA 2—our model still achieves top-tier performance, outperforming it. | Model | Frames | Training Cost | Overall(%) | Short Video(%) | Medium Video(%) | Long Video(%) | | ------------------ | ----------------------------- | ----------------- | ---------- | -------------- | --------------- | ------------- | | VideoLLaMA 2-7B | 32 frames && 32 tokens/frame | 65hrs & **2.95x** | 47.9 | 56.0 | 45.4 | 42.1 | | Chat-UniVi-v1.5-7B | 64 frames && 112 tokens/frame | 53hrs & **2.41x** | 40.6 | 45.7 | 40.3 | 35.8 | | Video-LLaVA-7B | 8 frames && 49 tokens/frame | 60hrs & **2.73x** | 39.9 | 45.3 | 38.0 | 36.2 | | VideoLLM-MoD-8B | 1fps && 10 tokens/frame | 22hrs | **49.2** | **58.4** | **46.6** | **42.4** | [1] Fu, Chaoyou, et al. "Video-MME: The First-Ever Comprehensive Evaluation Benchmark of Multi-modal LLMs in Video Analysis." arXiv preprint arXiv:2405.21075 (2024). We hope that our response can address your questions. If you have any concerns, we would be pleased to discuss them further with you. Best regards, Authors of Paper10329

Program Chairsdecision2024-09-25

Decision

Accept (poster)

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