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1 | import { VideoTranscodingFPS } from './video-transcoding-fps.model' | |
2 | ||
3 | export const enum VideoResolution { | |
4 | H_NOVIDEO = 0, | |
5 | H_240P = 240, | |
6 | H_360P = 360, | |
7 | H_480P = 480, | |
8 | H_720P = 720, | |
9 | H_1080P = 1080, | |
10 | H_1440P = 1440, | |
11 | H_4K = 2160 | |
12 | } | |
13 | ||
14 | /** | |
15 | * Bitrate targets for different resolutions, at VideoTranscodingFPS.AVERAGE. | |
16 | * | |
17 | * Sources for individual quality levels: | |
18 | * Google Live Encoder: https://support.google.com/youtube/answer/2853702?hl=en | |
19 | * YouTube Video Info: youtube-dl --list-formats, with sample videos | |
20 | */ | |
21 | function getBaseBitrate (resolution: number) { | |
22 | if (resolution === VideoResolution.H_NOVIDEO) { | |
23 | // audio-only | |
24 | return 64 * 1000 | |
25 | } | |
26 | ||
27 | if (resolution <= VideoResolution.H_240P) { | |
28 | // quality according to Google Live Encoder: 300 - 700 Kbps | |
29 | // Quality according to YouTube Video Info: 285 Kbps | |
30 | return 320 * 1000 | |
31 | } | |
32 | ||
33 | if (resolution <= VideoResolution.H_360P) { | |
34 | // quality according to Google Live Encoder: 400 - 1,000 Kbps | |
35 | // Quality according to YouTube Video Info: 700 Kbps | |
36 | return 780 * 1000 | |
37 | } | |
38 | ||
39 | if (resolution <= VideoResolution.H_480P) { | |
40 | // quality according to Google Live Encoder: 500 - 2,000 Kbps | |
41 | // Quality according to YouTube Video Info: 1300 Kbps | |
42 | return 1500 * 1000 | |
43 | } | |
44 | ||
45 | if (resolution <= VideoResolution.H_720P) { | |
46 | // quality according to Google Live Encoder: 1,500 - 4,000 Kbps | |
47 | // Quality according to YouTube Video Info: 2680 Kbps | |
48 | return 2800 * 1000 | |
49 | } | |
50 | ||
51 | if (resolution <= VideoResolution.H_1080P) { | |
52 | // quality according to Google Live Encoder: 3000 - 6000 Kbps | |
53 | // Quality according to YouTube Video Info: 5081 Kbps | |
54 | return 5200 * 1000 | |
55 | } | |
56 | ||
57 | if (resolution <= VideoResolution.H_1440P) { | |
58 | // quality according to Google Live Encoder: 6000 - 13000 Kbps | |
59 | // Quality according to YouTube Video Info: 8600 (av01) - 17000 (vp9.2) Kbps | |
60 | return 10_000 * 1000 | |
61 | } | |
62 | ||
63 | // 4K | |
64 | // quality according to Google Live Encoder: 13000 - 34000 Kbps | |
65 | return 22_000 * 1000 | |
66 | } | |
67 | ||
68 | /** | |
69 | * Calculate the target bitrate based on video resolution and FPS. | |
70 | * | |
71 | * The calculation is based on two values: | |
72 | * Bitrate at VideoTranscodingFPS.AVERAGE is always the same as | |
73 | * getBaseBitrate(). Bitrate at VideoTranscodingFPS.MAX is always | |
74 | * getBaseBitrate() * 1.4. All other values are calculated linearly | |
75 | * between these two points. | |
76 | */ | |
77 | export function getTargetBitrate (resolution: number, fps: number, fpsTranscodingConstants: VideoTranscodingFPS) { | |
78 | const baseBitrate = getBaseBitrate(resolution) | |
79 | // The maximum bitrate, used when fps === VideoTranscodingFPS.MAX | |
80 | // Based on numbers from Youtube, 60 fps bitrate divided by 30 fps bitrate: | |
81 | // 720p: 2600 / 1750 = 1.49 | |
82 | // 1080p: 4400 / 3300 = 1.33 | |
83 | const maxBitrate = baseBitrate * 1.4 | |
84 | const maxBitrateDifference = maxBitrate - baseBitrate | |
85 | const maxFpsDifference = fpsTranscodingConstants.MAX - fpsTranscodingConstants.AVERAGE | |
86 | // For 1080p video with default settings, this results in the following formula: | |
87 | // 3300 + (x - 30) * (1320/30) | |
88 | // Example outputs: | |
89 | // 1080p10: 2420 kbps, 1080p30: 3300 kbps, 1080p60: 4620 kbps | |
90 | // 720p10: 1283 kbps, 720p30: 1750 kbps, 720p60: 2450 kbps | |
91 | return Math.floor(baseBitrate + (fps - fpsTranscodingConstants.AVERAGE) * (maxBitrateDifference / maxFpsDifference)) | |
92 | } | |
93 | ||
94 | /** | |
95 | * The maximum bitrate we expect to see on a transcoded video in bytes per second. | |
96 | */ | |
97 | export function getMaxBitrate (resolution: VideoResolution, fps: number, fpsTranscodingConstants: VideoTranscodingFPS) { | |
98 | return getTargetBitrate(resolution, fps, fpsTranscodingConstants) * 2 | |
99 | } |