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Displaying captions

This guide explains how to display captions in Remotion, assuming you already have captions in the Caption format - see Transcribing audio for how to generate them.

Fetching captions​

First, fetch your captions JSON file. Use useDelayRender() to hold the render until the captions are loaded:

Fetching captions
import {useState, useEffect, useCallback} from 'react';
import {AbsoluteFill, staticFile, useDelayRender} from 'remotion';
import type {Caption} from '@remotion/captions';

export const MyComponent: React.FC = () => {
  const [captions, setCaptions] = useState<Caption[] | null>(null);
  const {delayRender, continueRender, cancelRender} = useDelayRender();
  const [handle] = useState(() => delayRender());

  const fetchCaptions = useCallback(async () => {
    try {
      const response = await fetch(staticFile('captions.json'));
      const data = await response.json();
      setCaptions(data);
      continueRender(handle);
    } catch (e) {
      cancelRender(e);
    }
  }, [continueRender, cancelRender, handle]);

  useEffect(() => {
    fetchCaptions();
  }, [fetchCaptions]);

  if (!captions) {
    return null;
  }

  return <AbsoluteFill>{/* Render captions here */}</AbsoluteFill>;
};

Creating pages​

Use createTikTokStyleCaptions() to group captions into pages. The combineTokensWithinMilliseconds option controls how many words appear at once:

Creating caption pages

const {pages} = useMemo(() => {
  return createTikTokStyleCaptions({
    captions,
    combineTokensWithinMilliseconds: SWITCH_CAPTIONS_EVERY_MS,
  });
}, [captions]);

Rendering with Sequences​

Map over the pages and render each one in a <Sequence>. Calculate the start frame and duration from the page timing:

Rendering caption pages

const CaptionedContent: React.FC = () => {
  const {fps} = useVideoConfig();

  return (
    <AbsoluteFill>
      {pages.map((page, index) => {
        const nextPage = pages[index + 1] ?? null;
        const startFrame = (page.startMs / 1000) * fps;
        const endFrame = Math.min(nextPage ? (nextPage.startMs / 1000) * fps : Infinity, startFrame + (SWITCH_CAPTIONS_EVERY_MS / 1000) * fps);
        const durationInFrames = endFrame - startFrame;

        if (durationInFrames <= 0) {
          return null;
        }

        return (
          <Sequence key={index} from={startFrame} durationInFrames={durationInFrames}>
            <CaptionPage page={page} />
          </Sequence>
        );
      })}
    </AbsoluteFill>
  );
};

Rendering a caption page​

A caption page contains tokens which you can use to highlight the currently spoken word. Here's an example that highlights words as they are spoken:

Rendering a caption page with word highlighting
import {AbsoluteFill, useCurrentFrame, useVideoConfig} from 'remotion';
import type {TikTokPage} from '@remotion/captions';

const HIGHLIGHT_COLOR = '#39E508';

const CaptionPage: React.FC<{page: TikTokPage}> = ({page}) => {
  const frame = useCurrentFrame();
  const {fps} = useVideoConfig();

  // Current time relative to the start of the sequence
  const currentTimeMs = (frame / fps) * 1000;
  // Convert to absolute time by adding the page start
  const absoluteTimeMs = page.startMs + currentTimeMs;

  return (
    <AbsoluteFill
      style={{
        justifyContent: 'center',
        alignItems: 'center',
      }}
    >
      <div
        style={{
          fontSize: 80,
          fontWeight: 'bold',
          textAlign: 'center',
          // Preserve whitespace in captions
          whiteSpace: 'pre',
        }}
      >
        {page.tokens.map((token) => {
          const isActive = token.fromMs <= absoluteTimeMs && token.toMs > absoluteTimeMs;

          return (
            <span
              key={token.fromMs}
              style={{
                color: isActive ? HIGHLIGHT_COLOR : 'white',
              }}
            >
              {token.text}
            </span>
          );
        })}
      </div>
    </AbsoluteFill>
  );
};

Full example​

Show full example
Full captioned video example
import {useState, useEffect, useCallback, useMemo} from 'react';
import {AbsoluteFill, Sequence, staticFile, useCurrentFrame, useDelayRender, useVideoConfig} from 'remotion';
import {createTikTokStyleCaptions} from '@remotion/captions';
import type {Caption, TikTokPage} from '@remotion/captions';

const SWITCH_CAPTIONS_EVERY_MS = 1200;
const HIGHLIGHT_COLOR = '#39E508';

const CaptionPage: React.FC<{page: TikTokPage}> = ({page}) => {
  const frame = useCurrentFrame();
  const {fps} = useVideoConfig();
  const currentTimeMs = (frame / fps) * 1000;
  const absoluteTimeMs = page.startMs + currentTimeMs;

  return (
    <AbsoluteFill
      style={{
        justifyContent: 'center',
        alignItems: 'center',
      }}
    >
      <div
        style={{
          fontSize: 80,
          fontWeight: 'bold',
          textAlign: 'center',
          whiteSpace: 'pre',
        }}
      >
        {page.tokens.map((token) => {
          const isActive = token.fromMs <= absoluteTimeMs && token.toMs > absoluteTimeMs;

          return (
            <span
              key={token.fromMs}
              style={{
                color: isActive ? HIGHLIGHT_COLOR : 'white',
              }}
            >
              {token.text}
            </span>
          );
        })}
      </div>
    </AbsoluteFill>
  );
};

export const CaptionedVideo: React.FC = () => {
  const [captions, setCaptions] = useState<Caption[] | null>(null);
  const {delayRender, continueRender, cancelRender} = useDelayRender();
  const [handle] = useState(() => delayRender());
  const {fps} = useVideoConfig();

  const fetchCaptions = useCallback(async () => {
    try {
      const response = await fetch(staticFile('captions.json'));
      const data = await response.json();
      setCaptions(data);
      continueRender(handle);
    } catch (e) {
      cancelRender(e);
    }
  }, [continueRender, cancelRender, handle]);

  useEffect(() => {
    fetchCaptions();
  }, [fetchCaptions]);

  const {pages} = useMemo(() => {
    return createTikTokStyleCaptions({
      captions: captions ?? [],
      combineTokensWithinMilliseconds: SWITCH_CAPTIONS_EVERY_MS,
    });
  }, [captions]);

  return (
    <AbsoluteFill style={{backgroundColor: 'black'}}>
      {pages.map((page, index) => {
        const nextPage = pages[index + 1] ?? null;
        const startFrame = (page.startMs / 1000) * fps;
        const endFrame = Math.min(nextPage ? (nextPage.startMs / 1000) * fps : Infinity, startFrame + (SWITCH_CAPTIONS_EVERY_MS / 1000) * fps);
        const durationInFrames = endFrame - startFrame;

        if (durationInFrames <= 0) {
          return null;
        }

        return (
          <Sequence key={index} from={startFrame} durationInFrames={durationInFrames}>
            <CaptionPage page={page} />
          </Sequence>
        );
      })}
    </AbsoluteFill>
  );
};

Next steps​

You can customize the appearance of your captions:

  • Use fitText() from @remotion/layout-utils to automatically scale text to fit the video width
  • Add animations for enter/exit effects
  • Apply CSS text stroke for better visibility:
<div
  style={{
    WebkitTextStroke: '4px black',
    paintOrder: 'stroke',
  }}
>
  {text}
</div>

See also​