Use the true bitrate for CBR MP3 seeking

PiperOrigin-RevId: 225989898

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 =
- {32, 64, 96, 128, 160, 192, 224, 256, 288, 320, 352, 384, 416, 448};
- private static final int[] BITRATE_V2_L1 =
- {32, 48, 56, 64, 80, 96, 112, 128, 144, 160, 176, 192, 224, 256};
- private static final int[] BITRATE_V1_L2 =
- {32, 48, 56, 64, 80, 96, 112, 128, 160, 192, 224, 256, 320, 384};
- private static final int[] BITRATE_V1_L3 =
- {32, 40, 48, 56, 64, 80, 96, 112, 128, 160, 192, 224, 256, 320};
- private static final int[] BITRATE_V2 =
- {8, 16, 24, 32, 40, 48, 56, 64, 80, 96, 112, 128, 144, 160};
+ private static final int[] BITRATE_V1_L1 = {
+ 32000, 64000, 96000, 128000, 160000, 192000, 224000, 256000, 288000, 320000, 352000, 384000,
+ 416000, 448000
+ };
+ private static final int[] BITRATE_V2_L1 = {
+ 32000, 48000, 56000, 64000, 80000, 96000, 112000, 128000, 144000, 160000, 176000, 192000,
+ 224000, 256000
+ };
+ private static final int[] BITRATE_V1_L2 = {
+ 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 static int getFrameSize(int header) {
  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 static int getFrameSize(int header) {
 
  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;
  }
  }
 
@@ -159,27 +169,30 @@ public static boolean populateHeader(int headerData, MpegAudioHeader header) {
  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)
  if (version == 3) {
  // 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,
- samplesPerFrame);
+ header.setValues(version, mimeType, frameSize, sampleRate, channels, bitrate, samplesPerFrame);
  return true;
  }
 
@@ -198,8 +211,14 @@ public static boolean populateHeader(int headerData, MpegAudioHeader header) {
  /** Number of samples stored in the frame. */
  public int samplesPerFrame;
 
- private void setValues(int version, String mimeType, int frameSize, int sampleRate, int channels,
- int bitrate, int samplesPerFrame) {
+ private void setValues(
+ 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: