[191] | 1 | /* The copyright in this software is being made available under the BSD |
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| 2 | * License, included below. This software may be subject to other third party |
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| 3 | * and contributor rights, including patent rights, and no such rights are |
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| 4 | * granted under this license. |
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| 5 | * |
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| 6 | * Copyright (c) 2010-2013, ITU/ISO/IEC |
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| 7 | * All rights reserved. |
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| 8 | * |
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| 9 | * Redistribution and use in source and binary forms, with or without |
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| 10 | * modification, are permitted provided that the following conditions are met: |
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| 11 | * |
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| 12 | * * Redistributions of source code must retain the above copyright notice, |
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| 13 | * this list of conditions and the following disclaimer. |
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| 14 | * * Redistributions in binary form must reproduce the above copyright notice, |
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| 15 | * this list of conditions and the following disclaimer in the documentation |
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| 16 | * and/or other materials provided with the distribution. |
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| 17 | * * Neither the name of the ITU/ISO/IEC nor the names of its contributors may |
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| 18 | * be used to endorse or promote products derived from this software without |
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| 19 | * specific prior written permission. |
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| 20 | * |
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| 21 | * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" |
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| 22 | * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE |
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| 23 | * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE |
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| 24 | * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS |
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| 25 | * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR |
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| 26 | * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF |
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| 27 | * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS |
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| 28 | * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN |
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| 29 | * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) |
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| 30 | * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF |
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| 31 | * THE POSSIBILITY OF SUCH DAMAGE. |
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| 32 | */ |
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| 33 | |
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| 34 | /** |
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| 35 | \file AnnexBread.cpp |
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| 36 | \brief reading functions for Annex B byte streams |
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| 37 | */ |
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| 38 | |
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| 39 | |
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| 40 | #include <stdint.h> |
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| 41 | #include <cassert> |
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| 42 | #include <vector> |
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| 43 | #include "AnnexBread.h" |
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| 44 | |
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| 45 | using namespace std; |
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| 46 | |
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| 47 | //! \ingroup TLibDecoder |
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| 48 | //! \{ |
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| 49 | |
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| 50 | /** |
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| 51 | * Parse an AVC AnnexB Bytestream bs to extract a single nalUnit |
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| 52 | * while accumulating bytestream statistics into stats. |
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| 53 | * |
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| 54 | * If EOF occurs while trying to extract a NALunit, an exception |
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| 55 | * of std::ios_base::failure is thrown. The contsnts of stats will |
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| 56 | * be correct at this point. |
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| 57 | */ |
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| 58 | static void |
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| 59 | _byteStreamNALUnit( |
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| 60 | InputByteStream& bs, |
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| 61 | vector<uint8_t>& nalUnit, |
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| 62 | AnnexBStats& stats) |
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| 63 | { |
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| 64 | /* At the beginning of the decoding process, the decoder initialises its |
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| 65 | * current position in the byte stream to the beginning of the byte stream. |
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| 66 | * It then extracts and discards each leading_zero_8bits syntax element (if |
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| 67 | * present), moving the current position in the byte stream forward one |
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| 68 | * byte at a time, until the current position in the byte stream is such |
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| 69 | * that the next four bytes in the bitstream form the four-byte sequence |
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| 70 | * 0x00000001. |
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| 71 | */ |
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| 72 | while ((bs.eofBeforeNBytes(24/8) || bs.peekBytes(24/8) != 0x000001) |
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| 73 | && (bs.eofBeforeNBytes(32/8) || bs.peekBytes(32/8) != 0x00000001)) |
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| 74 | { |
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| 75 | uint8_t leading_zero_8bits = bs.readByte(); |
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| 76 | assert(leading_zero_8bits == 0); |
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| 77 | stats.m_numLeadingZero8BitsBytes++; |
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| 78 | } |
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| 79 | |
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| 80 | /* 1. When the next four bytes in the bitstream form the four-byte sequence |
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| 81 | * 0x00000001, the next byte in the byte stream (which is a zero_byte |
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| 82 | * syntax element) is extracted and discarded and the current position in |
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| 83 | * the byte stream is set equal to the position of the byte following this |
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| 84 | * discarded byte. |
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| 85 | */ |
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| 86 | /* NB, the previous step guarantees this will succeed -- if EOF was |
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| 87 | * encountered, an exception will stop execution getting this far */ |
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| 88 | if (bs.peekBytes(24/8) != 0x000001) |
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| 89 | { |
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| 90 | uint8_t zero_byte = bs.readByte(); |
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| 91 | assert(zero_byte == 0); |
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| 92 | stats.m_numZeroByteBytes++; |
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| 93 | } |
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| 94 | |
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| 95 | /* 2. The next three-byte sequence in the byte stream (which is a |
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| 96 | * start_code_prefix_one_3bytes) is extracted and discarded and the current |
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| 97 | * position in the byte stream is set equal to the position of the byte |
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| 98 | * following this three-byte sequence. |
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| 99 | */ |
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| 100 | /* NB, (1) guarantees that the next three bytes are 0x00 00 01 */ |
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| 101 | uint32_t start_code_prefix_one_3bytes = bs.readBytes(24/8); |
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| 102 | assert(start_code_prefix_one_3bytes == 0x000001); |
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| 103 | stats.m_numStartCodePrefixBytes += 3; |
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| 104 | |
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| 105 | /* 3. NumBytesInNALunit is set equal to the number of bytes starting with |
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| 106 | * the byte at the current position in the byte stream up to and including |
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| 107 | * the last byte that precedes the location of any of the following |
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| 108 | * conditions: |
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| 109 | * a. A subsequent byte-aligned three-byte sequence equal to 0x000000, or |
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| 110 | * b. A subsequent byte-aligned three-byte sequence equal to 0x000001, or |
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| 111 | * c. The end of the byte stream, as determined by unspecified means. |
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| 112 | */ |
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| 113 | /* 4. NumBytesInNALunit bytes are removed from the bitstream and the |
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| 114 | * current position in the byte stream is advanced by NumBytesInNALunit |
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| 115 | * bytes. This sequence of bytes is nal_unit( NumBytesInNALunit ) and is |
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| 116 | * decoded using the NAL unit decoding process |
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| 117 | */ |
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| 118 | /* NB, (unsigned)x > 2 implies n!=0 && n!=1 */ |
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| 119 | while (bs.eofBeforeNBytes(24/8) || bs.peekBytes(24/8) > 2) |
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| 120 | { |
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| 121 | nalUnit.push_back(bs.readByte()); |
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| 122 | } |
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| 123 | |
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| 124 | /* 5. When the current position in the byte stream is: |
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| 125 | * - not at the end of the byte stream (as determined by unspecified means) |
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| 126 | * - and the next bytes in the byte stream do not start with a three-byte |
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| 127 | * sequence equal to 0x000001 |
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| 128 | * - and the next bytes in the byte stream do not start with a four byte |
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| 129 | * sequence equal to 0x00000001, |
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| 130 | * the decoder extracts and discards each trailing_zero_8bits syntax |
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| 131 | * element, moving the current position in the byte stream forward one byte |
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| 132 | * at a time, until the current position in the byte stream is such that: |
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| 133 | * - the next bytes in the byte stream form the four-byte sequence |
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| 134 | * 0x00000001 or |
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| 135 | * - the end of the byte stream has been encountered (as determined by |
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| 136 | * unspecified means). |
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| 137 | */ |
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| 138 | /* NB, (3) guarantees there are at least three bytes available or none */ |
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| 139 | while ((bs.eofBeforeNBytes(24/8) || bs.peekBytes(24/8) != 0x000001) |
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| 140 | && (bs.eofBeforeNBytes(32/8) || bs.peekBytes(32/8) != 0x00000001)) |
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| 141 | { |
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| 142 | uint8_t trailing_zero_8bits = bs.readByte(); |
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| 143 | assert(trailing_zero_8bits == 0); |
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| 144 | stats.m_numTrailingZero8BitsBytes++; |
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| 145 | } |
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| 146 | } |
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| 147 | |
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| 148 | /** |
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| 149 | * Parse an AVC AnnexB Bytestream bs to extract a single nalUnit |
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| 150 | * while accumulating bytestream statistics into stats. |
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| 151 | * |
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| 152 | * Returns false if EOF was reached (NB, nalunit data may be valid), |
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| 153 | * otherwise true. |
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| 154 | */ |
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| 155 | Bool |
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| 156 | byteStreamNALUnit( |
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| 157 | InputByteStream& bs, |
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| 158 | vector<uint8_t>& nalUnit, |
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| 159 | AnnexBStats& stats) |
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| 160 | { |
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| 161 | Bool eof = false; |
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| 162 | try |
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| 163 | { |
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| 164 | _byteStreamNALUnit(bs, nalUnit, stats); |
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| 165 | } |
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| 166 | catch (...) |
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| 167 | { |
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| 168 | eof = true; |
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| 169 | } |
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| 170 | stats.m_numBytesInNALUnit = UInt(nalUnit.size()); |
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| 171 | return eof; |
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| 172 | } |
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| 173 | //! \} |
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