DrKLO/Telegram · error · OpusDecoderException

Invalid pre-skip or seek pre-roll

Error message

Invalid pre-skip or seek pre-roll

What it means

When initializationData has 3 elements, the constructor insists that elements at index 1 (codec delay) and index 2 (seek pre-roll) are each exactly 8 bytes long, since they are read as native-order longs holding nanosecond values (see getPreSkipSamples/getSeekPreRollSamples). If either buffer is not 8 bytes the decoder rejects the data as malformed pre-skip/pre-roll.

Source

Thrown at TMessagesProj/src/main/java/com/google/android/exoplayer2/ext/opus/OpusDecoder.java:97

      List<byte[]> initializationData,
      @Nullable CryptoConfig cryptoConfig,
      boolean outputFloat)
      throws OpusDecoderException {
    super(new DecoderInputBuffer[numInputBuffers], new SimpleDecoderOutputBuffer[numOutputBuffers]);
    if (!OpusLibrary.isAvailable()) {
      throw new OpusDecoderException("Failed to load decoder native libraries");
    }
    this.cryptoConfig = cryptoConfig;
    if (cryptoConfig != null && !OpusLibrary.opusIsSecureDecodeSupported()) {
      throw new OpusDecoderException("Opus decoder does not support secure decode");
    }
    int initializationDataSize = initializationData.size();
    if (initializationDataSize != 1 && initializationDataSize != 3) {
      throw new OpusDecoderException("Invalid initialization data size");
    }
    if (initializationDataSize == 3
        && (initializationData.get(1).length != 8 || initializationData.get(2).length != 8)) {
      throw new OpusDecoderException("Invalid pre-skip or seek pre-roll");
    }
    preSkipSamples = getPreSkipSamples(initializationData);
    seekPreRollSamples = getSeekPreRollSamples(initializationData);
    skipSamples = preSkipSamples;

    byte[] headerBytes = initializationData.get(0);
    if (headerBytes.length < 19) {
      throw new OpusDecoderException("Invalid header length");
    }
    channelCount = getChannelCount(headerBytes);
    if (channelCount > 8) {
      throw new OpusDecoderException("Invalid channel count: " + channelCount);
    }
    int gain = readSignedLittleEndian16(headerBytes, 16);

    byte[] streamMap = new byte[8];
    int numStreams;
    int numCoupled;

View on GitHub (pinned to 45ab8f4308)

Solutions

1. Emit codec delay and seek pre-roll as 8-byte native-order longs (nanoseconds) in initializationData[1] and [2].
2. If you only have a header, pass a single-element list (initializationData.size() == 1) so the decoder falls back to parsing pre-skip from the header and the default 3840-sample pre-roll.

Example fix

// before - wrong: 4-byte buffers
init.add(intToBytes(codecDelayNs));
init.add(intToBytes(seekPreRollNs));

// after
ByteBuffer b = ByteBuffer.allocate(8).order(ByteOrder.nativeOrder());
b.putLong(codecDelayNs); init.add(b.array());
ByteBuffer p = ByteBuffer.allocate(8).order(ByteOrder.nativeOrder());
p.putLong(seekPreRollNs); init.add(p.array());

List<byte[]> init = format.initializationData;
if (init.size() == 3 && (init.get(1).length != 8 || init.get(2).length != 8)) {
  throw new IllegalArgumentException(
      "Opus codec-delay/seek-pre-roll buffers must each be 8 bytes");
}
new OpusDecoder(NUM_BUFFERS, NUM_BUFFERS, initSize, init, cryptoConfig, outputFloat);

try {
  new OpusDecoder(..., format.initializationData, cryptoConfig, outputFloat);
} catch (OpusDecoderException e) {
  if (e.getMessage().contains("pre-skip or seek pre-roll")) {
    // rebuild init with two 8-byte native longs, or use a single-element list
  } else { throw e; }
}

When it happens

Trigger: A 3-element initializationData list whose trailing buffers are the wrong length - e.g. a custom muxer wrote codec delay as a 4-byte int, or the extractor emitted a truncated buffer.

Common situations: Home-grown Opus muxers/demuxers that do not follow ExoPlayer's 8-byte-long convention for codec delay and seek pre-roll; test fixtures with placeholder byte arrays of the wrong size.

Related errors

• Invalid initialization data size
• Invalid header length
• Invalid channel count: {channelCount}
• Invalid header, missing stream map
• Opus decoder does not support secure decode

AI-assisted analysis of DrKLO/Telegram@45ab8f4308 (2026-08-14). Data as JSON: /api/errors/a545d63270607daf. Report an issue: GitHub.