generate-captions.js

const base = {
  "timeline": {
    "cache": false,
    "background": "#000000",
    "fonts": [{
      "src": "https://shotstack-assets.s3.amazonaws.com/fonts/NotoSans-Regular.ttf"
    }],
    "tracks": [
      {
        "clips": []
      },
      {
        "clips": [{
          "asset": {
            "type": "",
            "src": "",
            "volume": 1
          },
          "start": 0,
          "length": 0
        }]
      }
    ]
  },
  "output": {
    "format": "mp4",
    "size": {
      "width": 1280,
      "height": 720
    },
    "destinations": [{
      "provider": "shotstack",
      "exclude": true
    }]
  }
};

module.exports.generateTemplate = async (videoWidth, videoHeight, url, duration, captions) => {
  let clip;
  let fontSize;

  if (videoHeight >= videoWidth) {
    if (videoHeight <= 720) fontSize = 24;
    if (videoHeight <= 1080) fontSize = 36;
    if (videoHeight > 1080) fontSize = 48;
  } else {
    if (videoHeight <= 720) fontSize = 28;
    if (videoHeight <= 1080) fontSize = 40;
    if (videoHeight > 1080) fontSize = 52;
  }

  const clips = [];

  for (let i = 0; i < captions.length; i += 1) {
    const wordCount = captions[i].text.split(' ').length;
    let heightScale;
    if (wordCount <= 20) {
      heightScale = 1;
    } else if (wordCount > 20 && wordCount <= 32) {
      heightScale = 1.25;
    } else if (wordCount > 32 && wordCount <= 45) {
      heightScale = 1.5;
    } else if (wordCount > 45 && wordCount <= 60) {
      heightScale = 1.75;
    } else if (wordCount > 60) {
      heightScale = 2;
    }
    clip.asset.html = `<span>${captions[i].text}</span>`;
    clip.start = captions[i].start;
    clip.length = captions[i].length - (1 / 25);
    clips.push(clip);
  }
  base.timeline.tracks[0].clips.push(...clips);
  base.timeline.tracks[1].clips[0].asset.type = 'video';
  base.timeline.tracks[1].clips[0].asset.src = videoUrl;
  base.timeline.tracks[1].clips[0].length = duration;
  if (videoHeight <= 2180) {
    base.output.size.width = videoWidth;
    base.output.size.height = videoHeight;
  } else {
    base.output.size.width = 3840;
    base.output.size.height = 2180;
  }
  return base;
};