android-34/com/google/android/exoplayer2/extractor/CeaUtil.java

/*
 * Copyright (C) 2017 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package com.google.android.exoplayer2.extractor;

import com.google.android.exoplayer2.C;
import com.google.android.exoplayer2.util.Log;
import com.google.android.exoplayer2.util.ParsableByteArray;

/** Utility methods for handling CEA-608/708 messages. Defined in A/53 Part 4:2009. */
public final class CeaUtil {

  private static final String TAG = "CeaUtil";

  public static final int USER_DATA_IDENTIFIER_GA94 = 0x47413934;
  public static final int USER_DATA_TYPE_CODE_MPEG_CC = 0x3;

  private static final int PAYLOAD_TYPE_CC = 4;
  private static final int COUNTRY_CODE = 0xB5;
  private static final int PROVIDER_CODE_ATSC = 0x31;
  private static final int PROVIDER_CODE_DIRECTV = 0x2F;

  /**
   * Consumes the unescaped content of an SEI NAL unit, writing the content of any CEA-608/708
   * messages as samples to all of the provided outputs.
   *
   * @param presentationTimeUs The presentation time in microseconds for any samples.
   * @param seiBuffer The unescaped SEI NAL unit data, excluding the NAL unit start code and type.
   * @param outputs The outputs to which any samples should be written.
   */
  public static void consume(
      long presentationTimeUs, ParsableByteArray seiBuffer, TrackOutput[] outputs) {
    while (seiBuffer.bytesLeft() > 1 /* last byte will be rbsp_trailing_bits */) {
      int payloadType = readNon255TerminatedValue(seiBuffer);
      int payloadSize = readNon255TerminatedValue(seiBuffer);
      int nextPayloadPosition = seiBuffer.getPosition() + payloadSize;
      // Process the payload.
      if (payloadSize == -1 || payloadSize > seiBuffer.bytesLeft()) {
        // This might occur if we're trying to read an encrypted SEI NAL unit.
        Log.w(TAG, "Skipping remainder of malformed SEI NAL unit.");
        nextPayloadPosition = seiBuffer.limit();
      } else if (payloadType == PAYLOAD_TYPE_CC && payloadSize >= 8) {
        int countryCode = seiBuffer.readUnsignedByte();
        int providerCode = seiBuffer.readUnsignedShort();
        int userIdentifier = 0;
        if (providerCode == PROVIDER_CODE_ATSC) {
          userIdentifier = seiBuffer.readInt();
        }
        int userDataTypeCode = seiBuffer.readUnsignedByte();
        if (providerCode == PROVIDER_CODE_DIRECTV) {
          seiBuffer.skipBytes(1); // user_data_length.
        }
        boolean messageIsSupportedCeaCaption =
            countryCode == COUNTRY_CODE
                && (providerCode == PROVIDER_CODE_ATSC || providerCode == PROVIDER_CODE_DIRECTV)
                && userDataTypeCode == USER_DATA_TYPE_CODE_MPEG_CC;
        if (providerCode == PROVIDER_CODE_ATSC) {
          messageIsSupportedCeaCaption &= userIdentifier == USER_DATA_IDENTIFIER_GA94;
        }
        if (messageIsSupportedCeaCaption) {
          consumeCcData(presentationTimeUs, seiBuffer, outputs);
        }
      }
      seiBuffer.setPosition(nextPayloadPosition);
    }
  }

  /**
   * Consumes caption data (cc_data), writing the content as samples to all of the provided outputs.
   *
   * @param presentationTimeUs The presentation time in microseconds for any samples.
   * @param ccDataBuffer The buffer containing the caption data.
   * @param outputs The outputs to which any samples should be written.
   */
  public static void consumeCcData(
      long presentationTimeUs, ParsableByteArray ccDataBuffer, TrackOutput[] outputs) {
    // First byte contains: reserved (1), process_cc_data_flag (1), zero_bit (1), cc_count (5).
    int firstByte = ccDataBuffer.readUnsignedByte();
    boolean processCcDataFlag = (firstByte & 0x40) != 0;
    if (!processCcDataFlag) {
      // No need to process.
      return;
    }
    int ccCount = firstByte & 0x1F;
    ccDataBuffer.skipBytes(1); // Ignore em_data
    // Each data packet consists of 24 bits: marker bits (5) + cc_valid (1) + cc_type (2)
    // + cc_data_1 (8) + cc_data_2 (8).
    int sampleLength = ccCount * 3;
    int sampleStartPosition = ccDataBuffer.getPosition();
    for (TrackOutput output : outputs) {
      ccDataBuffer.setPosition(sampleStartPosition);
      output.sampleData(ccDataBuffer, sampleLength);
      if (presentationTimeUs != C.TIME_UNSET) {
        output.sampleMetadata(
            presentationTimeUs,
            C.BUFFER_FLAG_KEY_FRAME,
            sampleLength,
            /* offset= */ 0,
            /* cryptoData= */ null);
      }
    }
  }

  /**
   * Reads a value from the provided buffer consisting of zero or more 0xFF bytes followed by a
   * terminating byte not equal to 0xFF. The returned value is ((0xFF * N) + T), where N is the
   * number of 0xFF bytes and T is the value of the terminating byte.
   *
   * @param buffer The buffer from which to read the value.
   * @return The read value, or -1 if the end of the buffer is reached before a value is read.
   */
  private static int readNon255TerminatedValue(ParsableByteArray buffer) {
    int b;
    int value = 0;
    do {
      if (buffer.bytesLeft() == 0) {
        return -1;
      }
      b = buffer.readUnsignedByte();
      value += b;
    } while (b == 0xFF);
    return value;
  }

  private CeaUtil() {}
}