Use the true bitrate for CBR MP3 seeking

PiperOrigin-RevId: 225989898

RELEASENOTES.md

@@ -7,6 +7,7 @@
 * Support for playing spherical videos on Daydream.
 * Improve decoder re-use between playbacks. TODO: Write and link a blog post
   here ([#2826](https://github.com/google/ExoPlayer/issues/2826)).
+* Use the true bitrate for constant-bitrate MP3 seeking.
 * Track selection:
   * Add options for controlling audio track selections to `DefaultTrackSelector`
     ([#3314](https://github.com/google/ExoPlayer/issues/3314)).

library/core/src/main/java/com/google/android/exoplayer2/extractor/MpegAudioHeader.java

@@ -34,16 +34,26 @@ public final class MpegAudioHeader {
   private static final String[] MIME_TYPE_BY_LAYER =
       new String[] {MimeTypes.AUDIO_MPEG_L1, MimeTypes.AUDIO_MPEG_L2, MimeTypes.AUDIO_MPEG};
   private static final int[] SAMPLING_RATE_V1 = {44100, 48000, 32000};
-  private static final int[] BITRATE_V1_L1 =
+  private static final int[] BITRATE_V1_L1 = {
-      {32, 64, 96, 128, 160, 192, 224, 256, 288, 320, 352, 384, 416, 448};
+    32000, 64000, 96000, 128000, 160000, 192000, 224000, 256000, 288000, 320000, 352000, 384000,
-  private static final int[] BITRATE_V2_L1 =
+    416000, 448000
-      {32, 48, 56, 64, 80, 96, 112, 128, 144, 160, 176, 192, 224, 256};
+  };
-  private static final int[] BITRATE_V1_L2 =
+  private static final int[] BITRATE_V2_L1 = {
-      {32, 48, 56, 64, 80, 96, 112, 128, 160, 192, 224, 256, 320, 384};
+    32000, 48000, 56000, 64000, 80000, 96000, 112000, 128000, 144000, 160000, 176000, 192000,
-  private static final int[] BITRATE_V1_L3 =
+    224000, 256000
-      {32, 40, 48, 56, 64, 80, 96, 112, 128, 160, 192, 224, 256, 320};
+  };
-  private static final int[] BITRATE_V2 =
+  private static final int[] BITRATE_V1_L2 = {
-      {8, 16, 24, 32, 40, 48, 56, 64, 80, 96, 112, 128, 144, 160};
+    32000, 48000, 56000, 64000, 80000, 96000, 112000, 128000, 160000, 192000, 224000, 256000,
+    320000, 384000
+  };
+  private static final int[] BITRATE_V1_L3 = {
+    32000, 40000, 48000, 56000, 64000, 80000, 96000, 112000, 128000, 160000, 192000, 224000, 256000,
+    320000
+  };
+  private static final int[] BITRATE_V2 = {
+    8000, 16000, 24000, 32000, 40000, 48000, 56000, 64000, 80000, 96000, 112000, 128000, 144000,
+    160000
+  };
 
   /**
    * Returns the size of the frame associated with {@code header}, or {@link C#LENGTH_UNSET} if it
@@ -89,7 +99,7 @@ public final class MpegAudioHeader {
     if (layer == 3) {
       // Layer I (layer == 3)
       bitrate = version == 3 ? BITRATE_V1_L1[bitrateIndex - 1] : BITRATE_V2_L1[bitrateIndex - 1];
-      return (12000 * bitrate / samplingRate + padding) * 4;
+      return (12 * bitrate / samplingRate + padding) * 4;
     } else {
       // Layer II (layer == 2) or III (layer == 1)
       if (version == 3) {
@@ -102,10 +112,10 @@ public final class MpegAudioHeader {
 
     if (version == 3) {
       // Version 1
-      return 144000 * bitrate / samplingRate + padding;
+      return 144 * bitrate / samplingRate + padding;
     } else {
       // Version 2 or 2.5
-      return (layer == 1 ? 72000 : 144000) * bitrate / samplingRate + padding;
+      return (layer == 1 ? 72 : 144) * bitrate / samplingRate + padding;
     }
   }
 
@@ -159,7 +169,7 @@ public final class MpegAudioHeader {
     if (layer == 3) {
       // Layer I (layer == 3)
       bitrate = version == 3 ? BITRATE_V1_L1[bitrateIndex - 1] : BITRATE_V2_L1[bitrateIndex - 1];
-      frameSize = (12000 * bitrate / sampleRate + padding) * 4;
+      frameSize = (12 * bitrate / sampleRate + padding) * 4;
       samplesPerFrame = 384;
     } else {
       // Layer II (layer == 2) or III (layer == 1)
@@ -167,19 +177,22 @@ public final class MpegAudioHeader {
         // Version 1
         bitrate = layer == 2 ? BITRATE_V1_L2[bitrateIndex - 1] : BITRATE_V1_L3[bitrateIndex - 1];
         samplesPerFrame = 1152;
-        frameSize = 144000 * bitrate / sampleRate + padding;
+        frameSize = 144 * bitrate / sampleRate + padding;
       } else {
         // Version 2 or 2.5.
         bitrate = BITRATE_V2[bitrateIndex - 1];
         samplesPerFrame = layer == 1 ? 576 : 1152;
-        frameSize = (layer == 1 ? 72000 : 144000) * bitrate / sampleRate + padding;
+        frameSize = (layer == 1 ? 72 : 144) * bitrate / sampleRate + padding;
       }
     }
 
+    // Calculate the bitrate in the same way Mp3Extractor calculates sample timestamps so that
+    // seeking to a given timestamp and playing from the start up to that timestamp give the same
+    // results for CBR streams. See also [internal: b/120390268].
+    bitrate = 8 * frameSize * sampleRate / samplesPerFrame;
     String mimeType = MIME_TYPE_BY_LAYER[3 - layer];
     int channels = ((headerData >> 6) & 3) == 3 ? 1 : 2;
-    header.setValues(version, mimeType, frameSize, sampleRate, channels, bitrate * 1000,
+    header.setValues(version, mimeType, frameSize, sampleRate, channels, bitrate, samplesPerFrame);
-        samplesPerFrame);
     return true;
   }
 
@@ -198,8 +211,14 @@ public final class MpegAudioHeader {
   /** Number of samples stored in the frame. */
   public int samplesPerFrame;
 
-  private void setValues(int version, String mimeType, int frameSize, int sampleRate, int channels,
+  private void setValues(
-      int bitrate, int samplesPerFrame) {
+      int version,
+      String mimeType,
+      int frameSize,
+      int sampleRate,
+      int channels,
+      int bitrate,
+      int samplesPerFrame) {
     this.version = version;
     this.mimeType = mimeType;
     this.frameSize = frameSize;

library/core/src/test/assets/mp3/play-trimmed.mp3.0.dump

@@ -1,6 +1,6 @@
 seekMap:
   isSeekable = true
-  duration = 26125
+  duration = 26122
   getPosition(0) = [[timeUs=0, position=0]]
 numberOfTracks = 1
 track 0:

library/core/src/test/assets/mp3/play-trimmed.mp3.1.dump

@@ -1,6 +1,6 @@
 seekMap:
   isSeekable = true
-  duration = 26125
+  duration = 26122
   getPosition(0) = [[timeUs=0, position=0]]
 numberOfTracks = 1
 track 0:

library/core/src/test/assets/mp3/play-trimmed.mp3.2.dump

@@ -1,6 +1,6 @@
 seekMap:
   isSeekable = true
-  duration = 26125
+  duration = 26122
   getPosition(0) = [[timeUs=0, position=0]]
 numberOfTracks = 1
 track 0:

library/core/src/test/assets/mp3/play-trimmed.mp3.3.dump

@@ -1,6 +1,6 @@
 seekMap:
   isSeekable = true
-  duration = 26125
+  duration = 26122
   getPosition(0) = [[timeUs=0, position=0]]
 numberOfTracks = 1
 track 0: