Variable metadata

You may change the duration of the video based on some asynchronously determined data.
The same goes for the width, height and framerate of the video.

Using the `calculateMetadata()` function

Consider a scenario where a video is dynamically specified as a background and the duration of the composition should be aligned with the duration of the video.

Pass a calculateMetadata callback function to a <Composition>. This function should take the combined props and calculate the metadata.

src/Root.tsx
tsx
import { getVideoMetadata } from "@remotion/media-utils";
import { Composition, Video } from "remotion";
 
type MyCompProps = {
  src: string;
};
 
const MyComp: React.FC<MyCompProps> = ({ src }) => {
  return <Video src={src} />;
};
 
export const Root: React.FC = () => {
  return (
    <Composition
      id="MyComp"
      component={MyComp}
      durationInFrames={300}
      fps={30}
      width={1920}
      height={1080}
      defaultProps={{
        src: "https://commondatastorage.googleapis.com/gtv-videos-bucket/sample/BigBuckBunny.mp4",
      }}
      calculateMetadata={async ({ props }) => {
        const data = await getVideoMetadata(props.src);
 
        return {
          durationInFrames: Math.floor(data.durationInSeconds * 30),
        };
      }}
    />
  );
};

src/Root.tsx
tsx
import { getVideoMetadata } from "@remotion/media-utils";
import { Composition, Video } from "remotion";
 
type MyCompProps = {
  src: string;
};
 
const MyComp: React.FC<MyCompProps> = ({ src }) => {
  return <Video src={src} />;
};
 
export const Root: React.FC = () => {
  return (
    <Composition
      id="MyComp"
      component={MyComp}
      durationInFrames={300}
      fps={30}
      width={1920}
      height={1080}
      defaultProps={{
        src: "https://commondatastorage.googleapis.com/gtv-videos-bucket/sample/BigBuckBunny.mp4",
      }}
      calculateMetadata={async ({ props }) => {
        const data = await getVideoMetadata(props.src);
 
        return {
          durationInFrames: Math.floor(data.durationInSeconds * 30),
        };
      }}
    />
  );
};

The props defaults to the defaultProps specified, but may be overriden by passing input props to the render.

Return an object with durationInFrames to change the duration of the video. In addition or instead, you may also return fps, width and height to update the video's resolution and framerate.

It is also possible to transform the props passed to the component by returning a props field at the same time.

With `useEffect()` and `getInputProps()`

In the following example, Remotion is instructed to wait for the getVideoMetadata() promise to resolve before evaluating the composition.

By calling delayRender(), Remotion will be blocked from proceeding until continueRender() is called.

src/Root.tsx
tsx
import { getVideoMetadata } from "@remotion/media-utils";
 
export const Index: React.FC = () => {
  const [handle] = useState(() => delayRender());
  const [duration, setDuration] = useState(1);
 
  useEffect(() => {
    getVideoMetadata(
      "https://commondatastorage.googleapis.com/gtv-videos-bucket/sample/BigBuckBunny.mp4"
    )
      .then(({ durationInSeconds }) => {
        setDuration(Math.round(durationInSeconds * 30));
        continueRender(handle);
      })
      .catch((err) => {
        console.log(`Error fetching metadata: ${err}`);
      });
  }, [handle]);
 
  return (
    <Composition
      id="dynamic-duration"
      component={VideoTesting}
      width={1080}
      height={1080}
      fps={30}
      durationInFrames={duration}
    />
  );
};

src/Root.tsx
tsx
import { getVideoMetadata } from "@remotion/media-utils";
 
export const Index: React.FC = () => {
  const [handle] = useState(() => delayRender());
  const [duration, setDuration] = useState(1);
 
  useEffect(() => {
    getVideoMetadata(
      "https://commondatastorage.googleapis.com/gtv-videos-bucket/sample/BigBuckBunny.mp4"
    )
      .then(({ durationInSeconds }) => {
        setDuration(Math.round(durationInSeconds * 30));
        continueRender(handle);
      })
      .catch((err) => {
        console.log(`Error fetching metadata: ${err}`);
      });
  }, [handle]);
 
  return (
    <Composition
      id="dynamic-duration"
      component={VideoTesting}
      width={1080}
      height={1080}
      fps={30}
      durationInFrames={duration}
    />
  );
};

To dynamically pass a video asset, you may pass input props when rendering and retrieve them inside your React code using getInputProps().

src/Root.tsx
tsx
import { getInputProps } from "remotion";
 
const inputProps = getInputProps();
const src = inputProps.src;

src/Root.tsx
tsx
import { getInputProps } from "remotion";
 
const inputProps = getInputProps();
const src = inputProps.src;

Drawbacks

This technique is not recommended anymore since v4.0, because the useEffect() does not only get executed when Remotion is initially calculating the metadata of the video, but also when spawning a render worker.

Since a render process might be highly concurrent, this might lead to unnecessary API calls and rate limitations.

Using together with dimension overrides

Override parameters such as --width will be given priority and override the variable dimensions you set using calculateMetadata().

The --scale parameter has the highest priority and will be applied after override parameters and calculateMetadata().

Changing dimensions and FPS after the video was designed

If you designed your video with certain dimensions and then want to render a different resolution (e.g. 4K instead of Full HD), you can use output scaling.

If you designed your video with certain FPS and then want to change the frame rate, you can use the <FpsConverter> snippet.

With the `<Player>`

The <Player> will react if the metadata being passed to it changes. There are two viable ways to do dynamically set the metadata of the Player:

1 Perform data fetching using useEffect():

MyApp.tsx
tsx
import { Player } from "@remotion/player";
 
export const Index: React.FC = () => {
  const [duration, setDuration] = useState(1);
 
  useEffect(() => {
    getVideoMetadata(
      "https://commondatastorage.googleapis.com/gtv-videos-bucket/sample/BigBuckBunny.mp4"
    )
      .then(({ durationInSeconds }) => {
        setDuration(Math.round(durationInSeconds * 30));
      })
      .catch((err) => {
        console.log(`Error fetching metadata: ${err}`);
      });
  }, []);
 
  return (
    <Player
      component={VideoTesting}
      compositionWidth={1080}
      compositionHeight={1080}
      fps={30}
      durationInFrames={duration}
    />
  );
};

MyApp.tsx
tsx
import { Player } from "@remotion/player";
 
export const Index: React.FC = () => {
  const [duration, setDuration] = useState(1);
 
  useEffect(() => {
    getVideoMetadata(
      "https://commondatastorage.googleapis.com/gtv-videos-bucket/sample/BigBuckBunny.mp4"
    )
      .then(({ durationInSeconds }) => {
        setDuration(Math.round(durationInSeconds * 30));
      })
      .catch((err) => {
        console.log(`Error fetching metadata: ${err}`);
      });
  }, []);
 
  return (
    <Player
      component={VideoTesting}
      compositionWidth={1080}
      compositionHeight={1080}
      fps={30}
      durationInFrames={duration}
    />
  );
};

2 Call your own calculateMetadata() function reused from your Remotion project:

MyApp.tsx
tsx
import { Player } from "@remotion/player";
 
type Props = {};
 
const calculateMetadataFunction: CalculateMetadataFunction<Props> = () => {
  return {
    props: {},
    durationInFrames: 1,
    width: 100,
    height: 100,
    fps: 30,
  };
};
 
type Metadata = {
  durationInFrames: number;
  compositionWidth: number;
  compositionHeight: number;
  fps: number;
  props: Props;
};
 
export const Index: React.FC = () => {
  const [metadata, setMetadata] = useState<Metadata | null>(null);
 
  useEffect(() => {
    Promise.resolve(
      calculateMetadataFunction({
        defaultProps: {},
        props: {},
        abortSignal: new AbortController().signal,
      })
    )
      .then(({ durationInFrames, props, width, height, fps }) => {
        setMetadata({
          durationInFrames: durationInFrames as number,
          compositionWidth: width as number,
          compositionHeight: height as number,
          fps: fps as number,
          props: props as Props,
        });
      })
      .catch((err) => {
        console.log(`Error fetching metadata: ${err}`);
      });
  }, []);
 
  if (!metadata) {
    return null;
  }
 
  return <Player component={VideoTesting} {...metadata} />;
};

MyApp.tsx
tsx
import { Player } from "@remotion/player";
 
type Props = {};
 
const calculateMetadataFunction: CalculateMetadataFunction<Props> = () => {
  return {
    props: {},
    durationInFrames: 1,
    width: 100,
    height: 100,
    fps: 30,
  };
};
 
type Metadata = {
  durationInFrames: number;
  compositionWidth: number;
  compositionHeight: number;
  fps: number;
  props: Props;
};
 
export const Index: React.FC = () => {
  const [metadata, setMetadata] = useState<Metadata | null>(null);
 
  useEffect(() => {
    Promise.resolve(
      calculateMetadataFunction({
        defaultProps: {},
        props: {},
        abortSignal: new AbortController().signal,
      })
    )
      .then(({ durationInFrames, props, width, height, fps }) => {
        setMetadata({
          durationInFrames: durationInFrames as number,
          compositionWidth: width as number,
          compositionHeight: height as number,
          fps: fps as number,
          props: props as Props,
        });
      })
      .catch((err) => {
        console.log(`Error fetching metadata: ${err}`);
      });
  }, []);
 
  if (!metadata) {
    return null;
  }
 
  return <Player component={VideoTesting} {...metadata} />;
};

Using the calculateMetadata() function​

With useEffect() and getInputProps()​

Drawbacks​

Using together with dimension overrides​

Changing dimensions and FPS after the video was designed​

With the <Player>​

See also​