Data Science

How Netflix Uses ML & AI For Better Recommendation for Users

Published: 12th April, 2023

Harshini Bhat

Data Science Consultant at almaBetter

Explores how Netflix leverages the power of machine learning (ML) to keep users engaged through personalized recommendations to content optimization.

Imagine having a personal assistant who knows your taste in movies and TV shows better than anyone else. A virtual buddy who can recommend exactly what you want to watch, when you want to watch it. That's what Netflix's Machine Learning algorithm provides to its millions of users around the world. By analyzing your viewing history, preferences, and behavior, it can predict what content you will love and serve it to you.

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Let’s deep dive and find out more about how Netflix uses Machine Learning at its best to optimize its operations and artificial intelligence to satisfy its customer base.

The evolution of ML fact store: The backbone of Netflix's recommendation system

Netflix has become a household name when it comes to entertainment streaming services. It has revolutionized the way we consume content and set new standards in the industry using Machine Learning. ML algorithms can only be as good as the data that is provided to them. That is where Axion, Netflix's fact store, comes into play. Axion is an integral part of Netflix's ML platform that serves Machine Learning needs across the company. Its primary purpose is to provide high-quality data to compute applications, which generate personalized recommendations for Netflix's members. By using Axion, Netflix aims to remove any training-serving skew and make offline experimentation faster.

Axion is a fact store that stores data about members and videos. Axion interacts with various components of Netflix's ML platform to generate personalized recommendations for members. Compute applications fetch facts from respective data services, run feature encoders to generate features and score the ML models to generate recommendations. Offline feature generators regenerate the values of the features that were generated for inferencing in the computing application. These generators are powered by spark applications that enable on-demand feature generation using new, existing, or updated feature encoders.

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One of the key advantages of using Axion is that feature encoders are shared between compute applications and offline feature generators. This ensures that there is no training/serving skew as the same data and code are used for both online and offline feature generation.

Over the years, Axion's design has evolved, but the current design limits storing a map per row, which creates a limitation when a compute application needs to log multiple values for the same key. Netflix is continuously working to optimize it so that it can continue to provide personalized recommendations that match its members' interests and set new standards in the entertainment industry.

Check out our latest blog "Netflix Churn Rate Prediction Case Study"

Providing high-fidelity, real-time data with Flink for Machine Learning at Netflix

The data generated by Netflix's streaming platform is massive. This data must be processed in real-time in order to deliver customized recommendations. Netflix employs Apache Flink, an open-source platform, to broadcast this data and ensure that it is available in real-time.

Apache Flink is a framework that processes stream data in real-time and is used by Netflix for real-time data pipelines. It is also used for batch processing and generating features for offline ML models. Netflix checks data for correctness before processing it with ML algorithms using a validation framework built on Flink. Flink also handles backpressure, ensuring no data loss and stability under heavy load. Apache Flink provides real-time processing capabilities that are essential for Netflix's data pipelines, which need to process millions of data points per second

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Netflix has built a validation framework on top of Flink. This validation framework ensures that only high-quality, error-free data is fed into the ML models. This approach ensures that Netflix delivers accurate recommendations to its members, which ultimately results in increased user engagement and retention. Hence, Apache Flink has become a critical component in Netflix's data ecosystem, providing real-time processing capabilities and ensuring data quality and correctness before feeding it into ML models.

To learn more check out our latest MLOPs Tutorial.

Using Machine Learning to improve streaming quality at Netflix

Netflix uses Machine Learning techniques to optimize various aspects of the streaming process. These include video quality adaptation during playback, predictive caching, network quality characterization and prediction, and device anomaly detection.

Video quality adaptation during playback is critical in ensuring users have a smooth and enjoyable experience. Netflix uses adaptive streaming algorithms to select the video quality that will optimize the quality of experience for the user. This involves choosing which video quality to stream based on current network and device conditions and can be measured in several ways, including initial wait time, overall video quality, rebuffering frequency, and perceptible fluctuations in quality during playback.

Predictive caching is another area where statistical models can improve the streaming experience. By predicting what a user is likely to play next, Netflix can cache (part of) it on the device before the user hits play, enabling the video to start faster and/or at a higher quality. This involves combining various aspects of a user's viewing history with recent interactions and other contextual variables to formulate a supervised learning problem that maximizes the likelihood of catching what the user actually ended up playing.

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Network quality characterization and prediction are also essential for delivering high-quality streaming experiences. Netflix has found that network quality is difficult to characterize and predict due to factors such as stability and predictability. It uses Machine Learning to predict the network throughout, based on historical data. This information can then be used to adapt video quality during playback.

Device anomaly detection is a crucial aspect of this process, as Netflix operates on over a thousand different types of devices, each with its own unique features and firmware updates. When a device undergoes an update, it can sometimes cause a problem for the user experience, such as an app not starting up correctly or playback being inhibited or degraded somehow. By analyzing the historical data on alerts triggered in the past and the ultimate determination made by a human, a model can be trained to predict the likelihood that a given set of measured conditions constitutes a real problem. This helps the device reliability team to focus on the real problems instead of spending time investigating false positives.

Bias-Variance Decomposition for Ranking

Netflix's ranking algorithm achieves personalization and at scale by using a bias-variance decomposition technique to optimize the tradeoff between bias and variance. The algorithm breaks down the ranking problem into two separate components: a bias component that captures general trends in the data, and a variance component that captures the unique preferences of each user.

The bias component is generated by training a model on a large dataset of user interactions with the Netflix library, capturing general trends such as the popularity of certain genres or the influence of a particular actor on a movie's success. The variance component is generated by training a separate model for each user based on their viewing history, capturing their unique preferences.

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By combining the bias and variance components, Netflix's ranking algorithm generates personalized recommendations that take into account both general trends and unique user preferences. The bias-variance decomposition technique provides a way to balance the complexity of the model with its ability to generalize to new data, optimizing the tradeoff between bias and variance. This enables Netflix to tailor recommendations to individual users while still capturing general trends and patterns in the data.

Netflix AI Recommendations

Netflix's AI recommendation algorithm, called Cinematch, is a Machine Learning algorithm that uses a combination of collaborative filtering and content-based filtering techniques to generate personalized recommendations for its users. It analyzes users viewing histories, ratings, and other data to identify patterns of user behavior and preferences. It also uses metadata such as genre, director, and cast information to identify similarities between different movies or TV shows.

Additionally, Netflix uses Deep Learning algorithms to analyze images and audio, which helps the system to understand better and categorize the content. Through continuous A/B testing and updates, Netflix's recommendation algorithm has evolved over time to provide the best possible recommendations to its users, helping to improve the user experience and keep users engaged.

Preventing fraud and abuse with heuristic-aware Machine Learning at Netflix

Netflix is a popular streaming service constantly faced with the challenge of preventing fraudulent activities on its platform. Fraudulent activities can include account sharing, password trading, and other forms of abuse that can result in loss of revenue and harm the user experience. To address these challenges, Netflix has developed a heuristic-aware Machine Learning system designed to prevent fraudulent activities on its platform. The system uses a combination of Machine Learning algorithms, heuristics, and human insights to identify and prevent fraudulent activities.

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One of the system's key features is its ability to detect anomalies in user behavior. The system monitors user activity on the platform and looks for patterns that are outside of the norm. For example, it can detect when a user is accessing the platform from an unusual location or is streaming an unusually large amount of content in a short period of time. These anomalies are then flagged for review by the system or human moderators. Another essential feature of the system is its ability to adapt to changing patterns of fraud and abuse. It uses Machine Learning algorithms to analyze fraudulent activity patterns and identify new types of fraud as they emerge. This allows the system to improve its ability to detect and prevent fraudulent activities continually.

For example, the system can flag accounts accessed from multiple devices simultaneously or used to stream content from multiple locations in a short period. These heuristics are designed to identify potential fraud and abuse in real-time, allowing the system to take action before the activity causes harm.

Check out our new guide to learn how YouTube uses ML To Personalize Your Experience!


Netflix has been a pioneer in the application of Machine Learning to customize content suggestions, improve search algorithms, and detect fraud and abuse. Their large and diversified dataset, together with their engineering experience, allowed them to create cutting-edge Machine Learning algorithms that have set new standards for dependability and scalability. Yet, gaining reliability in Machine Learning is a continual process that necessitates regular monitoring, iteration, and improvement. In this sense, Netflix has made significant investments in cultivating a culture of experimentation and testing, in which engineers and data scientists collaborate closely to discover and address possible issues before they harm users. As a result, Netflix has been able to provide millions of consumers with a smooth, personalized viewing experience.

Interview Questions

1. Can you explain the role of the validation framework built on top of Flink in ensuring high-quality, error-free data is fed into the ML models?

The validation framework in Flink ensures that high-quality, error-free data is fed into the ML models. It ingests raw data from various sources and applies rules to validate the data based on quality requirements for the specific ML model. Checks include ensuring data is numeric and consistent across sources and flagging errors for any data that fails validation rules. By using the validation framework, Netflix can improve the accuracy of its models and user recommendations.

2. What is the relevance of bias-variance decomposition in practical applications such as Netflix's recommendation system?

Bias-variance decomposition is a technique used to understand why ranking algorithms can make mistakes and how to fix them. When the algorithm consistently makes the same mistake, like recommending romantic comedies to someone who only likes action movies, that's called a bias. When the algorithm makes different mistakes each time, like recommending an action movie that someone doesn't like after they enjoyed others, that's called variance. By understanding these different types of mistakes, we can improve the algorithm's accuracy by balancing the trade-off between bias and variance. This can be done by changing the algorithm's design or by using techniques like ensemble methods or feature selection to reduce the mistakes caused by bias and variance.

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