einundzwanzig-verein/videos/.opencode/skills/remotion-best-practices/rules/extract-frames.md

name, description, metadata

name	description	metadata
extract-frames	Extract frames from videos at specific timestamps using Mediabunny	tags frames, extract, video, thumbnail, filmstrip, canvas

Extracting frames from videos

Use Mediabunny to extract frames from videos at specific timestamps. This is useful for generating thumbnails, filmstrips, or processing individual frames.

The extractFrames() function

This function can be copy-pasted into any project.

import {
  ALL_FORMATS,
  Input,
  UrlSource,
  VideoSample,
  VideoSampleSink,
} from "mediabunny";

type Options = {
  track: { width: number; height: number };
  container: string;
  durationInSeconds: number | null;
};

export type ExtractFramesTimestampsInSecondsFn = (
  options: Options
) => Promise<number[]> | number[];

export type ExtractFramesProps = {
  src: string;
  timestampsInSeconds: number[] | ExtractFramesTimestampsInSecondsFn;
  onVideoSample: (sample: VideoSample) => void;
  signal?: AbortSignal;
};

export async function extractFrames({
  src,
  timestampsInSeconds,
  onVideoSample,
  signal,
}: ExtractFramesProps): Promise<void> {
  using input = new Input({
    formats: ALL_FORMATS,
    source: new UrlSource(src),
  });

  const [durationInSeconds, format, videoTrack] = await Promise.all([
    input.computeDuration(),
    input.getFormat(),
    input.getPrimaryVideoTrack(),
  ]);

  if (!videoTrack) {
    throw new Error("No video track found in the input");
  }

  if (signal?.aborted) {
    throw new Error("Aborted");
  }

  const timestamps =
    typeof timestampsInSeconds === "function"
      ? await timestampsInSeconds({
          track: {
            width: videoTrack.displayWidth,
            height: videoTrack.displayHeight,
          },
          container: format.name,
          durationInSeconds,
        })
      : timestampsInSeconds;

  if (timestamps.length === 0) {
    return;
  }

  if (signal?.aborted) {
    throw new Error("Aborted");
  }

  const sink = new VideoSampleSink(videoTrack);

  for await (using videoSample of sink.samplesAtTimestamps(timestamps)) {
    if (signal?.aborted) {
      break;
    }

    if (!videoSample) {
      continue;
    }

    onVideoSample(videoSample);
  }
}

Basic usage

Extract frames at specific timestamps:

await extractFrames({
  src: "https://remotion.media/video.mp4",
  timestampsInSeconds: [0, 1, 2, 3, 4],
  onVideoSample: (sample) => {
    const canvas = document.createElement("canvas");
    canvas.width = sample.displayWidth;
    canvas.height = sample.displayHeight;
    const ctx = canvas.getContext("2d");
    sample.draw(ctx!, 0, 0);
  },
});

Creating a filmstrip

Use a callback function to dynamically calculate timestamps based on video metadata:

const canvasWidth = 500;
const canvasHeight = 80;
const fromSeconds = 0;
const toSeconds = 10;

await extractFrames({
  src: "https://remotion.media/video.mp4",
  timestampsInSeconds: async ({ track, durationInSeconds }) => {
    const aspectRatio = track.width / track.height;
    const amountOfFramesFit = Math.ceil(
      canvasWidth / (canvasHeight * aspectRatio)
    );
    const segmentDuration = toSeconds - fromSeconds;
    const timestamps: number[] = [];

    for (let i = 0; i < amountOfFramesFit; i++) {
      timestamps.push(
        fromSeconds + (segmentDuration / amountOfFramesFit) * (i + 0.5)
      );
    }

    return timestamps;
  },
  onVideoSample: (sample) => {
    console.log(`Frame at ${sample.timestamp}s`);

    const canvas = document.createElement("canvas");
    canvas.width = sample.displayWidth;
    canvas.height = sample.displayHeight;
    const ctx = canvas.getContext("2d");
    sample.draw(ctx!, 0, 0);
  },
});

Cancellation with AbortSignal

Cancel frame extraction after a timeout:

const controller = new AbortController();

setTimeout(() => controller.abort(), 5000);

try {
  await extractFrames({
    src: "https://remotion.media/video.mp4",
    timestampsInSeconds: [0, 1, 2, 3, 4],
    onVideoSample: (sample) => {
      using frame = sample;
      const canvas = document.createElement("canvas");
      canvas.width = frame.displayWidth;
      canvas.height = frame.displayHeight;
      const ctx = canvas.getContext("2d");
      frame.draw(ctx!, 0, 0);
    },
    signal: controller.signal,
  });

  console.log("Frame extraction complete!");
} catch (error) {
  console.error("Frame extraction was aborted or failed:", error);
}

Timeout with Promise.race

const controller = new AbortController();

const timeoutPromise = new Promise<never>((_, reject) => {
  const timeoutId = setTimeout(() => {
    controller.abort();
    reject(new Error("Frame extraction timed out after 10 seconds"));
  }, 10000);

  controller.signal.addEventListener("abort", () => clearTimeout(timeoutId), {
    once: true,
  });
});

try {
  await Promise.race([
    extractFrames({
      src: "https://remotion.media/video.mp4",
      timestampsInSeconds: [0, 1, 2, 3, 4],
      onVideoSample: (sample) => {
        using frame = sample;
        const canvas = document.createElement("canvas");
        canvas.width = frame.displayWidth;
        canvas.height = frame.displayHeight;
        const ctx = canvas.getContext("2d");
        frame.draw(ctx!, 0, 0);
      },
      signal: controller.signal,
    }),
    timeoutPromise,
  ]);

  console.log("Frame extraction complete!");
} catch (error) {
  console.error("Frame extraction was aborted or failed:", error);
}