1 files changed, 30 insertions, 15 deletions

diff --git a/shared/models/videos/video-resolution.enum.ts b/shared/models/videos/video-resolution.enum.ts
index e40e5b58b..2eee03843 100644
--- a/shared/models/videos/video-resolution.enum.ts
+++ b/shared/models/videos/video-resolution.enum.ts
@@ -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) {
+function getBaseBitrate (resolution: VideoResolution) {
   switch (resolution) {
   case VideoResolution.H_240P:
     // quality according to Google Live Encoder: 300 - 700 Kbps
@@ -30,23 +30,11 @@ 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
@@ -54,6 +42,33 @@ export function getTargetBitrate (resolution: VideoResolution, fps: number,
 }
 
 /**
+ * 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,