1 files changed, 68 insertions, 0 deletions

diff --git a/shared/models/videos/video-resolution.enum.ts b/shared/models/videos/video-resolution.enum.ts
index 100fc0e6e..7da5e7100 100644
--- a/shared/models/videos/video-resolution.enum.ts
+++ b/shared/models/videos/video-resolution.enum.ts
@@ -1,3 +1,5 @@
+import { VideoTranscodingFPS } from './video-transcoding-fps.model'
+
 export enum VideoResolution {
   H_240P = 240,
   H_360P = 360,
@@ -5,3 +7,69 @@ export enum VideoResolution {
   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
+}