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

   1 import { VideoTranscodingFPS } from './video-transcoding-fps.model'
   2
   3 export enum VideoResolution {
   4   H_240P = 240,
   5   H_360P = 360,
   6   H_480P = 480,
   7   H_720P = 720,
   8   H_1080P = 1080,
   9   H_4K = 2160
  10 }
  11
  12 /**
  13  * Bitrate targets for different resolutions, at VideoTranscodingFPS.AVERAGE.
  14  *
  15  * Sources for individual quality levels:
  16  * Google Live Encoder: https://support.google.com/youtube/answer/2853702?hl=en
  17  * YouTube Video Info (tested with random music video): https://www.h3xed.com/blogmedia/youtube-info.php
  18  */
  19 function getBaseBitrate (resolution: VideoResolution) {
  20   switch (resolution) {
  21   case VideoResolution.H_240P:
  22     // quality according to Google Live Encoder: 300 - 700 Kbps
  23     // Quality according to YouTube Video Info: 186 Kbps
  24     return 250 * 1000
  25   case VideoResolution.H_360P:
  26     // quality according to Google Live Encoder: 400 - 1,000 Kbps
  27     // Quality according to YouTube Video Info: 480 Kbps
  28     return 500 * 1000
  29   case VideoResolution.H_480P:
  30     // quality according to Google Live Encoder: 500 - 2,000 Kbps
  31     // Quality according to YouTube Video Info: 879 Kbps
  32     return 900 * 1000
  33   case VideoResolution.H_720P:
  34     // quality according to Google Live Encoder: 1,500 - 4,000 Kbps
  35     // Quality according to YouTube Video Info: 1752 Kbps
  36     return 1750 * 1000
  37   case VideoResolution.H_1080P:
  38     // quality according to Google Live Encoder: 3000 - 6000 Kbps
  39     // Quality according to YouTube Video Info: 3277 Kbps
  40     return 3300 * 1000
  41   case VideoResolution.H_4K: // fallthrough
  42   default:
  43     // quality according to Google Live Encoder: 13000 - 34000 Kbps
  44     return 15000 * 1000
  45   }
  46 }
  47
  48 /**
  49  * Calculate the target bitrate based on video resolution and FPS.
  50  *
  51  * The calculation is based on two values:
  52  * Bitrate at VideoTranscodingFPS.AVERAGE is always the same as
  53  * getBaseBitrate(). Bitrate at VideoTranscodingFPS.MAX is always
  54  * getBaseBitrate() * 1.4. All other values are calculated linearly
  55  * between these two points.
  56  */
  57 export function getTargetBitrate (resolution: VideoResolution, fps: number, fpsTranscodingConstants: VideoTranscodingFPS) {
  58   const baseBitrate = getBaseBitrate(resolution)
  59   // The maximum bitrate, used when fps === VideoTranscodingFPS.MAX
  60   // Based on numbers from Youtube, 60 fps bitrate divided by 30 fps bitrate:
  61   //  720p: 2600 / 1750 = 1.49
  62   // 1080p: 4400 / 3300 = 1.33
  63   const maxBitrate = baseBitrate * 1.4
  64   const maxBitrateDifference = maxBitrate - baseBitrate
  65   const maxFpsDifference = fpsTranscodingConstants.MAX - fpsTranscodingConstants.AVERAGE
  66   // For 1080p video with default settings, this results in the following formula:
  67   // 3300 + (x - 30) * (1320/30)
  68   // Example outputs:
  69   // 1080p10: 2420 kbps, 1080p30: 3300 kbps, 1080p60: 4620 kbps
  70   //  720p10: 1283 kbps,  720p30: 1750 kbps,  720p60: 2450 kbps
  71   return baseBitrate + (fps - fpsTranscodingConstants.AVERAGE) * (maxBitrateDifference / maxFpsDifference)
  72 }
  73
  74 /**
  75  * The maximum bitrate we expect to see on a transcoded video in bytes per second.
  76  */
  77 export function getMaxBitrate (resolution: VideoResolution, fps: number, fpsTranscodingConstants: VideoTranscodingFPS) {
  78   return getTargetBitrate(resolution, fps, fpsTranscodingConstants) * 2
  79 }