From ff7629aba5a519afd590259853cf2651c5b39445 Mon Sep 17 00:00:00 2001
From: samrobinson <samrobinson@google.com>
Date: Fri, 6 May 2022 16:03:18 +0100
Subject: [PATCH] Match the suggested bitrate to the actual Kush Gauge formula.

As defined in Kush Amerasinghe's paper 'H.264 For the rest of us'.

PiperOrigin-RevId: 446988272
---
 .../transformer/DefaultEncoderFactory.java    | 19 ++++++++++++++++---
 .../DefaultEncoderFactoryTest.java            |  8 ++++----
 2 files changed, 20 insertions(+), 7 deletions(-)

diff --git a/libraries/transformer/src/main/java/androidx/media3/transformer/DefaultEncoderFactory.java b/libraries/transformer/src/main/java/androidx/media3/transformer/DefaultEncoderFactory.java
index 5ec10391ec..ff638e8eb8 100644
--- a/libraries/transformer/src/main/java/androidx/media3/transformer/DefaultEncoderFactory.java
+++ b/libraries/transformer/src/main/java/androidx/media3/transformer/DefaultEncoderFactory.java
@@ -504,11 +504,24 @@ public final class DefaultEncoderFactory implements Codec.EncoderFactory {
         && allowedMimeTypes.contains(mimeType);
   }
 
-  /** Computes the video bit rate using the Kush Gauge. */
+  /**
+   * Computes the video bit rate using the Kush Gauge.
+   *
+   * <p>{@code kushGaugeBitrate = height * width * frameRate * 0.07 * motionFactor}.
+   *
+   * <p>Motion factors:
+   *
+   * <ul>
+   *   <li>Low motion video - 1
+   *   <li>Medium motion video - 2
+   *   <li>High motion video - 4
+   * </ul>
+   */
   private static int getSuggestedBitrate(int width, int height, float frameRate) {
     // TODO(b/210591626) Implement bitrate estimation.
-    // 1080p30 -> 6.2Mbps, 720p30 -> 2.7Mbps.
-    return (int) (width * height * frameRate * 0.1);
+    // Assume medium motion factor.
+    // 1080p60 -> 16.6Mbps, 720p30 -> 3.7Mbps.
+    return (int) (width * height * frameRate * 0.07 * 2);
   }
 
   @RequiresNonNull("#1.sampleMimeType")
diff --git a/libraries/transformer/src/test/java/androidx/media3/transformer/DefaultEncoderFactoryTest.java b/libraries/transformer/src/test/java/androidx/media3/transformer/DefaultEncoderFactoryTest.java
index 6fd88d043b..4078e3eeb4 100644
--- a/libraries/transformer/src/test/java/androidx/media3/transformer/DefaultEncoderFactoryTest.java
+++ b/libraries/transformer/src/test/java/androidx/media3/transformer/DefaultEncoderFactoryTest.java
@@ -74,8 +74,8 @@ public class DefaultEncoderFactoryTest {
     assertThat(actualVideoFormat.sampleMimeType).isEqualTo(MimeTypes.VIDEO_H264);
     assertThat(actualVideoFormat.width).isEqualTo(1920);
     assertThat(actualVideoFormat.height).isEqualTo(1080);
-    // 1920 * 1080 * 30 * 0.1
-    assertThat(actualVideoFormat.averageBitrate).isEqualTo(6_220_800);
+    // 1920 * 1080 * 30 * 0.07 * 2.
+    assertThat(actualVideoFormat.averageBitrate).isEqualTo(8_709_120);
   }
 
   @Test
@@ -92,8 +92,8 @@ public class DefaultEncoderFactoryTest {
     assertThat(actualVideoFormat.sampleMimeType).isEqualTo(MimeTypes.VIDEO_H264);
     assertThat(actualVideoFormat.width).isEqualTo(1920);
     assertThat(actualVideoFormat.height).isEqualTo(1080);
-    // 1920 * 1080 * 30 * 0.1
-    assertThat(actualVideoFormat.averageBitrate).isEqualTo(6_220_800);
+    // 1920 * 1080 * 30 * 0.07 * 2.
+    assertThat(actualVideoFormat.averageBitrate).isEqualTo(8_709_120);
   }
 
   @Test