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Scale bitrate linearly with FPS

pull/1296/head
Felix Ableitner 2018-10-09 17:46:26 -05:00 committed by Chocobozzz
parent 7cdc3ab63b
commit 7f196c9320
1 changed files with 22 additions and 15 deletions
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37
shared/models/videos/video-resolution.enum.ts
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@ -9,13 +9,13 @@ export enum VideoResolution {
}
/**
* Bitrate targets for different resolutions and frame rates, in bytes per second.
* 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
*/
export function getTargetBitrate (resolution: VideoResolution, fps: number,
fpsTranscodingConstants: VideoTranscodingFPS) {
export function getBaseBitrate (resolution: VideoResolution) {
switch (resolution) {
case VideoResolution.H_240P:
// quality according to Google Live Encoder: 300 - 700 Kbps
@ -30,29 +30,36 @@ export function getTargetBitrate (resolution: VideoResolution, fps: number,
// Quality according to YouTube Video Info: 879 Kbps
return 900 * 1000
case VideoResolution.H_720P:
if (fps === fpsTranscodingConstants.MAX) {
// quality according to Google Live Encoder: 2,250 - 6,000 Kbps
// Quality according to YouTube Video Info: 2634 Kbps
return 2600 * 1000
}
// 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:
if (fps === fpsTranscodingConstants.MAX) {
// quality according to Google Live Encoder: 3000 - 6000 Kbps
// Quality according to YouTube Video Info: 4387 Kbps
return 4400 * 1000
}
// 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.
*/
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:
// 2600 / 1750 = 1.48571428571
// 4400 / 3300 = 1.33333333333
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: 1080p30: 3300 kbps, 1080p60: 4620 kbps, 720p30: 1750, 720p60: 2450
return baseBitrate + (fps - fpsTranscodingConstants.AVERAGE) * (maxBitrateDifference / maxFpsDifference)
}
/**
* The maximum bitrate we expect to see on a transcoded video in bytes per second.
*/