shared/models/videos/video-resolution.enum.ts

   1 import { VideoTranscodingFPS } from './video-transcoding-fps.model'
   2
   3 export enum VideoResolution {
   4   H_NOVIDEO = 0,
   5   H_240P = 240,
   6   H_360P = 360,
   7   H_480P = 480,
   8   H_720P = 720,
   9   H_1080P = 1080,
  10   H_4K = 2160
  11 }
  12
  13 /**
  14  * Bitrate targets for different resolutions, at VideoTranscodingFPS.AVERAGE.
  15  *
  16  * Sources for individual quality levels:
  17  * Google Live Encoder: https://support.google.com/youtube/answer/2853702?hl=en
  18  * YouTube Video Info: youtube-dl --list-formats, with sample videos
  19  */
  20 function getBaseBitrate (resolution: VideoResolution) {
  21   switch (resolution) {
  22     case VideoResolution.H_NOVIDEO:
  23       // audio-only
  24       return 64 * 1000
  25
  26     case VideoResolution.H_240P:
  27       // quality according to Google Live Encoder: 300 - 700 Kbps
  28       // Quality according to YouTube Video Info: 285 Kbps
  29       return 320 * 1000
  30
  31     case VideoResolution.H_360P:
  32       // quality according to Google Live Encoder: 400 - 1,000 Kbps
  33       // Quality according to YouTube Video Info: 700 Kbps
  34       return 780 * 1000
  35
  36     case VideoResolution.H_480P:
  37       // quality according to Google Live Encoder: 500 - 2,000 Kbps
  38       // Quality according to YouTube Video Info: 1300 Kbps
  39       return 1500 * 1000
  40
  41     case VideoResolution.H_720P:
  42       // quality according to Google Live Encoder: 1,500 - 4,000 Kbps
  43       // Quality according to YouTube Video Info: 2680 Kbps
  44       return 2800 * 1000
  45
  46     case VideoResolution.H_1080P:
  47       // quality according to Google Live Encoder: 3000 - 6000 Kbps
  48       // Quality according to YouTube Video Info: 5081 Kbps
  49       return 5800 * 1000
  50
  51     case VideoResolution.H_4K: // fallthrough
  52     default:
  53       // quality according to Google Live Encoder: 13000 - 34000 Kbps
  54       return 15000 * 1000
  55   }
  56 }
  57
  58 /**
  59  * Calculate the target bitrate based on video resolution and FPS.
  60  *
  61  * The calculation is based on two values:
  62  * Bitrate at VideoTranscodingFPS.AVERAGE is always the same as
  63  * getBaseBitrate(). Bitrate at VideoTranscodingFPS.MAX is always
  64  * getBaseBitrate() * 1.4. All other values are calculated linearly
  65  * between these two points.
  66  */
  67 export function getTargetBitrate (resolution: VideoResolution, fps: number, fpsTranscodingConstants: VideoTranscodingFPS) {
  68   const baseBitrate = getBaseBitrate(resolution)
  69   // The maximum bitrate, used when fps === VideoTranscodingFPS.MAX
  70   // Based on numbers from Youtube, 60 fps bitrate divided by 30 fps bitrate:
  71   //  720p: 2600 / 1750 = 1.49
  72   // 1080p: 4400 / 3300 = 1.33
  73   const maxBitrate = baseBitrate * 1.4
  74   const maxBitrateDifference = maxBitrate - baseBitrate
  75   const maxFpsDifference = fpsTranscodingConstants.MAX - fpsTranscodingConstants.AVERAGE
  76   // For 1080p video with default settings, this results in the following formula:
  77   // 3300 + (x - 30) * (1320/30)
  78   // Example outputs:
  79   // 1080p10: 2420 kbps, 1080p30: 3300 kbps, 1080p60: 4620 kbps
  80   //  720p10: 1283 kbps,  720p30: 1750 kbps,  720p60: 2450 kbps
  81   return baseBitrate + (fps - fpsTranscodingConstants.AVERAGE) * (maxBitrateDifference / maxFpsDifference)
  82 }
  83
  84 /**
  85  * The maximum bitrate we expect to see on a transcoded video in bytes per second.
  86  */
  87 export function getMaxBitrate (resolution: VideoResolution, fps: number, fpsTranscodingConstants: VideoTranscodingFPS) {
  88   return getTargetBitrate(resolution, fps, fpsTranscodingConstants) * 2
  89 }