75 lines
3 KiB
TypeScript
75 lines
3 KiB
TypeScript
import { VideoTranscodingFPS } from './video-transcoding-fps.model'
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export enum VideoResolution {
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H_240P = 240,
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H_360P = 360,
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H_480P = 480,
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H_720P = 720,
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H_1080P = 1080
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}
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/**
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* Bitrate targets for different resolutions, at VideoTranscodingFPS.AVERAGE.
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*
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* Sources for individual quality levels:
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* Google Live Encoder: https://support.google.com/youtube/answer/2853702?hl=en
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* YouTube Video Info (tested with random music video): https://www.h3xed.com/blogmedia/youtube-info.php
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*/
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function getBaseBitrate (resolution: VideoResolution) {
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switch (resolution) {
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case VideoResolution.H_240P:
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// quality according to Google Live Encoder: 300 - 700 Kbps
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// Quality according to YouTube Video Info: 186 Kbps
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return 250 * 1000
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case VideoResolution.H_360P:
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// quality according to Google Live Encoder: 400 - 1,000 Kbps
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// Quality according to YouTube Video Info: 480 Kbps
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return 500 * 1000
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case VideoResolution.H_480P:
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// quality according to Google Live Encoder: 500 - 2,000 Kbps
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// Quality according to YouTube Video Info: 879 Kbps
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return 900 * 1000
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case VideoResolution.H_720P:
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// quality according to Google Live Encoder: 1,500 - 4,000 Kbps
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// Quality according to YouTube Video Info: 1752 Kbps
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return 1750 * 1000
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case VideoResolution.H_1080P: // fallthrough
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default:
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// quality according to Google Live Encoder: 3000 - 6000 Kbps
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// Quality according to YouTube Video Info: 3277 Kbps
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return 3300 * 1000
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}
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}
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/**
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* Calculate the target bitrate based on video resolution and FPS.
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*
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* The calculation is based on two values:
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* Bitrate at VideoTranscodingFPS.AVERAGE is always the same as
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* getBaseBitrate(). Bitrate at VideoTranscodingFPS.MAX is always
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* getBaseBitrate() * 1.4. All other values are calculated linearly
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* between these two points.
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*/
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export function getTargetBitrate (resolution: VideoResolution, fps: number, fpsTranscodingConstants: VideoTranscodingFPS) {
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const baseBitrate = getBaseBitrate(resolution)
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// The maximum bitrate, used when fps === VideoTranscodingFPS.MAX
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// Based on numbers from Youtube, 60 fps bitrate divided by 30 fps bitrate:
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// 720p: 2600 / 1750 = 1.49
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// 1080p: 4400 / 3300 = 1.33
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const maxBitrate = baseBitrate * 1.4
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const maxBitrateDifference = maxBitrate - baseBitrate
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const maxFpsDifference = fpsTranscodingConstants.MAX - fpsTranscodingConstants.AVERAGE
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// For 1080p video with default settings, this results in the following formula:
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// 3300 + (x - 30) * (1320/30)
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// Example outputs:
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// 1080p10: 2420 kbps, 1080p30: 3300 kbps, 1080p60: 4620 kbps
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// 720p10: 1283 kbps, 720p30: 1750 kbps, 720p60: 2450 kbps
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return baseBitrate + (fps - fpsTranscodingConstants.AVERAGE) * (maxBitrateDifference / maxFpsDifference)
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}
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/**
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* The maximum bitrate we expect to see on a transcoded video in bytes per second.
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*/
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export function getMaxBitrate (resolution: VideoResolution, fps: number, fpsTranscodingConstants: VideoTranscodingFPS) {
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return getTargetBitrate(resolution, fps, fpsTranscodingConstants) * 2
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}
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