TRACE: Temporal Grounding Video LLM via Causal Event Modeling
Yongxin GuoJingyu LiuMingda LiQingbin LiuXi ChenXiaoying Tang
Proposes TRACE, a task-interleaved video language model that advances video temporal grounding by formulating predictions as causal event sequences combining timestamps, saliency scores, and captions rather than relying solely on text generation.
Video temporal grounding is essential for downstream applications such as automated video editing, content summarization, and moment retrieval. While modern video-based large language models have shown promise in handling multiple tasks without task-specific retraining, they traditionally rely purely on unstructured text generation. This reliance creates a mismatch with the natural structure of video data, which depends fundamentally on explicit timestamps and saliency scores alongside descriptions. As a result, existing models struggle to pinpoint precise event timings and assess moment importance accurately.
To address this limitation, the article presents a causal event modeling framework and develops a task-interleaved model named TRACE. Instead of treating video interpretation as pure narrative text, the model formalizes outputs as structured event triplets composed of timestamps, saliency scores, and textual descriptions. The primary objective is to evaluate whether structuring model outputs to mirror video temporality enables a unified model to achieve state-of-the-art accuracy across diverse temporal grounding tasks without losing broad language and reasoning capabilities.
The framework implements dedicated encoders and decoding heads to handle visual frames, timestamps, scores, and text separately, cycling between them using special synchronization tokens. This approach prevents numerical time and score data from corrupting the core text model's learned knowledge base. Training is executed in two stages across roughly two million samples spanning instruction tuning, video captioning, and question-answering datasets. Model evaluation focuses on standard benchmarks including YouCook2 for dense video captioning, Charades-STA for moment retrieval, and QVHighlights for highlight detection.
Empirical evaluations demonstrate substantial performance gains over existing temporal grounding and traditional video language models. In zero-shot testing, TRACE improves captioning quality and timing alignment on YouCook2, raising CIDEr scores by 3.1 points and F1 scores by 4.9%. On moment retrieval via Charades-STA, recall increases by 6.5% at an intersection-over-union threshold of 0.5. For highlight detection on QVHighlights, the model achieves a 10.3% boost in mean average precision and a 9.2% increase in top-ranked hit rate. Moreover, ablation tests show that omitting the independent task encoders and decoding heads causes instruction-following to collapse, proving the necessity of decoupled task processing. When fine-tuned, TRACE matches or exceeds non-generative, single-purpose baseline models while retaining generalist versatility.
These findings suggest that aligning model architecture with intrinsic video structure substantially improves temporal reasoning efficiency and precision. Organizations developing video analytics, content moderation, or media asset management systems can deploy unified foundational models rather than maintaining fragmented, task-specific pipelines. This consolidation reduces operational complexity, lower deployment costs, and improves zero-shot retrieval in large video repositories without requiring costly specialized fine-tuning for each new scenario.
Future development should focus on integrating explicit causality discovery mechanisms and causal graphs into the input prompts to help the model capture complex inter-event dependencies beyond standard left-to-right temporal sequences. Additionally, training data should be expanded to include timestamped question-and-answer pairs to bolster contextual reasoning. Practitioners adopting this approach should note that performance depends heavily on the accuracy of training annotations; incorporating broad datasets with noisy boundaries can slightly degrade precision on short-video tasks. Nonetheless, the architecture provides strong, highly reliable improvements across standard video understanding benchmarks.
- Paper: TR-DETR: Task-Reciprocal Transformer for Joint Moment Retrieval and Highlight Detection, Hao Sun et al. (2024). Understanding how moment retrieval and highlight detection can be modeled jointly provides essential context for TRACE's unified event-triplet formulation and benchmark evaluations.
- Paper: Dense-Captioning Events in Videos, Ranjay Krishna et al. (2017). This foundational paper establishes dense video captioning and event localization with timestamps, forming the core temporal grounding formulation that TRACE builds upon.
- Paper: Compositional Temporal Grounding with Structured Variational Cross-Graph Correspondence Learning, Juncheng Li et al. (2022). This work explores structural and compositional aspects of video temporal grounding, highlighting the limitations of unstructured text mapping that TRACE explicitly addresses.
- Paper: Video-ChatGPT: Towards Detailed Video Understanding via Large Vision and Language Models, Muhammad Maaz et al. (2023). Familiarity with early conversational video large language models illustrates the baseline text-only generative paradigms that TRACE seeks to improve with structured causal event modeling.
- Paper: Video-LLaVA: Learning United Visual Representation by Alignment Before Projection, Bin Lin et al. (2023). Examining unified visual representations across video-LLMs clarifies the underlying multimodal architecture patterns adapted and decoupled in TRACE.
- Paper: TimeSuite: Improving MLLMs for Long Video Understanding via Grounded Tuning, Xiangyu Zeng 0004 et al. (2025). TimeSuite builds on temporal grounding in multimodal LLMs by introducing grounded tuning and specialized position encodings to handle long-form video reasoning.
- Paper: Adaptive Keyframe Sampling for Long Video Understanding, Xi Tang et al. (2025). Adaptive Keyframe Sampling complements structured temporal grounding models like TRACE by dynamically selecting informative frames to enhance long video comprehension.
- Paper: M-LLM Based Video Frame Selection for Efficient Video Understanding, Kai Hu 0010 et al. (2025). This work extends efficient video understanding principles by using an M-LLM frame selector to optimize visual context for downstream temporal reasoning tasks.
