/*
* Copyright (C) 2014 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.exoplayer.util;
import java.util.Arrays;
/**
* Utility methods for handling H.264/AVC and H.265/HEVC NAL units.
*/
public final class NalUnitUtil {
/** Four initial bytes that must prefix NAL units for decoding. */
public static final byte[] NAL_START_CODE = new byte[] {0, 0, 0, 1};
/** Value for aspect_ratio_idc indicating an extended aspect ratio, in H.264 and H.265 SPSs. */
public static final int EXTENDED_SAR = 0xFF;
/** Aspect ratios indexed by aspect_ratio_idc, in H.264 and H.265 SPSs. */
public static final float[] ASPECT_RATIO_IDC_VALUES = new float[] {
1f /* Unspecified. Assume square */,
1f,
12f / 11f,
10f / 11f,
16f / 11f,
40f / 33f,
24f / 11f,
20f / 11f,
32f / 11f,
80f / 33f,
18f / 11f,
15f / 11f,
64f / 33f,
160f / 99f,
4f / 3f,
3f / 2f,
2f
};
private static final Object scratchEscapePositionsLock = new Object();
/**
* Temporary store for positions of escape codes in {@link #unescapeStream(byte[], int)}. Guarded
* by {@link #scratchEscapePositionsLock}.
*/
private static int[] scratchEscapePositions = new int[10];
/**
* Unescapes {@code data} up to the specified limit, replacing occurrences of [0, 0, 3] with
* [0, 0]. The unescaped data is returned in-place, with the return value indicating its length.
* <p>
* Executions of this method are mutually exclusive, so it should not be called with very large
* buffers.
*
* @param data The data to unescape.
* @param limit The limit (exclusive) of the data to unescape.
* @return The length of the unescaped data.
*/
public static int unescapeStream(byte[] data, int limit) {
synchronized (scratchEscapePositionsLock) {
int position = 0;
int scratchEscapeCount = 0;
while (position < limit) {
position = findNextUnescapeIndex(data, position, limit);
if (position < limit) {
if (scratchEscapePositions.length <= scratchEscapeCount) {
// Grow scratchEscapePositions to hold a larger number of positions.
scratchEscapePositions = Arrays.copyOf(scratchEscapePositions,
scratchEscapePositions.length * 2);
}
scratchEscapePositions[scratchEscapeCount++] = position;
position += 3;
}
}
int unescapedLength = limit - scratchEscapeCount;
int escapedPosition = 0; // The position being read from.
int unescapedPosition = 0; // The position being written to.
for (int i = 0; i < scratchEscapeCount; i++) {
int nextEscapePosition = scratchEscapePositions[i];
int copyLength = nextEscapePosition - escapedPosition;
System.arraycopy(data, escapedPosition, data, unescapedPosition, copyLength);
unescapedPosition += copyLength;
data[unescapedPosition++] = 0;
data[unescapedPosition++] = 0;
escapedPosition += copyLength + 3;
}
int remainingLength = unescapedLength - unescapedPosition;
System.arraycopy(data, escapedPosition, data, unescapedPosition, remainingLength);
return unescapedLength;
}
}
/**
* Constructs and returns a NAL unit with a start code followed by the data in {@code atom}.
*/
public static byte[] parseChildNalUnit(ParsableByteArray atom) {
int length = atom.readUnsignedShort();
int offset = atom.getPosition();
atom.skipBytes(length);
return CodecSpecificDataUtil.buildNalUnit(atom.data, offset, length);
}
/**
* Gets the type of the NAL unit in {@code data} that starts at {@code offset}.
*
* @param data The data to search.
* @param offset The start offset of a NAL unit. Must lie between {@code -3} (inclusive) and
* {@code data.length - 3} (exclusive).
* @return The type of the unit.
*/
public static int getNalUnitType(byte[] data, int offset) {
return data[offset + 3] & 0x1F;
}
/**
* Gets the type of the H.265 NAL unit in {@code data} that starts at {@code offset}.
*
* @param data The data to search.
* @param offset The start offset of a NAL unit. Must lie between {@code -3} (inclusive) and
* {@code data.length - 3} (exclusive).
* @return The type of the unit.
*/
public static int getH265NalUnitType(byte[] data, int offset) {
return (data[offset + 3] & 0x7E) >> 1;
}
/**
* Finds the first NAL unit in {@code data}.
* <p>
* If {@code prefixFlags} is null then the first three bytes of a NAL unit must be entirely
* contained within the part of the array being searched in order for it to be found.
* <p>
* When {@code prefixFlags} is non-null, this method supports finding NAL units whose first four
* bytes span {@code data} arrays passed to successive calls. To use this feature, pass the same
* {@code prefixFlags} parameter to successive calls. State maintained in this parameter enables
* the detection of such NAL units. Note that when using this feature, the return value may be 3,
* 2 or 1 less than {@code startOffset}, to indicate a NAL unit starting 3, 2 or 1 bytes before
* the first byte in the current array.
*
* @param data The data to search.
* @param startOffset The offset (inclusive) in the data to start the search.
* @param endOffset The offset (exclusive) in the data to end the search.
* @param prefixFlags A boolean array whose first three elements are used to store the state
* required to detect NAL units where the NAL unit prefix spans array boundaries. The array
* must be at least 3 elements long.
* @return The offset of the NAL unit, or {@code endOffset} if a NAL unit was not found.
*/
public static int findNalUnit(byte[] data, int startOffset, int endOffset,
boolean[] prefixFlags) {
int length = endOffset - startOffset;
Assertions.checkState(length >= 0);
if (length == 0) {
return endOffset;
}
if (prefixFlags != null) {
if (prefixFlags[0]) {
clearPrefixFlags(prefixFlags);
return startOffset - 3;
} else if (length > 1 && prefixFlags[1] && data[startOffset] == 1) {
clearPrefixFlags(prefixFlags);
return startOffset - 2;
} else if (length > 2 && prefixFlags[2] && data[startOffset] == 0
&& data[startOffset + 1] == 1) {
clearPrefixFlags(prefixFlags);
return startOffset - 1;
}
}
int limit = endOffset - 1;
// We're looking for the NAL unit start code prefix 0x000001. The value of i tracks the index of
// the third byte.
for (int i = startOffset + 2; i < limit; i += 3) {
if ((data[i] & 0xFE) != 0) {
// There isn't a NAL prefix here, or at the next two positions. Do nothing and let the
// loop advance the index by three.
} else if (data[i - 2] == 0 && data[i - 1] == 0 && data[i] == 1) {
if (prefixFlags != null) {
clearPrefixFlags(prefixFlags);
}
return i - 2;
} else {
// There isn't a NAL prefix here, but there might be at the next position. We should
// only skip forward by one. The loop will skip forward by three, so subtract two here.
i -= 2;
}
}
if (prefixFlags != null) {
// True if the last three bytes in the data seen so far are {0,0,1}.
prefixFlags[0] = length > 2
? (data[endOffset - 3] == 0 && data[endOffset - 2] == 0 && data[endOffset - 1] == 1)
: length == 2 ? (prefixFlags[2] && data[endOffset - 2] == 0 && data[endOffset - 1] == 1)
: (prefixFlags[1] && data[endOffset - 1] == 1);
// True if the last two bytes in the data seen so far are {0,0}.
prefixFlags[1] = length > 1 ? data[endOffset - 2] == 0 && data[endOffset - 1] == 0
: prefixFlags[2] && data[endOffset - 1] == 0;
// True if the last byte in the data seen so far is {0}.
prefixFlags[2] = data[endOffset - 1] == 0;
}
return endOffset;
}
/**
* Clears prefix flags, as used by {@link #findNalUnit(byte[], int, int, boolean[])}.
*
* @param prefixFlags The flags to clear.
*/
public static void clearPrefixFlags(boolean[] prefixFlags) {
prefixFlags[0] = false;
prefixFlags[1] = false;
prefixFlags[2] = false;
}
private static int findNextUnescapeIndex(byte[] bytes, int offset, int limit) {
for (int i = offset; i < limit - 2; i++) {
if (bytes[i] == 0x00 && bytes[i + 1] == 0x00 && bytes[i + 2] == 0x03) {
return i;
}
}
return limit;
}
private NalUnitUtil() {
// Prevent instantiation.
}
}