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

   1 import { VideoTranscodingFPS } from './video-transcoding-fps.model'
   2
   3 export const 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: number) {
  21   if (resolution === VideoResolution.H_NOVIDEO) {
  22     // audio-only
  23     return 64 * 1000
  24   }
  25
  26   if (resolution <= 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
  32   if (resolution <= VideoResolution.H_360P) {
  33     // quality according to Google Live Encoder: 400 - 1,000 Kbps
  34     // Quality according to YouTube Video Info: 700 Kbps
  35     return 780 * 1000
  36   }
  37
  38   if (resolution <= VideoResolution.H_480P) {
  39     // quality according to Google Live Encoder: 500 - 2,000 Kbps
  40     // Quality according to YouTube Video Info: 1300 Kbps
  41     return 1500 * 1000
  42   }
  43
  44   if (resolution <= VideoResolution.H_720P) {
  45     // quality according to Google Live Encoder: 1,500 - 4,000 Kbps
  46     // Quality according to YouTube Video Info: 2680 Kbps
  47     return 2800 * 1000
  48   }
  49
  50   if (resolution <= VideoResolution.H_1080P) {
  51     // quality according to Google Live Encoder: 3000 - 6000 Kbps
  52     // Quality according to YouTube Video Info: 5081 Kbps
  53     return 5200 * 1000
  54   }
  55
  56   // 4K
  57   // quality according to Google Live Encoder: 13000 - 34000 Kbps
  58   return 22000 * 1000
  59 }
  60
  61 /**
  62  * Calculate the target bitrate based on video resolution and FPS.
  63  *
  64  * The calculation is based on two values:
  65  * Bitrate at VideoTranscodingFPS.AVERAGE is always the same as
  66  * getBaseBitrate(). Bitrate at VideoTranscodingFPS.MAX is always
  67  * getBaseBitrate() * 1.4. All other values are calculated linearly
  68  * between these two points.
  69  */
  70 export function getTargetBitrate (resolution: number, fps: number, fpsTranscodingConstants: VideoTranscodingFPS) {
  71   const baseBitrate = getBaseBitrate(resolution)
  72   // The maximum bitrate, used when fps === VideoTranscodingFPS.MAX
  73   // Based on numbers from Youtube, 60 fps bitrate divided by 30 fps bitrate:
  74   //  720p: 2600 / 1750 = 1.49
  75   // 1080p: 4400 / 3300 = 1.33
  76   const maxBitrate = baseBitrate * 1.4
  77   const maxBitrateDifference = maxBitrate - baseBitrate
  78   const maxFpsDifference = fpsTranscodingConstants.MAX - fpsTranscodingConstants.AVERAGE
  79   // For 1080p video with default settings, this results in the following formula:
  80   // 3300 + (x - 30) * (1320/30)
  81   // Example outputs:
  82   // 1080p10: 2420 kbps, 1080p30: 3300 kbps, 1080p60: 4620 kbps
  83   //  720p10: 1283 kbps,  720p30: 1750 kbps,  720p60: 2450 kbps
  84   return Math.floor(baseBitrate + (fps - fpsTranscodingConstants.AVERAGE) * (maxBitrateDifference / maxFpsDifference))
  85 }
  86
  87 /**
  88  * The maximum bitrate we expect to see on a transcoded video in bytes per second.
  89  */
  90 export function getMaxBitrate (resolution: VideoResolution, fps: number, fpsTranscodingConstants: VideoTranscodingFPS) {
  91   return getTargetBitrate(resolution, fps, fpsTranscodingConstants) * 2
  92 }