Dan Kokotov: Speech Recognition with AI and Humans | Lex Fridman Podcast #151 | Summary and Q&A

January 4, 2021
Lex Fridman Podcast
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Dan Kokotov: Speech Recognition with AI and Humans | Lex Fridman Podcast #151


Rev.ai is a leading speech-to-text AI engine that offers transcription and captioning services through a user-friendly platform, making it easier for people to access and search the content of audio and video files.

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Key Insights

  • 🐕‍🦺 Rev.ai is built on a two-sided marketplace model, connecting clients who need transcription and captioning services with freelance transcribers.
  • 👤 The company aims to improve the user experience of transcription and captioning services by providing a simple and streamlined platform.
  • ☠️ Rev.ai's ASR technology has an accuracy rate of around 86%, but human review and correction are still essential for higher accuracy.
  • 😯 The company is focused on expanding its services and exploring new applications for its speech-to-text AI technology.
  • 👻 Platforms like Spotify and podcast players could benefit from incorporating transcript features, allowing for searchability and better user experiences.
  • 🥶 The balance between free speech, content moderation, and encouraging positive conversations poses challenges for platforms like Twitter and YouTube.


the following is a conversation with dan kokodav vp of engineering at rev.ai which is by many metrics the best speech-to-text ai engine in the world rev in general is a company that does captioning and transcription of audio by humans and by ai i've been using their services for a couple years now and planning to use rev to add both captions and tr... Read More

Questions & Answers

Q: How does Rev.ai's transcription and captioning service work?

Rev.ai offers a user-friendly platform where users can upload audio or video files and receive transcriptions or captions in return. The process involves using automated speech recognition (ASR) technology as a base, which is then corrected and reviewed by human transcribers to ensure accuracy.

Q: What is the difference between Rev.com and Rev.ai?

While Rev.com focuses on human transcription and captioning services, Rev.ai is the company's AI-powered speech-to-text service. Rev.com caters to a wide range of language-related transcription and translation needs, while Rev.ai specifically focuses on speech-related services.

Q: How accurate is Rev.ai's automated speech recognition (ASR) technology?

Rev.ai claims to have one of the best ASR technologies in the industry and achieves an accuracy rate of around 86%, measured by the Word Error Rate (WER). However, human review and correction are still necessary to improve the accuracy further.

Q: What are the benefits of using Rev.ai's transcription and captioning services?

Rev.ai offers a fast and efficient solution for transcribing and captioning audio and video content. The platform eliminates the need for manual searching and skimming through long recordings, making it easier to find and reference specific information. This benefits content creators, researchers, journalists, and anyone who relies on accurate transcripts or captions.


In this conversation, Dan Kokodav, VP of Engineering at Rev.ai, discusses the origins of Rev and how it has revolutionized transcription and captioning services. Rev was developed to improve upon the model of freelancer marketplaces like Upwork, with a focus on simplifying the process for both customers and freelancers. The goal was to create a platform that made it easy to request transcription and receive accurate and timely results. Using machine learning models for automatic speech recognition (ASR), Rev has achieved impressive accuracy, although there is still a gap between human and machine performance. The company is constantly working towards improving its ASR technology and exploring new applications through Rev.ai.

Q: What is Rev and how does it work?

Rev is a platform that offers transcription and captioning services. It was developed to simplify the process of requesting transcription and provide accurate and timely results. Customers can upload their audio or video files to the platform, and Rev offers both human transcription and ASR services. The platform hides the details of the transcription process from the customers and provides them with standardized results, making it a frictionless experience.

Q: Can Rev expand to other verticals?

Initially, Rev focused on translation and transcription services, as those were the areas considered suitable for standardization. However, the company is now primarily focused on speech-to-text and language services. While there are no immediate plans to expand into other verticals, the goal is to explore new applications and see what people can build with Rev's ASR technology.

Q: What is the demographic of Rev's freelancers?

Rev's freelancers, also called "Revers," come from all walks of life. The majority of them are located in the United States, as most of the work requires proficiency in English. However, there are freelancers from various English-speaking countries. Rev offers opportunities for people who prefer flexible work hours, work-from-home moms, individuals with social anxiety, or those who want to work while living a non-traditional lifestyle.

Q: What is the transcription process like for Revers?

Revers log into their workspace on the Rev platform, where they can see a list of audio files available for transcription. Rev provides tools for Revers to select the files they prefer based on their preferences, such as length, subject, or source country. Once they choose a file, they work in a specialized transcription editor that helps correct the automated speech recognition (ASR) draft. The level of correction depends on the audio quality, with some audios requiring a complete transcription from scratch. The process involves careful listening, dealing with accents, and providing accurate transcriptions.

Q: How accurate is Rev's ASR compared to human performance?

Rev's ASR technology is continuously evolving, but it is already considered one of the best in the field. Their ASR system has achieved a word error rate (WER) of around 14% on their test suite. However, human accuracy in transcription is estimated to be around 2-3% WER, so there is still a significant gap between human and machine performance. Rev aims to improve their ASR technology to narrow this gap further by leveraging data, improving models, and exploring new strategies.

Q: Can Rev's ASR technology beat competitors like Google?

Rev believes that it can compete with and surpass technology from companies like Google, Amazon, and Microsoft in the ASR domain. While such companies invest significant resources in ASR research and development, Rev leverages their unique data advantage. Through their freelancers' work, Rev collects high-quality, accurately labeled data that helps train and improve their ASR models. Rev measures itself against these companies and is confident in the accuracy and performance of their ASR technology.

Q: Can Rev's ASR technology achieve real-time transcription?

Real-time transcription, meaning transcribing speech as it happens, is challenging and not currently achievable with Rev's ASR technology. While ASR can enable faster transcription compared to manual transcribing, it cannot match the speed at which humans can type and transcribe speech accurately. The current speed of Rev's ASR technology is roughly 2-3 times longer than the actual audio duration.

Q: What is the future goal for Rev's ASR technology?

The ultimate goal for Rev is to achieve a word error rate (WER) of around 3%, which would be comparable to human performance. However, the path to this goal involves refining and optimizing the different components of their ASR technology. Rev is constantly exploring new ways to leverage their data, such as incorporating edits made by Revers and developing innovative applications using their accurate ASR engine available through Rev.ai.

Q: Does Rev have plans to expand its services beyond transcription and captioning?

Rev's immediate focus is on perfecting their ASR technology and exploring the possibilities of Rev.ai. While they do not have specific plans to expand into other verticals, they are open to discovering new applications and learning from how people use the ASR technology. Rev aims to follow the model of companies like AWS, which provide building blocks and enable developers to create innovative solutions.

Q: How does the Rev platform compare to other similar services like Mechanical Turk?

While Rev and platforms like Mechanical Turk share similarities in providing freelancing opportunities, Rev differentiates itself by focusing on specific services like transcription and captioning. Rev has streamlined the process to make it easy for customers to request the services they need and receive accurate results promptly. The goal is to remove the complexities and friction associated with freelancer marketplaces. In contrast, platforms like Mechanical Turk can be challenging to navigate due to outdated interfaces and limited support for customer needs.


Rev has revolutionized the transcription and captioning services by providing a platform that simplifies the process for both customers and freelancers. With a focus on data quality and accuracy, Rev's ASR technology aims to compete with major companies like Google and Microsoft. While there is still room for improvement, Rev has achieved impressive accuracy in its transcription services. The company is continuously refining its ASR technology and exploring new applications through Rev.ai. With its vision to provide the best ASR engine in the world, Rev aims to empower developers to build innovative solutions and provide a frictionless experience for transcription and captioning services.

Summary & Key Takeaways

  • Rev.ai is a company that provides transcription and captioning services using a combination of human and AI technology.

  • The platform allows users to easily upload audio or video files and receive accurate transcriptions or captions within a short period.

  • The company aims to improve the user experience of transcription and captioning services by offering a simplified and efficient solution.

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