Posts in category: Google AI

Posted by Long Zhao, Senior Research Scientist, and Ting Liu, Senior Staff Software Engineer, Google Research

An astounding number of videos are available on the Web, covering a variety of content from everyday moments people share to historical moments to scientific observations, each of which contains a unique record of the world. The right tools could help researchers analyze these videos, transforming how we understand the world around us.

Videos offer dynamic visual content far more rich than static images, capturing movement, changes, and dynamic relationships between entities. Analyzing this complexity, along with the immense diversity of publicly available video data, demands models that go beyond traditional image understanding. Consequently, many of the approaches that best perform on video understanding still rely on specialized models tailor-made for particular tasks. Recently, there has been exciting progress in this area using video foundation models (ViFMs), such as VideoCLIP, InternVideo, VideoCoCa, and UMT). However, building a ViFM that handles the sheer diversity of video data remains a challenge.

With the goal of building a single model for general-purpose video understanding, we introduced “VideoPrism: A Foundational Visual Encoder for Video Understanding”. VideoPrism is a ViFM designed to handle a wide spectrum of video understanding tasks, including classification, localization, retrieval, captioning, and question answering (QA). We propose innovations in both the pre-training data as well as the modeling strategy. We pre-train VideoPrism on a massive and diverse dataset: 36 million high-quality video-text pairs and 582 million video clips with noisy or machine-generated parallel text. Our pre-training approach is designed for this hybrid data, to learn both from video-text pairs and the videos themselves. VideoPrism is incredibly easy to adapt to new video understanding challenges, and achieves state-of-the-art performance using a single frozen model.

Pre-training data

A powerful ViFM needs a very large collection of videos on which to train — similar to other foundation models (FMs), such as those for large language models (LLMs). Ideally, we would want the pre-training data to be a representative sample of all the videos in the world. While naturally most of these videos do not have perfect captions or descriptions, even imperfect text can provide useful information about the semantic content of the video.

To give our model the best possible starting point, we put together a massive pre-training corpus consisting of several public and private datasets, including YT-Temporal-180M, InternVid, VideoCC, WTS-70M, etc. This includes 36 million carefully selected videos with high-quality captions, along with an additional 582 million clips with varying levels of noisy text (like auto-generated transcripts). To our knowledge, this is the largest and most diverse video training corpus of its kind.

Statistics on the video-text pre-training data. The large variations of the CLIP similarity scores (the higher, the better) demonstrate the diverse caption quality of our pre-training data, which is a byproduct of the various ways used to harvest the text.

Two-stage training

The VideoPrism model architecture stems from the standard vision transformer (ViT) with a factorized design that sequentially encodes spatial and temporal information following ViViT. Our training approach leverages both the high-quality video-text data and the video data with noisy text mentioned above. To start, we use contrastive learning (an approach that minimizes the distance between positive video-text pairs while maximizing the distance between negative video-text pairs) to teach our model to match videos with their own text descriptions, including imperfect ones. This builds a foundation for matching semantic language content to visual content.

After video-text contrastive training, we leverage the collection of videos without text descriptions. Here, we build on the masked video modeling framework to predict masked patches in a video, with a few improvements. We train the model to predict both the video-level global embedding and token-wise embeddings from the first-stage model to effectively leverage the knowledge acquired in that stage. We then randomly shuffle the predicted tokens to prevent the model from learning shortcuts.

What is unique about VideoPrism’s setup is that we use two complementary pre-training signals: text descriptions and the visual content within a video. Text descriptions often focus on what things look like, while the video content provides information about movement and visual dynamics. This enables VideoPrism to excel in tasks that demand an understanding of both appearance and motion.

Results

We conducted extensive evaluation on VideoPrism across four broad categories of video understanding tasks, including video classification and localization, video-text retrieval, video captioning, question answering, and scientific video understanding. VideoPrism achieves state-of-the-art performance on 30 out of 33 video understanding benchmarks — all with minimal adaptation of a single, frozen model.

VideoPrism compared to the previous best-performing FMs.

Classification and localization

We evaluate VideoPrism on an existing large-scale video understanding benchmark (VideoGLUE) covering classification and localization tasks. We found that (1) VideoPrism outperforms all of the other state-of-the-art FMs, and (2) no other single model consistently came in second place. This tells us that VideoPrism has learned to effectively pack a variety of video signals into one encoder — from semantics at different granularities to appearance and motion cues — and it works well across a variety of video sources.

VideoPrism outperforms state-of-the-art approaches (including CLIP, VATT, InternVideo, and UMT) on the video understanding benchmark. In this plot, we show the absolute score differences compared with the previous best model to highlight the relative improvements of VideoPrism. On Charades, ActivityNet, AVA, and AVA-K, we use mean average precision (mAP) as the evaluation metric. On the other datasets, we report top-1 accuracy.

Combining with LLMs

We further explore combining VideoPrism with LLMs to unlock its ability to handle various video-language tasks. In particular, when paired with a text encoder (following LiT) or a language decoder (such as PaLM-2), VideoPrism can be utilized for video-text retrieval, video captioning, and video QA tasks. We compare the combined models on a broad and challenging set of vision-language benchmarks. VideoPrism sets the new state of the art on most benchmarks. From the visual results, we find that VideoPrism is capable of understanding complex motions and appearances in videos (e.g., the model can recognize the different colors of spinning objects on the window in the visual examples below). These results demonstrate that VideoPrism is strongly compatible with language models.

VideoPrism achieves competitive results compared with state-of-the-art approaches (including VideoCoCa, UMT and Flamingo) on multiple video-text retrieval (top) and video captioning and video QA (bottom) benchmarks. We also show the absolute score differences compared with the previous best model to highlight the relative improvements of VideoPrism. We report the Recall@1 on MASRVTT, VATEX, and ActivityNet, CIDEr score on MSRVTT-Cap, VATEX-Cap, and YouCook2, top-1 accuracy on MSRVTT-QA and MSVD-QA, and WUPS index on NExT-QA.

Scientific applications

Finally, we tested VideoPrism on datasets used by scientists across domains, including fields such as ethology, behavioral neuroscience, and ecology. These datasets typically require domain expertise to annotate, for which we leverage existing scientific datasets open-sourced by the community including Fly vs. Fly, CalMS21, ChimpACT, and KABR. VideoPrism not only performs exceptionally well, but actually surpasses models designed specifically for those tasks. This suggests tools like VideoPrism have the potential to transform how scientists analyze video data across different fields.

VideoPrism outperforms the domain experts on various scientific benchmarks. We show the absolute score differences to highlight the relative improvements of VideoPrism. We report mean average precision (mAP) for all datasets, except for KABR which uses class-averaged top-1 accuracy.

Conclusion

With VideoPrism, we introduce a powerful and versatile video encoder that sets a new standard for general-purpose video understanding. Our emphasis on both building a massive and varied pre-training dataset and innovative modeling techniques has been validated through our extensive evaluations. Not only does VideoPrism consistently outperform strong baselines, but its unique ability to generalize positions it well for tackling an array of real-world applications. Because of its potential broad use, we are committed to continuing further responsible research in this space, guided by our AI Principles. We hope VideoPrism paves the way for future breakthroughs at the intersection of AI and video analysis, helping to realize the potential of ViFMs across domains such as scientific discovery, education, and healthcare.

Acknowledgements

This blog post is made on behalf of all the VideoPrism authors: Long Zhao, Nitesh B. Gundavarapu, Liangzhe Yuan, Hao Zhou, Shen Yan, Jennifer J. Sun, Luke Friedman, Rui Qian, Tobias Weyand, Yue Zhao, Rachel Hornung, Florian Schroff, Ming-Hsuan Yang, David A. Ross, Huisheng Wang, Hartwig Adam, Mikhail Sirotenko, Ting Liu, and Boqing Gong. We sincerely thank David Hendon for their product management efforts, and Alex Siegman, Ramya Ganeshan, and Victor Gomes for their program and resource management efforts. We also thank Hassan Akbari, Sherry Ben, Yoni Ben-Meshulam, Chun-Te Chu, Sam Clearwater, Yin Cui, Ilya Figotin, Anja Hauth, Sergey Ioffe, Xuhui Jia, Yeqing Li, Lu Jiang, Zu Kim, Dan Kondratyuk, Bill Mark, Arsha Nagrani, Caroline Pantofaru, Sushant Prakash, Cordelia Schmid, Bryan Seybold, Mojtaba Seyedhosseini, Amanda Sadler, Rif A. Saurous, Rachel Stigler, Paul Voigtlaender, Pingmei Xu, Chaochao Yan, Xuan Yang, and Yukun Zhu for the discussions, support, and feedback that greatly contributed to this work. We are grateful to Jay Yagnik, Rahul Sukthankar, and Tomas Izo for their enthusiastic support for this project. Lastly, we thank Tom Small, Jennifer J. Sun, Hao Zhou, Nitesh B. Gundavarapu, Luke Friedman, and Mikhail Sirotenko for the tremendous help with making this blog post.

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New improvements and AI-powered features are coming to Performance Max, including Gemini models for text generation.Read More

Posted by Zheng Xu, Research Scientist, and Yanxiang Zhang, Software Engineer, Google

Language models (LMs) trained to predict the next word given input text are the key technology for many applications [1, 2]. In Gboard, LMs are used to improve users’ typing experience by supporting features like next word prediction (NWP), Smart Compose, smart completion and suggestion, slide to type, and proofread. Deploying models on users’ devices rather than enterprise servers has advantages like lower latency and better privacy for model usage. While training on-device models directly from user data effectively improves the utility performance for applications such as NWP and smart text selection, protecting the privacy of user data for model training is important.

Gboard features powered by on-device language models.

In this blog we discuss how years of research advances now power the private training of Gboard LMs, since the proof-of-concept development of federated learning (FL) in 2017 and formal differential privacy (DP) guarantees in 2022. FL enables mobile phones to collaboratively learn a model while keeping all the training data on device, and DP provides a quantifiable measure of data anonymization. Formally, DP is often characterized by (ε, δ) with smaller values representing stronger guarantees. Machine learning (ML) models are considered to have reasonable DP guarantees for ε=10 and strong DP guarantees for ε=1 when δ is small.

As of today, all NWP neural network LMs in Gboard are trained with FL with formal DP guarantees, and all future launches of Gboard LMs trained on user data require DP. These 30+ Gboard on-device LMs are launched in 7+ languages and 15+ countries, and satisfy (ɛ, δ)-DP guarantees of small δ of 10^-10 and ɛ between 0.994 and 13.69. To the best of our knowledge, this is the largest known deployment of user-level DP in production at Google or anywhere, and the first time a strong DP guarantee of ɛ < 1 is announced for models trained directly on user data.

Privacy principles and practices in Gboard

In “Private Federated Learning in Gboard”, we discussed how different privacy principles are currently reflected in production models, including:

• Transparency and user control: We provide disclosure of what data is used, what purpose it is used for, how it is processed in various channels, and how Gboard users can easily configure the data usage in learning models.
• Data minimization: FL immediately aggregates only focused updates that improve a specific model. Secure aggregation (SecAgg) is an encryption method to further guarantee that only aggregated results of the ephemeral updates can be accessed.
• Data anonymization: DP is applied by the server to prevent models from memorizing the unique information in individual user’s training data.
• Auditability and verifiability: We have made public the key algorithmic approaches and privacy accounting in open-sourced code (TFF aggregator, TFP DPQuery, DP accounting, and FL system).

A brief history

In recent years, FL has become the default method for training Gboard on-device LMs from user data. In 2020, a DP mechanism that clips and adds noise to model updates was used to prevent memorization for training the Spanish LM in Spain, which satisfies finite DP guarantees (Tier 3 described in “How to DP-fy ML“ guide). In 2022, with the help of the DP-Follow-The-Regularized-Leader (DP-FTRL) algorithm, the Spanish LM became the first production neural network trained directly on user data announced with a formal DP guarantee of (ε=8.9, δ=10^-10)-DP (equivalent to the reported ρ=0.81 zero-Concentrated-Differential-Privacy), and therefore satisfies reasonable privacy guarantees (Tier 2).

Differential privacy by default in federated learning

In “Federated Learning of Gboard Language Models with Differential Privacy”, we announced that all the NWP neural network LMs in Gboard have DP guarantees, and all future launches of Gboard LMs trained on user data require DP guarantees. DP is enabled in FL by applying the following practices:

• Pre-train the model with the multilingual C4 dataset.
• Via simulation experiments on public datasets, find a large DP-noise-to-signal ratio that allows for high utility. Increasing the number of clients contributing to one round of model update improves privacy while keeping the noise ratio fixed for good utility, up to the point the DP target is met, or the maximum allowed by the system and the size of the population.
• Configure the parameter to restrict the frequency each client can contribute (e.g., once every few days) based on computation budget and estimated population in the FL system.
• Run DP-FTRL training with limits on the magnitude of per-device updates chosen either via adaptive clipping, or fixed based on experience.

SecAgg can be additionally applied by adopting the advances in improving computation and communication for scales and sensitivity.

Federated learning with differential privacy and (SecAgg).

Reporting DP guarantees

The DP guarantees of launched Gboard NWP LMs are visualized in the barplot below. The x-axis shows LMs labeled by language-locale and trained on corresponding populations; the y-axis shows the ε value when δ is fixed to a small value of 10^-10 for (ε, δ)-DP (lower is better). The utility of these models are either significantly better than previous non-neural models in production, or comparable with previous LMs without DP, measured based on user-interactions metrics during A/B testing. For example, by applying the best practices, the DP guarantee of the Spanish model in Spain is improved from ε=8.9 to ε=5.37. SecAgg is additionally used for training the Spanish model in Spain and English model in the US. More details of the DP guarantees are reported in the appendix following the guidelines outlined in “How to DP-fy ML”.

Towards stronger DP guarantees

The ε~10 DP guarantees of many launched LMs are already considered reasonable for ML models in practice, while the journey of DP FL in Gboard continues for improving user typing experience while protecting data privacy. We are excited to announce that, for the first time, production LMs of Portuguese in Brazil and Spanish in Latin America are trained and launched with a DP guarantee of ε ≤ 1, which satisfies Tier 1 strong privacy guarantees. Specifically, the (ε=0.994, δ=10^-10)-DP guarantee is achieved by running the advanced Matrix Factorization DP-FTRL (MF-DP-FTRL) algorithm, with 12,000+ devices participating in every training round of server model update larger than the common setting of 6500+ devices, and a carefully configured policy to restrict each client to at most participate twice in the total 2000 rounds of training in 14 days in the large Portuguese user population of Brazil. Using a similar setting, the es-US Spanish LM was trained in a large population combining multiple countries in Latin America to achieve (ε=0.994, δ=10^-10)-DP. The ε ≤ 1 es-US model significantly improved the utility in many countries, and launched in Colombia, Ecuador, Guatemala, Mexico, and Venezuela. For the smaller population in Spain, the DP guarantee of es-ES LM is improved from ε=5.37 to ε=3.42 by only replacing DP-FTRL with MF-DP-FTRL without increasing the number of devices participating every round. More technical details are disclosed in the colab for privacy accounting.

DP guarantees for Gboard NWP LMs (the purple bar represents the first es-ES launch of ε=8.9; cyan bars represent privacy improvements for models trained with MF-DP-FTRL; tiers are from “How to DP-fy ML“ guide; en-US* and es-ES* are additionally trained with SecAgg).

Discussion and next steps

Our experience suggests that DP can be achieved in practice through system algorithm co-design on client participation, and that both privacy and utility can be strong when populations are large and a large number of devices’ contributions are aggregated. Privacy-utility-computation trade-offs can be improved by using public data, the new MF-DP-FTRL algorithm, and tightening accounting. With these techniques, a strong DP guarantee of ε ≤ 1 is possible but still challenging. Active research on empirical privacy auditing [1, 2] suggests that DP models are potentially more private than the worst-case DP guarantees imply. While we keep pushing the frontier of algorithms, which dimension of privacy-utility-computation should be prioritized?

We are actively working on all privacy aspects of ML, including extending DP-FTRL to distributed DP and improving auditability and verifiability. Trusted Execution Environment opens the opportunity for substantially increasing the model size with verifiable privacy. The recent breakthrough in large LMs (LLMs) motivates us to rethink the usage of public information in private training and more future interactions between LLMs, on-device LMs, and Gboard production.

Acknowledgments

The authors would like to thank Peter Kairouz, Brendan McMahan, and Daniel Ramage for their early feedback on the blog post itself, Shaofeng Li and Tom Small for helping with the animated figures, and the teams at Google that helped with algorithm design, infrastructure implementation, and production maintenance. The collaborators below directly contribute to the presented results:

Research and algorithm development: Galen Andrew, Stanislav Chiknavaryan, Christopher A. Choquette-Choo, Arun Ganesh, Peter Kairouz, Ryan McKenna, H. Brendan McMahan, Jesse Rosenstock, Timon Van Overveldt, Keith Rush, Shuang Song, Thomas Steinke, Abhradeep Guha Thakurta, Om Thakkar, and Yuanbo Zhang.

Infrastructure, production and leadership support: Mingqing Chen, Stefan Dierauf, Billy Dou, Hubert Eichner, Zachary Garrett, Jeremy Gillula, Jianpeng Hou, Hui Li, Xu Liu, Wenzhi Mao, Brett McLarnon, Mengchen Pei, Daniel Ramage, Swaroop Ramaswamy, Haicheng Sun, Andreas Terzis, Yun Wang, Shanshan Wu, Yu Xiao, and Shumin Zhai.

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Posted by Nishant Jain, Pre-doctoral Researcher, and Pradeep Shenoy, Research Scientist, Google Research

The constantly changing nature of the world around us poses a significant challenge for the development of AI models. Often, models are trained on longitudinal data with the hope that the training data used will accurately represent inputs the model may receive in the future. More generally, the default assumption that all training data are equally relevant often breaks in practice. For example, the figure below shows images from the CLEAR nonstationary learning benchmark, and it illustrates how visual features of objects evolve significantly over a 10 year span (a phenomenon we refer to as slow concept drift), posing a challenge for object categorization models.

Sample images from the CLEAR benchmark. (Adapted from Lin et al.)

Alternative approaches, such as online and continual learning, repeatedly update a model with small amounts of recent data in order to keep it current. This implicitly prioritizes recent data, as the learnings from past data are gradually erased by subsequent updates. However in the real world, different kinds of information lose relevance at different rates, so there are two key issues: 1) By design they focus exclusively on the most recent data and lose any signal from older data that is erased. 2) Contributions from data instances decay uniformly over time irrespective of the contents of the data.

In our recent work, “Instance-Conditional Timescales of Decay for Non-Stationary Learning”, we propose to assign each instance an importance score during training in order to maximize model performance on future data. To accomplish this, we employ an auxiliary model that produces these scores using the training instance as well as its age. This model is jointly learned with the primary model. We address both the above challenges and achieve significant gains over other robust learning methods on a range of benchmark datasets for nonstationary learning. For instance, on a recent large-scale benchmark for nonstationary learning (~39M photos over a 10 year period), we show up to 15% relative accuracy gains through learned reweighting of training data.

The challenge of concept drift for supervised learning

To gain quantitative insight into slow concept drift, we built classifiers on a recent photo categorization task, comprising roughly 39M photographs sourced from social media websites over a 10 year period. We compared offline training, which iterated over all the training data multiple times in random order, and continual training, which iterated multiple times over each month of data in sequential (temporal) order. We measured model accuracy both during the training period and during a subsequent period where both models were frozen, i.e., not updated further on new data (shown below). At the end of the training period (left panel, x-axis = 0), both approaches have seen the same amount of data, but show a large performance gap. This is due to catastrophic forgetting, a problem in continual learning where a model’s knowledge of data from early on in the training sequence is diminished in an uncontrolled manner. On the other hand, forgetting has its advantages — over the test period (shown on the right), the continual trained model degrades much less rapidly than the offline model because it is less dependent on older data. The decay of both models’ accuracy in the test period is confirmation that the data is indeed evolving over time, and both models become increasingly less relevant.

Comparing offline and continually trained models on the photo classification task.

Time-sensitive reweighting of training data

We design a method combining the benefits of offline learning (the flexibility of effectively reusing all available data) and continual learning (the ability to downplay older data) to address slow concept drift. We build upon offline learning, then add careful control over the influence of past data and an optimization objective, both designed to reduce model decay in the future.

Suppose we wish to train a model, M, given some training data collected over time. We propose to also train a helper model that assigns a weight to each point based on its contents and age. This weight scales the contribution from that data point in the training objective for M. The objective of the weights is to improve the performance of M on future data.

In our work, we describe how the helper model can be meta-learned, i.e., learned alongside M in a manner that helps the learning of the model M itself. A key design choice of the helper model is that we separated out instance- and age-related contributions in a factored manner. Specifically, we set the weight by combining contributions from multiple different fixed timescales of decay, and learn an approximate “assignment” of a given instance to its most suited timescales. We find in our experiments that this form of the helper model outperforms many other alternatives we considered, ranging from unconstrained joint functions to a single timescale of decay (exponential or linear), due to its combination of simplicity and expressivity. Full details may be found in the paper.

Instance weight scoring

The top figure below shows that our learned helper model indeed up-weights more modern-looking objects in the CLEAR object recognition challenge; older-looking objects are correspondingly down-weighted. On closer examination (bottom figure below, gradient-based feature importance assessment), we see that the helper model focuses on the primary object within the image, as opposed to, e.g., background features that may spuriously be correlated with instance age.

Sample images from the CLEAR benchmark (camera & computer categories) assigned the highest and lowest weights respectively by our helper model.

Feature importance analysis of our helper model on sample images from the CLEAR benchmark.

Results

Gains on large-scale data

We first study the large-scale photo categorization task (PCAT) on the YFCC100M dataset discussed earlier, using the first five years of data for training and the next five years as test data. Our method (shown in red below) improves substantially over the no-reweighting baseline (black) as well as many other robust learning techniques. Interestingly, our method deliberately trades off accuracy on the distant past (training data unlikely to reoccur in the future) in exchange for marked improvements in the test period. Also, as desired, our method degrades less than other baselines in the test period.

Comparison of our method and relevant baselines on the PCAT dataset.

Broad applicability

We validated our findings on a wide range of nonstationary learning challenge datasets sourced from the academic literature (see 1, 2, 3, 4 for details) that spans data sources and modalities (photos, satellite images, social media text, medical records, sensor readings, tabular data) and sizes (ranging from 10k to 39M instances). We report significant gains in the test period when compared to the nearest published benchmark method for each dataset (shown below). Note that the previous best-known method may be different for each dataset. These results showcase the broad applicability of our approach.

Performance gain of our method on a variety of tasks studying natural concept drift. Our reported gains are over the previous best-known method for each dataset.

Extensions to continual learning

Finally, we consider an interesting extension of our work. The work above described how offline learning can be extended to handle concept drift using ideas inspired by continual learning. However, sometimes offline learning is infeasible — for example, if the amount of training data available is too large to maintain or process. We adapted our approach to continual learning in a straightforward manner by applying temporal reweighting within the context of each bucket of data being used to sequentially update the model. This proposal still retains some limitations of continual learning, e.g., model updates are performed only on most-recent data, and all optimization decisions (including our reweighting) are only made over that data. Nevertheless, our approach consistently beats regular continual learning as well as a wide range of other continual learning algorithms on the photo categorization benchmark (see below). Since our approach is complementary to the ideas in many baselines compared here, we anticipate even larger gains when combined with them.

Results of our method adapted to continual learning, compared to the latest baselines.

Conclusion

We addressed the challenge of data drift in learning by combining the strengths of previous approaches — offline learning with its effective reuse of data, and continual learning with its emphasis on more recent data. We hope that our work helps improve model robustness to concept drift in practice, and generates increased interest and new ideas in addressing the ubiquitous problem of slow concept drift.

Acknowledgements

We thank Mike Mozer for many interesting discussions in the early phase of this work, as well as very helpful advice and feedback during its development.

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