Video annotation: challenges and best practices

Natalie Kudan

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What is video annotation?

Video annotation (or video labeling) adds metadata to a video or image to categorize the content, label objects, or organize the data. The annotated video data is used for training computer vision AI models to perform object detection, facial recognition, and motion tracking in AI systems. In other words, machines learn to analyze images and videos to identify objects such as faces, buildings, and cars. For instance, AI systems can use this information to monitor security footage or automatically track road traffic patterns.

Annotation workflows

With the help of sophisticated video annotation tools, experts can manually label video data. However, augmenting the process with AI can provide faster and more accurate results.

An efficient workflow uses AI to annotate videos and then show the labeled videos to human annotators to correct or adjust the results. In this scenario, non-experts can participate in video annotation, so a larger pool of annotators is available — reducing costs and speeding up projects significantly while improving accuracy.

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Applications of video annotation

Video annotation is a powerful tool to create training data for computer vision models with multiple real-world applications. It can be used to create digital replicas of human behavior and actions, such as hand gestures, walking, or playing an instrument.

Games and simulations

The annotated data can be used to build realistic virtual environments for games or simulations.

Medical research

In the medical field, video annotation is used to track changes in tumors over time and analyze microscopic images of cells.

Sports analytics

Sports analytics use this technology to track player performance and identify game strategies.

AI-based video analysis systems can detect specific activities in a video, such as sports, dancing, or other activities.

Security and surveillance systems

AI video analysis can detect anomalies in videos, such as suspicious activities or objects that could pose a security risk.

Autonomous navigation systems

Navigation systems for self-driving vehicles use annotated video footage to learn to recognize objects in their environment and respond accordingly.

Industrial robotics

Computer vision models in industrial robotics improve safety and efficiency. Annotated video is used for training AI models to identify target objects on production lines, spot defects, sort waste, and sense their surroundings to plan movements.


Computer vision solutions can help monitor self-checkouts to prevent theft. AI can also track patterns of customer traffic in stores to help make decisions on product placement.

How to annotate video: techniques

Video annotation involves labeling visual data with text or other labels and is an important part of many computer vision algorithms. Two main techniques are used for annotating videos: single image and continuous frame.

Single image method

Single image annotation involves labeling a single image from a video, such as a face or object in the frame. This technique of video annotation is suitable for tasks that require annotations on individual frames, including facial recognition and other scenarios involving object identification and detection. Allowing the annotator to focus on one frame at a time can be more efficient than annotating the entire video clip all at once.

Continuous frame method

Continuous frame annotation requires labeling multiple frames in sequence so that annotations for each frame are consistent across the duration of the video clip. This rapid annotation technique is more suitable for complex tasks requiring understanding motion or context across multiple frames, such as activity recognition or autonomous navigation. It can also be more accurate than single-image annotation since it allows the annotator to track objects over longer periods.

Why is annotating videos better than annotating individual images?

By using video data, businesses can achieve more accurate results and gain insights that would be impossible to obtain with image annotation alone. For instance, in the surveillance field, analyzing continuous video streams allows automated alerts for suspicious activities that can be quickly identified and acted upon, reducing potential risks and costs.

In some cases, combining both video annotation techniques can be beneficial to achieve better accuracy — for example, by using single image annotation to identify objects in each frame and then using continuous frame annotation to assess their trajectories over time. Similarly, if you have a particularly complex task that requires a detailed assessment of each object's movements over time, then combining both techniques may help improve accuracy rates.

Ultimately, choosing between these two techniques depends on your specific requirements and data type. It's important to consider factors such as complexity and accuracy when making your decision.

Video annotation software

Because video annotation is highly complex, there are many specialized services available that offer sophisticated video annotation tools. Well-designed tools are an important component for efficient and high-quality video annotations.

Toloka includes data labeling tools for a range of methods of annotating video: bounding box annotation, polygon annotation, key points annotation, semantic segmentation, classification, and flexible customization for bespoke projects.

Bounding boxes are an easy way to select an area on an image. This technique is the least accurate, but it is the easiest way to use a large crowd for fast labeling without extensive training or special skills.

Polygons capture more complex shapes by connecting dots around an object with straight lines. This technique is used in segmentation methods.

Key points are generally used for facial recognition by defining points on the eyes, nose, and mouth of people.

How automation improves the video annotation process

Auto-labeling (or auto-annotation) can greatly improve the video annotation process. Auto-labeling is a form of automated analysis which uses machine learning algorithms to tag, label, or categorize objects and scenes in videos. By using auto-labeling, companies can reduce costs associated with manual video annotation and achieve more accurate results.

Faster results

The main advantage of auto-labeling is that it allows for faster completion times than manual labeling. Since the automation process does not require human interaction, it eliminates the need for annotators to review each frame and tag each object manually. This saves time and resources which would otherwise be spent on manual labor.

Better accuracy

On straightforward annotation tasks, auto-labeling provides better consistency because it removes the problem of human error. Additionally, since AI-based auto-labeling systems can learn from their mistakes, they become more proficient at accurately identifying objects over time.

Quality assurance checks allow businesses to verify whether the annotated labels match the actual content of the video footage and make sure that any discrepancies between human annotations and machine labels are identified quickly so they can be corrected accordingly. This helps businesses get accurate results from their video annotation projects quickly and cost-effectively.

Challenges of implementing AI for video annotation projects

The use of Artificial Intelligence (AI) for video annotation has its challenges. Despite the ability of AI-based algorithms to label, classify, or categorize objects and actions in videos, some potential issues must be considered for accurate results.


Although accuracy is a strength of automated annotation, it is also the biggest challenge. An effective model requires proper training with strong datasets to recognize visuals correctly. Creating the necessary datasets can be a problem when resources are limited. Moreover, it can be expensive for businesses to retain qualified experts in AI and video annotation.

Data privacy and security

It is essential that data privacy and security laws such as GDPR or CCPA are adhered to when dealing with personal information collected during these projects.

Continual retraining

Manual input may be needed at times to modify results generated by AI models; this may require regular updates on models due to advances in technology or sensor capabilities which can add further complexity to the equation for businesses already under pressure from resource constraints.

Best practices for video annotation

By following best practices for successful video annotation projects, businesses can obtain more accurate results from AI-driven tasks while reducing costs associated with traditional manual methods of annotation. Here are some tips for successful video annotation:

Organize data into manageable chunks

Managing the data is one of the main challenges of a large-scale video annotation project. By dividing the data into smaller, manageable chunks, it becomes easier to manage and annotate a video. Additionally, this ensures that each chunk receives sufficient attention while maintaining an accurate and consistent level of quality throughout the project.

Combine auto-annotation and human annotation

Design workflows that use automation for straightforward tasks and human input for handling edge cases or evaluating results. Toloka's solutions offer pre-trained models to handle auto-labeling with reliable accuracy, combined with human annotators who can provide more nuanced annotations than automated algorithms alone.

Use quality assurance checks

Quality assurance checks should be incorporated into the process to optimize the accuracy of results. With Toloka, businesses can access a team of human annotators for their video annotation tasks and get quality assurance checks to make sure their results are correct.

Test different methods

To achieve better accuracy, test different video annotation methods to find the one that works best. For example, some projects may require single image annotations, while others may require continuous frame annotations. By testing different methods, businesses can identify which technique will yield more accurate results for their particular task.

Evaluate Results

Finally, businesses should evaluate the results of annotated videos to identify improvement areas and make necessary adjustments as needed. This could include changing techniques or processes used during the project or training models on new datasets to obtain more accurate results.

Human annotators can efficiently evaluate the output of computer vision models to provide metrics. Continuous monitoring with human-in-the-loop workflows is a good approach for catching problems in the model before they become serious problems in the real world.

How Toloka can help overcome the challenges of video annotation

Video annotation can often present several challenges for businesses. From accuracy and resource constraints to the need to recruit qualified personnel to data privacy and security laws, these issues can be daunting.

Toloka offers a solution to these problems. Companies have access to a global pool of talent which helps them quickly and cost-effectively produce high-quality results with an emphasis on data security. Additionally, Toloka's platform combines manual input with automated labeling solutions for ground truth accuracy and superior scalability.

Toloka allows businesses to benefit from faster completion times than manual annotation methods and achieve improved accuracy. Moreover, Toloka provides access to experts in AI and data labeling who can develop custom solutions tailored specifically for video annotation tasks.

Finally, quality assurance checks ensure high-quality video annotation even when dealing with more sophisticated tasks like motion tracking or facial recognition that require an understanding of context across multiple video frames together.

Maximizing the efficiency of video annotation with human input

In summary, Toloka’s data labeling platform is an invaluable asset for businesses looking for effective solutions to the challenges posed by video annotation projects, such as accuracy concerns, resource constraints, and data privacy protocols. By leveraging Toloka's global pool of talent combined with automated techniques and expert advice in AI-driven solutions, companies can maximize the efficiency of their projects.

Toloka combines machine learning models with human intelligence to annotate video footage quickly without sacrificing the accuracy of results. Our data labeling platform supports flexible solutions for a wide range of video annotation capabilities.

To request a live demo or discuss pricing and timeframes for your video annotation project, contact our team of experts.

Article written by:
Natalie Kudan

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