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import { VideoTranscodingFPS } from './video-transcoding-fps.model'
export enum VideoResolution {
H_240P = 240,
H_360P = 360,
H_480P = 480,
H_720P = 720,
H_1080P = 1080
}
/**
* 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 (tested with random music video): https://www.h3xed.com/blogmedia/youtube-info.php
*/
function getBaseBitrate (resolution: VideoResolution) {
switch (resolution) {
case VideoResolution.H_240P:
// quality according to Google Live Encoder: 300 - 700 Kbps
// Quality according to YouTube Video Info: 186 Kbps
return 250 * 1000
case VideoResolution.H_360P:
// quality according to Google Live Encoder: 400 - 1,000 Kbps
// Quality according to YouTube Video Info: 480 Kbps
return 500 * 1000
case VideoResolution.H_480P:
// quality according to Google Live Encoder: 500 - 2,000 Kbps
// Quality according to YouTube Video Info: 879 Kbps
return 900 * 1000
case VideoResolution.H_720P:
// quality according to Google Live Encoder: 1,500 - 4,000 Kbps
// Quality according to YouTube Video Info: 1752 Kbps
return 1750 * 1000
case VideoResolution.H_1080P: // fallthrough
default:
// quality according to Google Live Encoder: 3000 - 6000 Kbps
// Quality according to YouTube Video Info: 3277 Kbps
return 3300 * 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: VideoResolution, 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
}
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