/*
* Copyright (C) 2019 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 androidx.media3.extractor;
import androidx.annotation.Nullable;
import androidx.media3.common.C;
import androidx.media3.common.DrmInitData;
import androidx.media3.common.Format;
import androidx.media3.common.MimeTypes;
import androidx.media3.common.util.ParsableBitArray;
import androidx.media3.common.util.ParsableByteArray;
import androidx.media3.common.util.UnstableApi;
import java.nio.ByteBuffer;
/** Utility methods for parsing AC-4 frames, which are access units in AC-4 bitstreams. */
@UnstableApi
public final class Ac4Util {
/** Holds sample format information as presented by a syncframe header. */
public static final class SyncFrameInfo {
/** The bitstream version. */
public final int bitstreamVersion;
/** The audio sampling rate in Hz. */
public final int sampleRate;
/** The number of audio channels */
public final int channelCount;
/** The size of the frame. */
public final int frameSize;
/** Number of audio samples in the frame. */
public final int sampleCount;
private SyncFrameInfo(
int bitstreamVersion, int channelCount, int sampleRate, int frameSize, int sampleCount) {
this.bitstreamVersion = bitstreamVersion;
this.channelCount = channelCount;
this.sampleRate = sampleRate;
this.frameSize = frameSize;
this.sampleCount = sampleCount;
}
}
public static final int AC40_SYNCWORD = 0xAC40;
public static final int AC41_SYNCWORD = 0xAC41;
/** Maximum rate for an AC-4 audio stream, in bytes per second. */
public static final int MAX_RATE_BYTES_PER_SECOND = 2688 * 1000 / 8;
/** The channel count of AC-4 stream. */
// TODO: Parse AC-4 stream channel count.
private static final int CHANNEL_COUNT_2 = 2;
/**
* The AC-4 sync frame header size for extractor. The seven bytes are 0xAC, 0x40, 0xFF, 0xFF,
* sizeByte1, sizeByte2, sizeByte3. See ETSI TS 103 190-1 V1.3.1, Annex G
*/
public static final int SAMPLE_HEADER_SIZE = 7;
/**
* The header size for AC-4 parser. Only needs to be as big as we need to read, not the full
* header size.
*/
public static final int HEADER_SIZE_FOR_PARSER = 16;
/**
* Number of audio samples in the frame. Defined in IEC61937-14:2017 table 5 and 6. This table
* provides the number of samples per frame at the playback sampling frequency of 48 kHz. For 44.1
* kHz, only frame_rate_index(13) is valid and corresponding sample count is 2048.
*/
private static final int[] SAMPLE_COUNT =
new int[] {
/* [ 0] 23.976 fps */ 2002,
/* [ 1] 24 fps */ 2000,
/* [ 2] 25 fps */ 1920,
/* [ 3] 29.97 fps */ 1601, // 1601 | 1602 | 1601 | 1602 | 1602
/* [ 4] 30 fps */ 1600,
/* [ 5] 47.95 fps */ 1001,
/* [ 6] 48 fps */ 1000,
/* [ 7] 50 fps */ 960,
/* [ 8] 59.94 fps */ 800, // 800 | 801 | 801 | 801 | 801
/* [ 9] 60 fps */ 800,
/* [10] 100 fps */ 480,
/* [11] 119.88 fps */ 400, // 400 | 400 | 401 | 400 | 401
/* [12] 120 fps */ 400,
/* [13] 23.438 fps */ 2048
};
/**
* Returns the AC-4 format given {@code data} containing the AC4SpecificBox according to ETSI TS
* 103 190-1 Annex E. The reading position of {@code data} will be modified.
*
* @param data The AC4SpecificBox to parse.
* @param trackId The track identifier to set on the format.
* @param language The language to set on the format.
* @param drmInitData {@link DrmInitData} to be included in the format.
* @return The AC-4 format parsed from data in the header.
*/
public static Format parseAc4AnnexEFormat(
ParsableByteArray data, String trackId, String language, @Nullable DrmInitData drmInitData) {
data.skipBytes(1); // ac4_dsi_version, bitstream_version[0:5]
int sampleRate = ((data.readUnsignedByte() & 0x20) >> 5 == 1) ? 48000 : 44100;
return new Format.Builder()
.setId(trackId)
.setSampleMimeType(MimeTypes.AUDIO_AC4)
.setChannelCount(CHANNEL_COUNT_2)
.setSampleRate(sampleRate)
.setDrmInitData(drmInitData)
.setLanguage(language)
.build();
}
/**
* Returns AC-4 format information given {@code data} containing a syncframe. The reading position
* of {@code data} will be modified.
*
* @param data The data to parse, positioned at the start of the syncframe.
* @return The AC-4 format data parsed from the header.
*/
public static SyncFrameInfo parseAc4SyncframeInfo(ParsableBitArray data) {
int headerSize = 0;
int syncWord = data.readBits(16);
headerSize += 2;
int frameSize = data.readBits(16);
headerSize += 2;
if (frameSize == 0xFFFF) {
frameSize = data.readBits(24);
headerSize += 3; // Extended frame_size
}
frameSize += headerSize;
if (syncWord == AC41_SYNCWORD) {
frameSize += 2; // crc_word
}
int bitstreamVersion = data.readBits(2);
if (bitstreamVersion == 3) {
bitstreamVersion += readVariableBits(data, /* bitsPerRead= */ 2);
}
int sequenceCounter = data.readBits(10);
if (data.readBit()) { // b_wait_frames
if (data.readBits(3) > 0) { // wait_frames
data.skipBits(2); // reserved
}
}
int sampleRate = data.readBit() ? 48000 : 44100;
int frameRateIndex = data.readBits(4);
int sampleCount = 0;
if (sampleRate == 44100 && frameRateIndex == 13) {
sampleCount = SAMPLE_COUNT[frameRateIndex];
} else if (sampleRate == 48000 && frameRateIndex < SAMPLE_COUNT.length) {
sampleCount = SAMPLE_COUNT[frameRateIndex];
switch (sequenceCounter % 5) {
case 1: // fall through
case 3:
if (frameRateIndex == 3 || frameRateIndex == 8) {
sampleCount++;
}
break;
case 2:
if (frameRateIndex == 8 || frameRateIndex == 11) {
sampleCount++;
}
break;
case 4:
if (frameRateIndex == 3 || frameRateIndex == 8 || frameRateIndex == 11) {
sampleCount++;
}
break;
default:
break;
}
}
return new SyncFrameInfo(bitstreamVersion, CHANNEL_COUNT_2, sampleRate, frameSize, sampleCount);
}
/**
* Returns the size in bytes of the given AC-4 syncframe.
*
* @param data The syncframe to parse.
* @param syncword The syncword value for the syncframe.
* @return The syncframe size in bytes, or {@link C#LENGTH_UNSET} if the input is invalid.
*/
public static int parseAc4SyncframeSize(byte[] data, int syncword) {
if (data.length < 7) {
return C.LENGTH_UNSET;
}
int headerSize = 2; // syncword
int frameSize = ((data[2] & 0xFF) << 8) | (data[3] & 0xFF);
headerSize += 2;
if (frameSize == 0xFFFF) {
frameSize = ((data[4] & 0xFF) << 16) | ((data[5] & 0xFF) << 8) | (data[6] & 0xFF);
headerSize += 3;
}
if (syncword == AC41_SYNCWORD) {
headerSize += 2;
}
frameSize += headerSize;
return frameSize;
}
/**
* Reads the number of audio samples represented by the given AC-4 syncframe. The buffer's
* position is not modified.
*
* @param buffer The {@link ByteBuffer} from which to read the syncframe.
* @return The number of audio samples represented by the syncframe.
*/
public static int parseAc4SyncframeAudioSampleCount(ByteBuffer buffer) {
byte[] bufferBytes = new byte[HEADER_SIZE_FOR_PARSER];
int position = buffer.position();
buffer.get(bufferBytes);
buffer.position(position);
return parseAc4SyncframeInfo(new ParsableBitArray(bufferBytes)).sampleCount;
}
/** Populates {@code buffer} with an AC-4 sample header for a sample of the specified size. */
public static void getAc4SampleHeader(int size, ParsableByteArray buffer) {
// See ETSI TS 103 190-1 V1.3.1, Annex G.
buffer.reset(SAMPLE_HEADER_SIZE);
byte[] data = buffer.getData();
data[0] = (byte) 0xAC;
data[1] = 0x40;
data[2] = (byte) 0xFF;
data[3] = (byte) 0xFF;
data[4] = (byte) ((size >> 16) & 0xFF);
data[5] = (byte) ((size >> 8) & 0xFF);
data[6] = (byte) (size & 0xFF);
}
private static int readVariableBits(ParsableBitArray data, int bitsPerRead) {
int value = 0;
while (true) {
value += data.readBits(bitsPerRead);
if (!data.readBit()) {
break;
}
value++;
value <<= bitsPerRead;
}
return value;
}
private Ac4Util() {}
}