+import { VideoTranscodingFPS } from './video-transcoding-fps.model'
+
export enum VideoResolution {
H_240P = 240,
H_360P = 360,
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
+}