How to automatically add subtitles to videos with API

Your videos are getting ignored: Here’s why

Did you know 85% of social media videos are watched on mute? That means most viewers never hear your audio but they still expect to understand your content.

Now think about a busy commuter scrolling through their phone, or someone in a noisy café. They stop on your video… but without subtitles, it’s meaningless. A quick swipe, and your content is forgotten.

This isn’t just about engagement, it’s about survival. Subtitles are the difference between a video that’s watched and one that’s ignored. They make your content accessible, searchable, and impossible to miss even with the sound off.

‍But here’s the problem: Adding subtitles isn’t easy especially when you’re dealing with hundreds (or thousands) of videos. Manual transcription is time-consuming, expensive, and painfully slow.

So how do you automate subtitles without the headache? Let’s dive in.

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What are subtitles? 

A subtitle is a text version of spoken dialogue in a video, allowing viewers to follow along with the conversation in the same language as the audio. Subtitles help overcome language barriers, clarify speech, and ensure that viewers can engage with the content even in sound-sensitive environments.
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Many people confuse subtitles with captions, but they serve different purposes:

• Subtitles focus solely on translating or transcribing spoken dialogue. They help viewers understand conversations, especially if the audio is unclear or in a foreign language.
• Captions go a step further by including non-verbal sounds such as music, background noises, and sound effects. They are designed for audiences who are deaf or hard of hearing, ensuring they get the full audio experience even without sound.

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For example, if you’re watching a movie in a different language, subtitles help you understand the dialogue. But if you’re in a silent mode or have hearing difficulties, captions provide full context by describing sounds like [dramatic music playing] or [door creaks open].

In short, subtitles ensure your video remains accessible, whether your audience is watching on mute, struggling with an accent, or simply needs a little extra clarity.

To learn more about captions and subtitles, check out our blog Captions vs Subtitles.‍

Challenges in adding subtitles to videos

Adding subtitles isn’t just about transcribing speech it’s about ensuring accuracy, synchronization, and readability. For developers, automating this process comes with several challenges that can affect the viewing experience. Here’s what makes subtitle generation tricky:

1. Accuracy of speech recognition: Automatic subtitle tools rely on speech recognition, but they often struggle with accents, background noise, and complex terminology. Misinterpretations can lead to incorrect or misleading subtitles, reducing clarity instead of improving it.
2. Syncing subtitles with video: Subtitles must appear at the exact moment words are spoken too early, and they spoil the dialogue; too late, and they become distracting. Fast-paced conversations, overlapping speech, or rapid scene transitions make this even harder to get right.
3. Language and localization: Different languages, dialects, and regional accents can pose a challenge for subtitle generation. Literal translations don’t always work cultural nuances, idioms, and local expressions must be accounted for to ensure subtitles make sense rather than just matching words.
4. Text formatting and readability: Subtitles should be clear, unobtrusive, and easy to read, but that requires careful formatting. Developers need to balance font size, color contrast, positioning, and background styling to keep subtitles visible without blocking important visuals.
5. Handling multiple speakers: When multiple people speak in a video, subtitles should clearly indicate who’s talking. Without proper speaker identification, conversations can become confusing especially in interviews, debates, or group discussions.
6. Performance and scalability: Processing subtitles for long or high-resolution videos demands significant computing power. Generating accurate, real-time subtitles without slowing down video playback or overloading system resources is a major technical challenge.

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Why use APIs for subtitle generation?

Traditional subtitle methods, like manual transcription or basic software, are slow, tedious, and prone to errors. APIs change the game, offering a faster, smarter, and more reliable way to create subtitles.

Here’s what makes APIs better:

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Faster processing and real-time subtitle generation

Manually creating subtitles can take hours or even days, depending on the length of the video and the complexity of the dialogue. This delay is especially problematic for live broadcasts, news media, and content creators working with tight deadlines.

Subtitle APIs significantly reduce this turnaround time by processing audio in real time. Instead of transcribing, formatting, and syncing subtitles manually, APIs can automatically generate and insert accurate subtitles into videos within minutes or even seconds. This automation makes them ideal for businesses that need to scale their content production without delays.

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Cost savings by reducing manual effort

Hiring professional transcribers or using dedicated subtitle software can be expensive, especially for companies that produce a high volume of video content. Subtitle APIs eliminate the need for manual transcription and post-production editing, reducing costs by up to 80%.

With an API, businesses can integrate subtitle generation directly into their workflows, reducing the need for human intervention while ensuring consistency and accuracy. This makes subtitle APIs a cost-effective solution for streaming services, media companies, and educational platforms that require subtitles at scale.

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Support for multiple languages and translations

Many businesses today operate in a global market, making multilingual subtitles essential for reaching wider audiences. Subtitle APIs support over 100 languages, allowing developers to generate translated subtitles instantly.

Beyond simple translation, these APIs also preserve tone and meaning, ensuring that subtitles are not just literal translations but accurately reflect local expressions and cultural nuances. This feature is particularly useful for international companies, media platforms, and educators who need to deliver content in multiple languages without losing context.

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Improved Accessibility Features

Subtitle APIs do more than just transcribe speech. They also include accessibility-focused features, such as:

• Speaker identification – Differentiating between multiple speakers in a conversation.·      
• Timestamp synchronization – Ensuring that subtitles appear at the right time to match the audio.·      
• Sound effect descriptions – Capturing important non-verbal sounds, such as background music or environmental noises, which are crucial for viewers with hearing impairments.·      
• Customizable formatting – Allowing developers to adjust the font, size, color, and placement of subtitles to match branding or improve readability.

By providing these advanced features, subtitle APIs help make videos more accessible to a broader audience, including those who are deaf or hard of hearing.

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Easy integration with existing workflows

A key advantage of subtitle APIs is that they seamlessly integrate with existing video production and streaming platforms. Developers can connect these APIs to their content management systems (CMS), video editing software, and live streaming platforms without needing complex configurations.

For example, a media company producing hundreds of videos per month can integrate a subtitle API directly into its workflow, automatically generating and embedding subtitles as soon as a new video is uploaded. This reduces manual effort and ensures that every video is instantly ready for distribution with accurate subtitles.

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How FastPix API can help with subtitle?

This guide will take you through each step of the process, from preparing your video to retrieving transcripts and customizing subtitles.

Step 1: Prepare your video for subtitle generation

Before generating subtitles, ensure that your video’s audio is optimized for accuracy.

Ensure clear audio

• Reduce background noise and remove unnecessary sounds.
• Avoid overlapping dialogue or excessive non-speech audio like music or sound effects.
• Adjust volume levels so that spoken content is clear and distinct.

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Step 2: Upload your video to FastPix

FastPix supports video uploads from two sources:

• Direct upload: Upload videos from your local storage.
• Cloud-based upload: Provide a public URL from cloud storage services like AWS S3, Google Cloud Storage, or FastPix-hosted content.

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Step 3: Enable auto-generated subtitles in your request

To generate subtitles, include the subtitles object in your API request when uploading the video.

1{
2  "inputs": [
3    {
4      "type": "video",
5      "url": "https://example.com/sample.mp4",
6      "startTime": 0,
7      "endTime": 60
8    }
9  ],
10  "metadata": {
11    "key1": "value1"
12  },
13  "subtitles": {
14    "languageName": "english",
15    "metadata": {
16      "key1": "value1"
17    },
18    "languageCode": "en"
19  },
20  "accessPolicy": "public",
21  "maxResolution": "1080p"
22}

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Key parameters

• languageName: Specify the spoken language in the video (e.g., "English").•
• metadata: Add optional metadata to store additional information.•
• languageCode: Define the correct language code for accurate transcription (e.g., "en" for English).

Important: Double-check that the languageCode matches the spoken language in your video, as the subtitle model will use this setting for transcription.

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Step 4: Process the video & generate subtitles

Once the request is submitted, FastPix processes the video using OpenAI's Whisper model. The model transcribes spoken words into text and synchronizes the subtitles with the video.

You can check the processing status using FastPix’s API or platform interface.

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Step 5: Retrieve & download subtitles

Once the subtitles are generated, you can retrieve them in different formats for playback, editing, or integration into other workflows.

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Get a plain text transcript (TXT format)

A plain text transcript contains only the speech content without timestamps.

Use the following URL format to retrieve it:

https://stream.fastpix.io/{PLAYBACK_ID}/text/{TRACK_ID}.txt

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Download WebVTT subtitles (VTT format)

WebVTT files include timestamps and are widely supported by video players.

Use the URL format below:

https://stream.fastpix.io/{PLAYBACK_ID}/text/{TRACK_ID}.vtt

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Retrieve secured transcripts (Signed media)

If your video is protected, you must include a JWT token when requesting subtitles:

https://stream.fastpix.io/{PLAYBACK_ID}/text/{TRACK_ID}.txt?token={JWT}

For WebVTT format:

https://stream.fastpix.io/{PLAYBACK_ID}/text/{TRACK_ID}.vtt?token={JWT}

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Editing and replacing auto-generated subtitles

If the AI-generated subtitles require corrections, follow these steps:

Step 1: Download the existing subtitle file

Retrieve the WebVTT file from:

https://stream.fastpix.io/{PLAYBACK_ID}/text/{TRACK_ID}.vtt
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Step 2: Edit the Subtitle File

Use a text editor or specialized subtitle software like Aegisub or Subtitle Edit to make corrections.
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Step 3: Remove the Auto-Generated Track

Use the Delete Track API to remove the incorrect subtitles.
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Step 4: Upload a New Subtitle Track

Upload your manually corrected subtitles using the Add Track API.

Best practices for high-quality auto-generated subtitles

• Optimize Audio Quality: Clear, high-quality audio ensures accurate transcription.
• Speak Clearly and Consistently: Maintain a steady pace and avoid rapid speech.
• Minimize Background Noise: Reduce music and overlapping voices to enhance clarity.
• Use a Single Language Per Video: The auto-subtitle feature is not designed to handle multilingual speech in one video.

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What if you don’t need an API-based solution?

Not every video creator or business requires an API to generate subtitles. If you only work with a small number of videos or don’t need automation at scale, there are alternative approaches that might be more suitable for your needs. Here’s a look at some manual and software-based methods for adding subtitles:

Built-In subtitle tools in video editors

Most popular video editing software, such as Adobe Premiere Pro and Final Cut Pro, includes basic subtitle editing features. These tools are ideal for small-scale projects, allowing users to manually add subtitles and sync them with video timelines. However, they often require significant manual effort and may not handle complex workflows efficiently.

Online subtitle generators

Platforms like Kapwing and Veed.io provide easy-to-use tools for generating subtitles automatically. While convenient for quick tasks, these tools often lack accuracy, especially in noisy environments or with diverse accents, and are not designed for high-volume or professional-grade subtitle creation.

Conclusion

Automatically adding subtitles to videos using APIs is a simple yet powerful way to make your content accessible to a wider audience.  Whether you're looking to streamline video production or expand your reach, FastPix provides the tools you need for efficient subtitle generation. For a seamless video delivery experience, explore the On-Demand solution to learn how FastPix can help you manage and stream videos effortlessly at scale.