media/formats/mp2t/ts_section_pes.cc

   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_pes.h"
   6
   7 #include "base/logging.h"
   8 #include "base/strings/string_number_conversions.h"
   9 #include "media/base/bit_reader.h"
  10 #include "media/base/buffers.h"
  11 #include "media/formats/mp2t/es_parser.h"
  12 #include "media/formats/mp2t/mp2t_common.h"
  13
  14 static const int kPesStartCode = 0x000001;
  15
  16 // Given that |time| is coded using 33 bits,
  17 // UnrollTimestamp returns the corresponding unrolled timestamp.
  18 // The unrolled timestamp is defined by:
  19 // |time| + k * (2 ^ 33)
  20 // where k is estimated so that the unrolled timestamp
  21 // is as close as possible to |previous_unrolled_time|.
  22 static int64 UnrollTimestamp(int64 previous_unrolled_time, int64 time) {
  23   // Mpeg2 TS timestamps have an accuracy of 33 bits.
  24   const int nbits = 33;
  25
  26   // |timestamp| has a precision of |nbits|
  27   // so make sure the highest bits are set to 0.
  28   DCHECK_EQ((time >> nbits), 0);
  29
  30   // Consider 3 possibilities to estimate the missing high bits of |time|.
  31   int64 previous_unrolled_time_high =
  32       (previous_unrolled_time >> nbits);
  33   int64 time0 = ((previous_unrolled_time_high - 1) << nbits) | time;
  34   int64 time1 = ((previous_unrolled_time_high + 0) << nbits) | time;
  35   int64 time2 = ((previous_unrolled_time_high + 1) << nbits) | time;
  36
  37   // Select the min absolute difference with the current time
  38   // so as to ensure time continuity.
  39   int64 diff0 = time0 - previous_unrolled_time;
  40   int64 diff1 = time1 - previous_unrolled_time;
  41   int64 diff2 = time2 - previous_unrolled_time;
  42   if (diff0 < 0)
  43     diff0 = -diff0;
  44   if (diff1 < 0)
  45     diff1 = -diff1;
  46   if (diff2 < 0)
  47     diff2 = -diff2;
  48
  49   int64 unrolled_time;
  50   int64 min_diff;
  51   if (diff1 < diff0) {
  52     unrolled_time = time1;
  53     min_diff = diff1;
  54   } else {
  55     unrolled_time = time0;
  56     min_diff = diff0;
  57   }
  58   if (diff2 < min_diff)
  59     unrolled_time = time2;
  60
  61   return unrolled_time;
  62 }
  63
  64 static bool IsTimestampSectionValid(int64 timestamp_section) {
  65   // |pts_section| has 40 bits:
  66   // - starting with either '0010' or '0011' or '0001'
  67   // - and ending with a marker bit.
  68   // See ITU H.222 standard - PES section.
  69
  70   // Verify that all the marker bits are set to one.
  71   return ((timestamp_section & 0x1) != 0) &&
  72          ((timestamp_section & 0x10000) != 0) &&
  73          ((timestamp_section & 0x100000000) != 0);
  74 }
  75
  76 static int64 ConvertTimestampSectionToTimestamp(int64 timestamp_section) {
  77   return (((timestamp_section >> 33) & 0x7) << 30) |
  78          (((timestamp_section >> 17) & 0x7fff) << 15) |
  79          (((timestamp_section >> 1) & 0x7fff) << 0);
  80 }
  81
  82 namespace media {
  83 namespace mp2t {
  84
  85 TsSectionPes::TsSectionPes(scoped_ptr<EsParser> es_parser)
  86   : es_parser_(es_parser.release()),
  87     wait_for_pusi_(true),
  88     previous_pts_valid_(false),
  89     previous_pts_(0),
  90     previous_dts_valid_(false),
  91     previous_dts_(0) {
  92   DCHECK(es_parser_);
  93 }
  94
  95 TsSectionPes::~TsSectionPes() {
  96 }
  97
  98 bool TsSectionPes::Parse(bool payload_unit_start_indicator,
  99                              const uint8* buf, int size) {
 100   // Ignore partial PES.
 101   if (wait_for_pusi_ && !payload_unit_start_indicator)
 102     return true;
 103
 104   bool parse_result = true;
 105   if (payload_unit_start_indicator) {
 106     // Try emitting a packet since we might have a pending PES packet
 107     // with an undefined size.
 108     // In this case, a unit is emitted when the next unit is coming.
 109     int raw_pes_size;
 110     const uint8* raw_pes;
 111     pes_byte_queue_.Peek(&raw_pes, &raw_pes_size);
 112     if (raw_pes_size > 0)
 113       parse_result = Emit(true);
 114
 115     // Reset the state.
 116     ResetPesState();
 117
 118     // Update the state.
 119     wait_for_pusi_ = false;
 120   }
 121
 122   // Add the data to the parser state.
 123   if (size > 0)
 124     pes_byte_queue_.Push(buf, size);
 125
 126   // Try emitting the current PES packet.
 127   return (parse_result && Emit(false));
 128 }
 129
 130 void TsSectionPes::Flush() {
 131   // Try emitting a packet since we might have a pending PES packet
 132   // with an undefined size.
 133   Emit(true);
 134
 135   // Flush the underlying ES parser.
 136   es_parser_->Flush();
 137 }
 138
 139 void TsSectionPes::Reset() {
 140   ResetPesState();
 141
 142   previous_pts_valid_ = false;
 143   previous_pts_ = 0;
 144   previous_dts_valid_ = false;
 145   previous_dts_ = 0;
 146
 147   es_parser_->Reset();
 148 }
 149
 150 bool TsSectionPes::Emit(bool emit_for_unknown_size) {
 151   int raw_pes_size;
 152   const uint8* raw_pes;
 153   pes_byte_queue_.Peek(&raw_pes, &raw_pes_size);
 154
 155   // A PES should be at least 6 bytes.
 156   // Wait for more data to come if not enough bytes.
 157   if (raw_pes_size < 6)
 158     return true;
 159
 160   // Check whether we have enough data to start parsing.
 161   int pes_packet_length =
 162       (static_cast<int>(raw_pes[4]) << 8) |
 163       (static_cast<int>(raw_pes[5]));
 164   if ((pes_packet_length == 0 && !emit_for_unknown_size) ||
 165       (pes_packet_length != 0 && raw_pes_size < pes_packet_length + 6)) {
 166     // Wait for more data to come either because:
 167     // - there are not enough bytes,
 168     // - or the PES size is unknown and the "force emit" flag is not set.
 169     //   (PES size might be unknown for video PES packet).
 170     return true;
 171   }
 172   DVLOG(LOG_LEVEL_PES) << "pes_packet_length=" << pes_packet_length;
 173
 174   // Parse the packet.
 175   bool parse_result = ParseInternal(raw_pes, raw_pes_size);
 176
 177   // Reset the state.
 178   ResetPesState();
 179
 180   return parse_result;
 181 }
 182
 183 bool TsSectionPes::ParseInternal(const uint8* raw_pes, int raw_pes_size) {
 184   BitReader bit_reader(raw_pes, raw_pes_size);
 185
 186   // Read up to the pes_packet_length (6 bytes).
 187   int packet_start_code_prefix;
 188   int stream_id;
 189   int pes_packet_length;
 190   RCHECK(bit_reader.ReadBits(24, &packet_start_code_prefix));
 191   RCHECK(bit_reader.ReadBits(8, &stream_id));
 192   RCHECK(bit_reader.ReadBits(16, &pes_packet_length));
 193
 194   RCHECK(packet_start_code_prefix == kPesStartCode);
 195   DVLOG(LOG_LEVEL_PES) << "stream_id=" << std::hex << stream_id << std::dec;
 196   if (pes_packet_length == 0)
 197     pes_packet_length = bit_reader.bits_available() / 8;
 198
 199   // Ignore the PES for unknown stream IDs.
 200   // See ITU H.222 Table 2-22 "Stream_id assignments"
 201   bool is_audio_stream_id = ((stream_id & 0xe0) == 0xc0);
 202   bool is_video_stream_id = ((stream_id & 0xf0) == 0xe0);
 203   if (!is_audio_stream_id && !is_video_stream_id)
 204     return true;
 205
 206   // Read up to "pes_header_data_length".
 207   int dummy_2;
 208   int PES_scrambling_control;
 209   int PES_priority;
 210   int data_alignment_indicator;
 211   int copyright;
 212   int original_or_copy;
 213   int pts_dts_flags;
 214   int escr_flag;
 215   int es_rate_flag;
 216   int dsm_trick_mode_flag;
 217   int additional_copy_info_flag;
 218   int pes_crc_flag;
 219   int pes_extension_flag;
 220   int pes_header_data_length;
 221   RCHECK(bit_reader.ReadBits(2, &dummy_2));
 222   RCHECK(dummy_2 == 0x2);
 223   RCHECK(bit_reader.ReadBits(2, &PES_scrambling_control));
 224   RCHECK(bit_reader.ReadBits(1, &PES_priority));
 225   RCHECK(bit_reader.ReadBits(1, &data_alignment_indicator));
 226   RCHECK(bit_reader.ReadBits(1, &copyright));
 227   RCHECK(bit_reader.ReadBits(1, &original_or_copy));
 228   RCHECK(bit_reader.ReadBits(2, &pts_dts_flags));
 229   RCHECK(bit_reader.ReadBits(1, &escr_flag));
 230   RCHECK(bit_reader.ReadBits(1, &es_rate_flag));
 231   RCHECK(bit_reader.ReadBits(1, &dsm_trick_mode_flag));
 232   RCHECK(bit_reader.ReadBits(1, &additional_copy_info_flag));
 233   RCHECK(bit_reader.ReadBits(1, &pes_crc_flag));
 234   RCHECK(bit_reader.ReadBits(1, &pes_extension_flag));
 235   RCHECK(bit_reader.ReadBits(8, &pes_header_data_length));
 236   int pes_header_start_size = bit_reader.bits_available() / 8;
 237
 238   // Compute the size and the offset of the ES payload.
 239   // "6" for the 6 bytes read before and including |pes_packet_length|.
 240   // "3" for the 3 bytes read before and including |pes_header_data_length|.
 241   int es_size = pes_packet_length - 3 - pes_header_data_length;
 242   int es_offset = 6 + 3 + pes_header_data_length;
 243   RCHECK(es_size >= 0);
 244   RCHECK(es_offset + es_size <= raw_pes_size);
 245
 246   // Read the timing information section.
 247   bool is_pts_valid = false;
 248   bool is_dts_valid = false;
 249   int64 pts_section = 0;
 250   int64 dts_section = 0;
 251   if (pts_dts_flags == 0x2) {
 252     RCHECK(bit_reader.ReadBits(40, &pts_section));
 253     RCHECK((((pts_section >> 36) & 0xf) == 0x2) &&
 254            IsTimestampSectionValid(pts_section));
 255     is_pts_valid = true;
 256   }
 257   if (pts_dts_flags == 0x3) {
 258     RCHECK(bit_reader.ReadBits(40, &pts_section));
 259     RCHECK(bit_reader.ReadBits(40, &dts_section));
 260     RCHECK((((pts_section >> 36) & 0xf) == 0x3) &&
 261            IsTimestampSectionValid(pts_section));
 262     RCHECK((((dts_section >> 36) & 0xf) == 0x1) &&
 263            IsTimestampSectionValid(dts_section));
 264     is_pts_valid = true;
 265     is_dts_valid = true;
 266   }
 267
 268   // Convert and unroll the timestamps.
 269   base::TimeDelta media_pts(kNoTimestamp());
 270   base::TimeDelta media_dts(kNoTimestamp());
 271   if (is_pts_valid) {
 272     int64 pts = ConvertTimestampSectionToTimestamp(pts_section);
 273     if (previous_pts_valid_)
 274       pts = UnrollTimestamp(previous_pts_, pts);
 275     previous_pts_ = pts;
 276     previous_pts_valid_ = true;
 277     media_pts = base::TimeDelta::FromMicroseconds((1000 * pts) / 90);
 278   }
 279   if (is_dts_valid) {
 280     int64 dts = ConvertTimestampSectionToTimestamp(dts_section);
 281     if (previous_dts_valid_)
 282       dts = UnrollTimestamp(previous_dts_, dts);
 283     previous_dts_ = dts;
 284     previous_dts_valid_ = true;
 285     media_dts = base::TimeDelta::FromMicroseconds((1000 * dts) / 90);
 286   }
 287
 288   // Discard the rest of the PES packet header.
 289   // TODO(damienv): check if some info of the PES packet header are useful.
 290   DCHECK_EQ(bit_reader.bits_available() % 8, 0);
 291   int pes_header_remaining_size = pes_header_data_length -
 292       (pes_header_start_size - bit_reader.bits_available() / 8);
 293   RCHECK(pes_header_remaining_size >= 0);
 294
 295   // Read the PES packet.
 296   DVLOG(LOG_LEVEL_PES)
 297       << "Emit a reassembled PES:"
 298       << " size=" << es_size
 299       << " pts=" << media_pts.InMilliseconds()
 300       << " dts=" << media_dts.InMilliseconds()
 301       << " data_alignment_indicator=" << data_alignment_indicator;
 302   return es_parser_->Parse(&raw_pes[es_offset], es_size, media_pts, media_dts);
 303 }
 304
 305 void TsSectionPes::ResetPesState() {
 306   pes_byte_queue_.Reset();
 307   wait_for_pusi_ = true;
 308 }
 309
 310 }  // namespace mp2t
 311 }  // namespace media
 312