使用 Node JS、FFMPEG 和 Bento4 进行流式传输的视频编码器

本文我们将使用 Bento4 和 ffmpeg 制作一个强大的视频编码解决方案。相比《使用 Node JS 和 FFMPEG 编写视频编码器》，唯一的变化是，上次我们使用 ffmpeg 完成了包括视频分割在内的所有编码操作，而这次将使用 Bento4 完成这部分操作。因此，将视频转换为不同码率的输出将由 ffmpeg 完成，而将编码视频集分割并转换为 dash 格式将由 bento4 完成。

现在您可能想知道什么是转换为片段视频。普通的 mp4 文件和片段式 mp4 文件并不相似。片段式 MP4 包含一系列片段，如果您的服务器支持字节范围请求，可以单独请求这些片段。MP4 文件是由许多称为原子（或 “盒子”）的离散单元组成的。因此，普通 mp4 和片段式 mp4 中的原子排列是不同的。

第一步，安装 Bento4。我们将在本地环境中安装 Bento4，对于 Mac 用户，只需执行以下命令：

brew install bento4

对于其他操作系统，请访问 https://www.bento4.com/downloads/ 下载压缩文件，并在路径中添加 bento4 bin 文件夹的路径。

现在，正如我之前提到的有 3 件事要做：

• 将视频编码为不同的分辨率和比特率
• 将编码后的视频进行分段
• 快速转换这些分段文件

让我们先解决第一个问题。创建一个名为 encoder.js 的文件，并添加以下几行。

const ffmpegStatic = require("ffmpeg-static");
const ffmpeg = require("fluent-ffmpeg");
const fs = require("fs");

ffmpeg.setFfmpegPath(ffmpegStatic);

const bitrates = [
  {
    resolution: "1280x720",
    videoBitrate: "1500k",
    audioBitrate: "128k",
    outputName: "output_720p.mp4",
  },
  {
    resolution: "854x480",
    videoBitrate: "500k",
    audioBitrate: "96k",
    outputName: "output_480p.mp4",
  },
  {
    resolution: "640x360",
    videoBitrate: "250k",
    audioBitrate: "64k",
    outputName: "output_360p.mp4",
  },
];

const encodeVideo = (inputVideo, outputFolder, config) => {
  return new Promise((resolve, reject) => {
    ffmpeg(inputVideo)
      .videoCodec("libx264")
      .audioCodec("aac")
      .videoBitrate(config.videoBitrate)
      .audioBitrate(config.audioBitrate)
      .size(config.resolution)
      .output(`${outputFolder}/${config.outputName}`)
      .on("end", () => {
        console.log(`Finished encoding ${config.outputName}`);
        resolve(`${outputFolder}/${config.outputName}`);
      })
      .on("error", (err) => {
        console.error(`Error encoding ${config.outputName}: ${err}`);
        reject(err);
      })
      .run();
  });
};

const encoder = async () => {
  const inputVideo = "input.mp4";
  const outputDirectory = "output_folder";

  const permissions = 0o777;

  try {
    if (fs.existsSync(outputDirectory)) {
      fs.rmSync(outputDirectory, { recursive: true });
    }

    fs.mkdirSync(outputDirectory);
    fs.chmodSync(outputDirectory, permissions);

    const encodingQueue = [];

    for (const config of bitrates) {
      encodingQueue.push(encodeVideo(inputVideo, outputDirectory, config));
    }

    const outPutVideoFiles = await Promise.all(encodingQueue);
    console.log("All encoding tasks completed.");
  } catch (err) {
    console.error("Error during encoding:", err);
  }
};

encoder();

现在，我们有了一个名为 encoder 的函数，它正在运行。它的基本功能是创建一个名为 output_folder 的文件夹来存储编码文件，然后调用不同比特率的编码函数。因此，ffmpeg 运行不会立即给出结果，它有回调方法，我们必须等待它运行。因此，为了确认所有媒体都已编码，我们使用了 Javascript Promises。因此，一个编码任务将返回一个承诺，只有当所有承诺都完成时，我们才会打印 “所有编码任务已完成”。

现在，下一步就是分割这些已编码的视频。为此，我们将在代码中添加新内容。

const ffmpegStatic = require("ffmpeg-static");
const ffmpeg = require("fluent-ffmpeg");
const fs = require("fs");
const { exec } = require("child_process");

ffmpeg.setFfmpegPath(ffmpegStatic);

const bitrates = [
  {
    resolution: "1280x720",
    videoBitrate: "1500k",
    audioBitrate: "128k",
    outputName: "output_720p.mp4",
  },
  {
    resolution: "854x480",
    videoBitrate: "500k",
    audioBitrate: "96k",
    outputName: "output_480p.mp4",
  },
  {
    resolution: "640x360",
    videoBitrate: "250k",
    audioBitrate: "64k",
    outputName: "output_360p.mp4",
  },
];

const encodeVideo = (inputVideo, outputFolder, config) => {
  return new Promise((resolve, reject) => {
    ffmpeg(inputVideo)
      .videoCodec("libx264")
      .audioCodec("aac")
      .videoBitrate(config.videoBitrate)
      .audioBitrate(config.audioBitrate)
      .size(config.resolution)
      .output(`${outputFolder}/${config.outputName}`)
      .on("end", () => {
        console.log(`Finished encoding ${config.outputName}`);
        resolve(`${outputFolder}/${config.outputName}`);
      })
      .on("error", (err) => {
        console.error(`Error encoding ${config.outputName}: ${err}`);
        reject(err);
      })
      .run();
  });
};

const fragmentVideo = (inputVideo, outputFolder) => {
  return new Promise((resolve, reject) => {
    const strArr = inputVideo.split("/");
    const fragmentedVideoFile = `${outputFolder}/fragmented_${strArr[1]}`;
    const mp4fragmentCommand = `mp4fragment ${inputVideo} ${fragmentedVideoFile}`;
    exec(mp4fragmentCommand, (error, stdout, stderr) => {
      if (error) {
        console.error(`Error running mp4fragment: ${error.message}`);
        reject(stderr);
      }
      console.log(stdout);
      resolve(fragmentedVideoFile);
    });
  });
};

const encoder = async () => {
  const inputVideo = "input.mp4";
  const outputDirectory = "output_folder";
  const outputDirectoryFragment = "output_fragment";

  const permissions = 0o777;

  try {
    if (fs.existsSync(outputDirectory)) {
      fs.rmSync(outputDirectory, { recursive: true });
    }

    fs.mkdirSync(outputDirectory);
    fs.chmodSync(outputDirectory, permissions);

    const encodingQueue = [];

    for (const config of bitrates) {
      encodingQueue.push(encodeVideo(inputVideo, outputDirectory, config));
    }

    const outPutVideoFiles = await Promise.all(encodingQueue);
    console.log("All encoding tasks completed.");
    if (fs.existsSync(outputDirectoryFragment)) {
      fs.rmSync(outputDirectoryFragment, { recursive: true });
    }

    fs.mkdirSync(outputDirectoryFragment);
    fs.chmodSync(outputDirectoryFragment, permissions);

    const fragmentingQueue = [];

    for (const bitrateFile of outPutVideoFiles) {
      fragmentingQueue.push(
        fragmentVideo(bitrateFile, outputDirectoryFragment)
      );
    }

    const fragmentedFiles = await Promise.all(fragmentingQueue);
    console.log("All fragmenting tasks completed.");
  } catch (err) {
    console.error("Error during encoding:", err);
  }
};

encoder();

为此，我们直接在程序内部执行命令，并使用 “exec “来执行。所有视频编码完成后，我们会创建一个名为 output_fragment 的文件夹来存储分片文件并赋予权限。接下来，就像使用 Promise 编码一样，我要检查是否完成了所有分片工作。这就是 fragmenting 命令完成的简单任务。

mp4fragment INPUT_VIDEO OUTPUT_VIDEO

下一步是对分段视频进行 Dash 编码。这很简单，我们只需调用以下命令：

mp4dash --output-dir=OUTPUT_FOLDER FRAGMENTED_VIDEO1 FRAGMENTED_VIDEO2 ..

因此，代码将这样更改：

const ffmpegStatic = require("ffmpeg-static");
const ffmpeg = require("fluent-ffmpeg");
const fs = require("fs");
const { exec } = require("child_process");

ffmpeg.setFfmpegPath(ffmpegStatic);

const bitrates = [
  {
    resolution: "1280x720",
    videoBitrate: "1500k",
    audioBitrate: "128k",
    outputName: "output_720p.mp4",
  },
  {
    resolution: "854x480",
    videoBitrate: "500k",
    audioBitrate: "96k",
    outputName: "output_480p.mp4",
  },
  {
    resolution: "640x360",
    videoBitrate: "250k",
    audioBitrate: "64k",
    outputName: "output_360p.mp4",
  },
];

const encodeVideo = (inputVideo, outputFolder, config) => {
  return new Promise((resolve, reject) => {
    ffmpeg(inputVideo)
      .videoCodec("libx264")
      .audioCodec("aac")
      .videoBitrate(config.videoBitrate)
      .audioBitrate(config.audioBitrate)
      .size(config.resolution)
      .output(`${outputFolder}/${config.outputName}`)
      .on("end", () => {
        console.log(`Finished encoding ${config.outputName}`);
        resolve(`${outputFolder}/${config.outputName}`);
      })
      .on("error", (err) => {
        console.error(`Error encoding ${config.outputName}: ${err}`);
        reject(err);
      })
      .run();
  });
};

const fragmentVideo = (inputVideo, outputFolder) => {
  return new Promise((resolve, reject) => {
    const strArr = inputVideo.split("/");
    const fragmentedVideoFile = `${outputFolder}/fragmented_${strArr[1]}`;
    const mp4fragmentCommand = `mp4fragment ${inputVideo} ${fragmentedVideoFile}`;
    exec(mp4fragmentCommand, (error, stdout, stderr) => {
      if (error) {
        console.error(`Error running mp4fragment: ${error.message}`);
        reject(stderr);
      }
      console.log(stdout);
      resolve(fragmentedVideoFile);
    });
  });
};

const dashEncodeVideo = (fragmentedFiles, outputDirectory) => {
  return new Promise((resolve, reject) => {
    const mpdOutputFile = `${outputDirectory}/stream.mpd`;
    let mp4dashCommand = `mp4dash --output-dir=${outputDirectory}`;

    for (const fragmentedFile of fragmentedFiles) {
      mp4dashCommand = mp4dashCommand + ` ${fragmentedFile}`;
    }

    exec(mp4dashCommand, (error, stdout, stderr) => {
      if (error) {
        console.error(`Error running mp4dash: ${error.message}`);
        reject(stderr);
      }

      const mpdContent = fs.readFileSync(mpdOutputFile, "utf8");
      const dashManifest = `<?xml version="1.0" encoding="utf-8"?>
      <MPD xmlns="urn:mpeg:dash:schema:mpd:2011" minBufferTime="PT1.500S" profiles="urn:mpeg:dash:profile:isoff-live:2011" type="dynamic" mediaPresentationDuration="PT0H3M17.13S" maxSegmentDuration="PT0H0M4.800S">
        ${mpdContent}
      </MPD>`;

      const dashManifestFile = `${outputDirectory}/manifest.mpd`;
      fs.writeFileSync(dashManifestFile, dashManifest);
      resolve(dashManifest);
    });
  });
};

const encoder = async () => {
  const inputVideo = "input.mp4";
  const outputDirectory = "output_folder";
  const outputDirectoryDash = "output_dash";
  const outputDirectoryFragment = "output_fragment";

  const permissions = 0o777;

  try {
    if (fs.existsSync(outputDirectory)) {
      fs.rmSync(outputDirectory, { recursive: true });
    }

    fs.mkdirSync(outputDirectory);
    fs.chmodSync(outputDirectory, permissions);

    const encodingQueue = [];

    for (const config of bitrates) {
      encodingQueue.push(encodeVideo(inputVideo, outputDirectory, config));
    }

    const outPutVideoFiles = await Promise.all(encodingQueue);
    console.log("All encoding tasks completed.");
    if (fs.existsSync(outputDirectoryFragment)) {
      fs.rmSync(outputDirectoryFragment, { recursive: true });
    }

    fs.mkdirSync(outputDirectoryFragment);
    fs.chmodSync(outputDirectoryFragment, permissions);

    const fragmentingQueue = [];

    for (const bitrateFile of outPutVideoFiles) {
      fragmentingQueue.push(
        fragmentVideo(bitrateFile, outputDirectoryFragment)
      );
    }

    const fragmentedFiles = await Promise.all(fragmentingQueue);
    console.log("All fragmenting tasks completed.");

    if (fs.existsSync(outputDirectoryDash)) {
      fs.rmSync(outputDirectoryDash, { recursive: true });
    }
    const dashManifest = await dashEncodeVideo(
      fragmentedFiles,
      outputDirectoryDash
    );
    console.log("Encoding successfully completed");
    console.log(dashManifest);
  } catch (err) {
    console.error("Error during encoding:", err);
  }
};

encoder();

现在，如果运行这段代码，就会在控制台日志输出中看到最终的清单 mpd 文件。如果您参考之前的教程，我创建了一个 index.html 文件和一个 server.js 文件来渲染视频。使用该文件，您也可以在这里查看仪表盘格式的视频。

Github 代码：https://github.com/deBilla/bento-encoder

作者：Dimuthu Wickramanayake
源自：https://medium.com/nerd-for-tech/writing-a-video-encoder-using-node-js-ffmpeg-and-bento4-a4a04033dfa1