import { VideoTranscodingFPS } from './video-transcoding-fps.model' export const enum VideoResolution { H_NOVIDEO = 0, H_240P = 240, H_360P = 360, H_480P = 480, H_720P = 720, H_1080P = 1080, H_4K = 2160 } /** * Bitrate targets for different resolutions, at VideoTranscodingFPS.AVERAGE. * * Sources for individual quality levels: * Google Live Encoder: https://support.google.com/youtube/answer/2853702?hl=en * YouTube Video Info: youtube-dl --list-formats, with sample videos */ function getBaseBitrate (resolution: number) { if (resolution === VideoResolution.H_NOVIDEO) { // audio-only return 64 * 1000 } if (resolution <= VideoResolution.H_240P) { // quality according to Google Live Encoder: 300 - 700 Kbps // Quality according to YouTube Video Info: 285 Kbps return 320 * 1000 } if (resolution <= VideoResolution.H_360P) { // quality according to Google Live Encoder: 400 - 1,000 Kbps // Quality according to YouTube Video Info: 700 Kbps return 780 * 1000 } if (resolution <= VideoResolution.H_480P) { // quality according to Google Live Encoder: 500 - 2,000 Kbps // Quality according to YouTube Video Info: 1300 Kbps return 1500 * 1000 } if (resolution <= VideoResolution.H_720P) { // quality according to Google Live Encoder: 1,500 - 4,000 Kbps // Quality according to YouTube Video Info: 2680 Kbps return 2800 * 1000 } if (resolution <= VideoResolution.H_1080P) { // quality according to Google Live Encoder: 3000 - 6000 Kbps // Quality according to YouTube Video Info: 5081 Kbps return 5200 * 1000 } // 4K // quality according to Google Live Encoder: 13000 - 34000 Kbps return 22000 * 1000 } /** * Calculate the target bitrate based on video resolution and FPS. * * The calculation is based on two values: * Bitrate at VideoTranscodingFPS.AVERAGE is always the same as * getBaseBitrate(). Bitrate at VideoTranscodingFPS.MAX is always * getBaseBitrate() * 1.4. All other values are calculated linearly * between these two points. */ export function getTargetBitrate (resolution: number, fps: number, fpsTranscodingConstants: VideoTranscodingFPS) { const baseBitrate = getBaseBitrate(resolution) // The maximum bitrate, used when fps === VideoTranscodingFPS.MAX // Based on numbers from Youtube, 60 fps bitrate divided by 30 fps bitrate: // 720p: 2600 / 1750 = 1.49 // 1080p: 4400 / 3300 = 1.33 const maxBitrate = baseBitrate * 1.4 const maxBitrateDifference = maxBitrate - baseBitrate const maxFpsDifference = fpsTranscodingConstants.MAX - fpsTranscodingConstants.AVERAGE // For 1080p video with default settings, this results in the following formula: // 3300 + (x - 30) * (1320/30) // Example outputs: // 1080p10: 2420 kbps, 1080p30: 3300 kbps, 1080p60: 4620 kbps // 720p10: 1283 kbps, 720p30: 1750 kbps, 720p60: 2450 kbps return baseBitrate + (fps - fpsTranscodingConstants.AVERAGE) * (maxBitrateDifference / maxFpsDifference) } /** * The maximum bitrate we expect to see on a transcoded video in bytes per second. */ export function getMaxBitrate (resolution: VideoResolution, fps: number, fpsTranscodingConstants: VideoTranscodingFPS) { return getTargetBitrate(resolution, fps, fpsTranscodingConstants) * 2 }