This is a script that downloads a file using multi-segmentation. Making multiple connections to the url and downloading the file in segments and then merges all the downloaded data after download is completed

multisegment-downloader.ts

import axios from "axios";
import * as fs from "node:fs";
import * as path from "node:path";

interface DownloadSegment {
  start: number;
  end: number;
  index: number;
}

async function getFileSize(url: string): Promise<number> {
  const response = await axios.head(url);
  return parseInt(response.headers["content-length"]);
}

async function downloadSegment(
  url: string,
  segment: DownloadSegment,
  outputDir: string
): Promise<string> {
  const { start, end, index } = segment;
  console.log(`Segment Download started start: ${start} end: ${end}`);

  const outputPath = path.join(outputDir, `part_${index}`);
  const writer = fs.createWriteStream(outputPath);

  return new Promise((resolve, reject) => {
    axios({
      method: "get",
      url: url,
      headers: { Range: `bytes=${start}-${end}` },
      responseType: "stream",
    })
      .then((response) => {
        response.data.pipe(writer);
        let error: any = null;
        writer.on("error", (err) => {
          error = err;
          writer.close();
          reject(err);
        });
        writer.on("close", () => {
          if (!error) {
            console.log(`Downloaded segment ${index} (bytes ${start}-${end})`);
            resolve(outputPath);
          }
        });
      })
      .catch((err) => {
        reject(err);
      });
  });
}

async function downloadFile(
  url: string,
  segments: number,
  outputFilePath: string
) {
  const fileSize = await getFileSize(url);
  const segmentSize = Math.ceil(fileSize / segments);
  const outputDir = path.dirname(outputFilePath);
  const segmentPaths: string[] = [];

  const segmentPromises = Array.from({ length: segments }, (_, index) => {
    const start = index * segmentSize;
    const end = index === segments - 1 ? fileSize - 1 : start + segmentSize - 1;
    const segment: DownloadSegment = { start, end, index };
    return downloadSegment(url, segment, outputDir).then((path) =>
      segmentPaths.push(path)
    );
  });

  await Promise.all(segmentPromises);

  // Merge all parts
  const writeStream = fs.createWriteStream(outputFilePath);
  for (const segmentPath of segmentPaths.sort()) {
    const data = fs.readFileSync(segmentPath);
    writeStream.write(data);
    fs.unlinkSync(segmentPath); // Delete segment after merging
  }
  writeStream.close();
  console.log(`Download complete: ${outputFilePath}`);
}

// Example usage

const url =
  "https://rr4---sn-qxaeenl6.googlevideo.com/videoplayback?expire=1731000837&ei=pKUsZ_OXNpKJ9fwP3NO2kAc&ip=34.96.33.87&id=o-AKkWUuNwaTJIgO01fTpJnQs7F2_458w2KqLEX4xhDQjF&itag=137&source=youtube&requiressl=yes&xpc=EgVo2aDSNQ%3D%3D&met=1730979237%2C&mh=DQ&mm=31%2C29&mn=sn-qxaeenl6%2Csn-qxaelned&ms=au%2Crdu&mv=u&mvi=4&pl=27&rms=au%2Cau&vprv=1&svpuc=1&mime=video%2Fmp4&rqh=1&gir=yes&clen=101803581&dur=635.720&lmt=1726430152436097&mt=1730979090&fvip=2&keepalive=yes&fexp=51312688%2C51326932&c=IOS&txp=5535434&sparams=expire%2Cei%2Cip%2Cid%2Citag%2Csource%2Crequiressl%2Cxpc%2Cvprv%2Csvpuc%2Cmime%2Crqh%2Cgir%2Cclen%2Cdur%2Clmt&sig=AJfQdSswRAIgWLZzJ20EWzch7xywvZuuRRk5sxubZli9CNkRIRMx6QICIENKy_k_PjSWKYVF0tV7eSyzbEIlebNcA4qGkMqepbKN&lsparams=met%2Cmh%2Cmm%2Cmn%2Cms%2Cmv%2Cmvi%2Cpl%2Crms&lsig=ACJ0pHgwRAIgC3OHLLVbbxFtUgic47v2ENYwkJYbSt0lrNWpIveaHOQCIF4wLMfSZmaCmYPrytRux6dBgRpCo_Cqdq3riZNNl-am";
const outputFilePath = path.resolve("./largefile.mp4");

downloadFile(url, 10, outputFilePath)
  .then(() => console.log("File downloaded successfully"))
  .catch((error) => console.error("Download failed", error));