1 // Copyright 2014 The Chromium Authors. All rights reserved.
2 // Use of this source code is governed by a BSD-style license that can be
3 // found in the LICENSE file.
4
5 #include "media/formats/mp2t/ts_section_psi.h"
6
7 #include "base/basictypes.h"
8 #include "base/logging.h"
9 #include "media/base/bit_reader.h"
10 #include "media/formats/mp2t/mp2t_common.h"
11
IsCrcValid(const uint8 * buf,int size)12 static bool IsCrcValid(const uint8* buf, int size) {
13 uint32 crc = 0xffffffffu;
14 const uint32 kCrcPoly = 0x4c11db7;
15
16 for (int k = 0; k < size; k++) {
17 int nbits = 8;
18 uint32 data_msb_aligned = buf[k];
19 data_msb_aligned <<= (32 - nbits);
20
21 while (nbits > 0) {
22 if ((data_msb_aligned ^ crc) & 0x80000000) {
23 crc <<= 1;
24 crc ^= kCrcPoly;
25 } else {
26 crc <<= 1;
27 }
28
29 data_msb_aligned <<= 1;
30 nbits--;
31 }
32 }
33
34 return (crc == 0);
35 }
36
37 namespace media {
38 namespace mp2t {
39
TsSectionPsi()40 TsSectionPsi::TsSectionPsi()
41 : wait_for_pusi_(true),
42 leading_bytes_to_discard_(0) {
43 }
44
~TsSectionPsi()45 TsSectionPsi::~TsSectionPsi() {
46 }
47
Parse(bool payload_unit_start_indicator,const uint8 * buf,int size)48 bool TsSectionPsi::Parse(bool payload_unit_start_indicator,
49 const uint8* buf, int size) {
50 // Ignore partial PSI.
51 if (wait_for_pusi_ && !payload_unit_start_indicator)
52 return true;
53
54 if (payload_unit_start_indicator) {
55 // Reset the state of the PSI section.
56 ResetPsiState();
57
58 // Update the state.
59 wait_for_pusi_ = false;
60 DCHECK_GE(size, 1);
61 int pointer_field = buf[0];
62 leading_bytes_to_discard_ = pointer_field;
63 buf++;
64 size--;
65 }
66
67 // Discard some leading bytes if needed.
68 if (leading_bytes_to_discard_ > 0) {
69 int nbytes_to_discard = std::min(leading_bytes_to_discard_, size);
70 buf += nbytes_to_discard;
71 size -= nbytes_to_discard;
72 leading_bytes_to_discard_ -= nbytes_to_discard;
73 }
74 if (size == 0)
75 return true;
76
77 // Add the data to the parser state.
78 psi_byte_queue_.Push(buf, size);
79 int raw_psi_size;
80 const uint8* raw_psi;
81 psi_byte_queue_.Peek(&raw_psi, &raw_psi_size);
82
83 // Check whether we have enough data to start parsing.
84 if (raw_psi_size < 3)
85 return true;
86 int section_length =
87 ((static_cast<int>(raw_psi[1]) << 8) |
88 (static_cast<int>(raw_psi[2]))) & 0xfff;
89 if (section_length >= 1021)
90 return false;
91 int psi_length = section_length + 3;
92 if (raw_psi_size < psi_length) {
93 // Don't throw an error when there is not enough data,
94 // just wait for more data to come.
95 return true;
96 }
97
98 // There should not be any trailing bytes after a PMT.
99 // Instead, the pointer field should be used to stuff bytes.
100 DVLOG_IF(1, raw_psi_size > psi_length)
101 << "Trailing bytes after a PSI section: "
102 << psi_length << " vs " << raw_psi_size;
103
104 // Verify the CRC.
105 RCHECK(IsCrcValid(raw_psi, psi_length));
106
107 // Parse the PSI section.
108 BitReader bit_reader(raw_psi, raw_psi_size);
109 bool status = ParsePsiSection(&bit_reader);
110 if (status)
111 ResetPsiState();
112
113 return status;
114 }
115
Flush()116 void TsSectionPsi::Flush() {
117 }
118
Reset()119 void TsSectionPsi::Reset() {
120 ResetPsiSection();
121 ResetPsiState();
122 }
123
ResetPsiState()124 void TsSectionPsi::ResetPsiState() {
125 wait_for_pusi_ = true;
126 psi_byte_queue_.Reset();
127 leading_bytes_to_discard_ = 0;
128 }
129
130 } // namespace mp2t
131 } // namespace media
132
133