Mpeg2 TS stream parser for media source.

media/mp2t/ts_section_pes.cc

+// Copyright (c) 2013 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "media/mp2t/ts_section_pes.h"
+
+#include "base/logging.h"
+#include "base/strings/string_number_conversions.h"
+#include "media/base/bit_reader.h"
+#include "media/base/buffers.h"
+#include "media/mp2t/es_parser.h"
+#include "media/mp2t/mp2t_common.h"
+
+static const int kPesStartCode = 0x000001;
+
+// Given that |time| is coded using 33 bits,
+// UnrollTimestamp returns the corresponding unrolled timestamp.
+// The unrolled timestamp is defined by:
+// |time| + k * (2 ^ 33)
+// where k is estimated so that the unrolled timestamp
+// is as close as possible to |previous_unrolled_time|.
+static int64 UnrollTimestamp(int64 previous_unrolled_time, int64 time) {
+  // Mpeg2 TS timestamps have an accuracy of 33 bits.
+  const int nbits = 33;
+
+  // |timestamp| has a precision of |nbits|
+  // so make sure the highest bits are set to 0.
+  DCHECK_EQ((time >> nbits), 0);
+
+  // Consider 3 possibilities to estimate the missing high bits of |time|.
+  int64 previous_unrolled_time_high =
+      (previous_unrolled_time >> nbits);
+  int64 time0 = ((previous_unrolled_time_high - 1) << nbits) | time;
+  int64 time1 = ((previous_unrolled_time_high + 0) << nbits) | time;
+  int64 time2 = ((previous_unrolled_time_high + 1) << nbits) | time;
+
+  // Select the min absolute difference with the current time
+  // so as to ensure time continuity.
+  int64 diff0 = time0 - previous_unrolled_time;
+  int64 diff1 = time1 - previous_unrolled_time;
+  int64 diff2 = time2 - previous_unrolled_time;
+  if (diff0 < 0)
+    diff0 = -diff0;
+  if (diff1 < 0)
+    diff1 = -diff1;
+  if (diff2 < 0)
+    diff2 = -diff2;
+
+  int64 unrolled_time;
+  int64 min_diff;
+  if (diff1 < diff0) {
+    unrolled_time = time1;
+    min_diff = diff1;
+  } else {
+    unrolled_time = time0;
+    min_diff = diff0;
+  }
+  if (diff2 < min_diff)
+    unrolled_time = time2;
+
+  return unrolled_time;
+}
+
+static bool IsTimestampSectionValid(int64 timestamp_section) {
+  // |pts_section| has 40 bits:
+  // - starting with either '0010' or '0011' or '0001'
+  // - and ending with a marker bit.
+  // See ITU H.222 standard - PES section.
+
+  // Verify that all the marker bits are set to one.
+  return ((timestamp_section & 0x1) != 0) &&
+         ((timestamp_section & 0x10000) != 0) &&
+         ((timestamp_section & 0x100000000) != 0);
+}
+
+static int64 ConvertTimestampSectionToTimestamp(int64 timestamp_section) {
+  return (((timestamp_section >> 33) & 0x7) << 30) |
+         (((timestamp_section >> 17) & 0x7fff) << 15) |
+         (((timestamp_section >> 1) & 0x7fff) << 0);
+}
+
+namespace media {
+namespace mp2t {
+
+TsSectionPes::TsSectionPes(scoped_ptr<EsParser> es_parser)
+  : es_parser_(es_parser.release()),
+    wait_for_pusi_(true),
+    previous_pts_valid_(false),
+    previous_pts_(0),
+    previous_dts_valid_(false),
+    previous_dts_(0) {
+  DCHECK(es_parser_);
+}
+
+TsSectionPes::~TsSectionPes() {
+}
+
+bool TsSectionPes::Parse(bool payload_unit_start_indicator,
+                             const uint8* buf, int size) {
+  // Ignore partial PES.
+  if (wait_for_pusi_ && !payload_unit_start_indicator)
+    return true;
+
+  bool parse_result = true;
+  if (payload_unit_start_indicator) {
+    // Try emitting a packet since we might have a pending PES packet
+    // with an undefined size.
+    // In this case, a unit is emitted when the next unit is coming.
+    int raw_pes_size;
+    const uint8* raw_pes;
+    pes_byte_queue_.Peek(&raw_pes, &raw_pes_size);
+    if (raw_pes_size > 0)
+      parse_result = Emit(true);
+
+    // Reset the state.
+    ResetPesState();
+
+    // Update the state.
+    wait_for_pusi_ = false;
+  }
+
+  // Add the data to the parser state.
+  if (size > 0)
+    pes_byte_queue_.Push(buf, size);
+
+  // Try emitting the current PES packet.
+  parse_result = parse_result && Emit(false);

[acolwell GONE FROM CHROMIUM, 2013/09/18 01:46:05]

nit: just return here since you don't use the updated value of parse_result

[damienv1, 2013/09/18 21:40:17]

Done.

+
+  return parse_result;
+}
+
+void TsSectionPes::Flush() {
+  // Try emitting a packet since we might have a pending PES packet
+  // with an undefined size.
+  Emit(true);
+
+  // Flush the underlying ES parser.
+  es_parser_->Flush();
+}
+
+void TsSectionPes::Reset() {
+  ResetPesState();
+
+  previous_pts_valid_ = false;
+  previous_pts_ = 0;
+  previous_dts_valid_ = false;
+  previous_dts_ = 0;
+
+  es_parser_->Reset();
+}
+
+bool TsSectionPes::Emit(bool emit_for_unknown_size) {
+  int raw_pes_size;
+  const uint8* raw_pes;
+  pes_byte_queue_.Peek(&raw_pes, &raw_pes_size);
+
+  // A PES should be at least 6 bytes.
+  // Wait for more data to come if not enough bytes.
+  if (raw_pes_size < 6)
+    return true;
+
+  // Check whether we have enough data to start parsing.
+  int pes_packet_length =
+      (static_cast<int>(raw_pes[4]) << 8) |
+      (static_cast<int>(raw_pes[5]));
+  if ((pes_packet_length == 0 && !emit_for_unknown_size) ||
+      (pes_packet_length != 0 && raw_pes_size < pes_packet_length + 6)) {
+    // Wait for more data to come either because:
+    // - there are not enough bytes,
+    // - or the PES size is unknown and the "force emit" flag is not set.
+    //   (PES size might be unknown for video PES packet).
+    return true;
+  }
+  DVLOG(LOG_LEVEL_PES) << "pes_packet_length=" << pes_packet_length;
+
+  // Parse the packet.
+  bool parse_result = ParseInternal(raw_pes, raw_pes_size);
+
+  // Reset the state.
+  ResetPesState();
+
+  return parse_result;
+}
+
+bool TsSectionPes::ParseInternal(const uint8* raw_pes, int raw_pes_size) {
+  BitReader bit_reader(raw_pes, raw_pes_size);
+
+  // Read up to the pes_packet_length (6 bytes).
+  int packet_start_code_prefix;
+  int stream_id;
+  int pes_packet_length;
+  RCHECK(bit_reader.ReadBits(24, &packet_start_code_prefix));
+  RCHECK(bit_reader.ReadBits(8, &stream_id));
+  RCHECK(bit_reader.ReadBits(16, &pes_packet_length));
+
+  RCHECK(packet_start_code_prefix == kPesStartCode);
+  DVLOG(LOG_LEVEL_PES) << "stream_id=" << std::hex << stream_id << std::dec;
+  if (pes_packet_length == 0)
+    pes_packet_length = bit_reader.bits_available() / 8;
+
+  // Ignore the PES for unknown stream IDs.
+  // See ITU H.222 Table 2-22 "Stream_id assignments"
+  bool is_audio_stream_id = ((stream_id & 0xe0) == 0xc0);
+  bool is_video_stream_id = ((stream_id & 0xf0) == 0xe0);
+  if (!is_audio_stream_id && !is_video_stream_id)
+    return true;
+
+  // Read up to "pes_header_data_length".
+  int dummy_2;
+  int PES_scrambling_control;
+  bool PES_priority;
+  bool data_alignment_indicator;
+  bool copyright;
+  bool original_or_copy;
+  int pts_dts_flags;
+  bool escr_flag;
+  bool es_rate_flag;
+  bool dsm_trick_mode_flag;
+  bool additional_copy_info_flag;
+  bool pes_crc_flag;
+  bool pes_extension_flag;
+  int pes_header_data_length;
+  RCHECK(bit_reader.ReadBits(2, &dummy_2));
+  RCHECK(dummy_2 == 0x2);
+  RCHECK(bit_reader.ReadBits(2, &PES_scrambling_control));
+  RCHECK(bit_reader.ReadBits(1, &PES_priority));
+  RCHECK(bit_reader.ReadBits(1, &data_alignment_indicator));
+  RCHECK(bit_reader.ReadBits(1, &copyright));
+  RCHECK(bit_reader.ReadBits(1, &original_or_copy));
+  RCHECK(bit_reader.ReadBits(2, &pts_dts_flags));
+  RCHECK(bit_reader.ReadBits(1, &escr_flag));
+  RCHECK(bit_reader.ReadBits(1, &es_rate_flag));
+  RCHECK(bit_reader.ReadBits(1, &dsm_trick_mode_flag));
+  RCHECK(bit_reader.ReadBits(1, &additional_copy_info_flag));
+  RCHECK(bit_reader.ReadBits(1, &pes_crc_flag));
+  RCHECK(bit_reader.ReadBits(1, &pes_extension_flag));
+  RCHECK(bit_reader.ReadBits(8, &pes_header_data_length));
+  int pes_header_start_size = bit_reader.bits_available() / 8;
+
+  // Compute the size and the offset of the ES payload.
+  // "6" for the 6 bytes read before and including |pes_packet_length|.
+  // "3" for the 3 bytes read before and including |pes_header_data_length|.
+  int es_size = pes_packet_length - 3 - pes_header_data_length;
+  int es_offset = 6 + 3 + pes_header_data_length;
+  RCHECK(es_size >= 0);
+  RCHECK(es_offset + es_size <= raw_pes_size);
+
+  // Read the timing information section.
+  bool is_pts_valid = false;
+  bool is_dts_valid = false;
+  int64 pts_section = 0;
+  int64 dts_section = 0;
+  if (pts_dts_flags == 0x2) {
+    RCHECK(bit_reader.ReadBits(40, &pts_section));
+    RCHECK((((pts_section >> 36) & 0xf) == 0x2) &&
+           IsTimestampSectionValid(pts_section));
+    is_pts_valid = true;
+  }
+  if (pts_dts_flags == 0x3) {
+    RCHECK(bit_reader.ReadBits(40, &pts_section));
+    RCHECK(bit_reader.ReadBits(40, &dts_section));
+    RCHECK((((pts_section >> 36) & 0xf) == 0x3) &&
+           IsTimestampSectionValid(pts_section));
+    RCHECK((((dts_section >> 36) & 0xf) == 0x1) &&
+           IsTimestampSectionValid(dts_section));
+    is_pts_valid = true;
+    is_dts_valid = true;
+  }
+
+  // Convert and unroll the timestamps.
+  base::TimeDelta media_pts(kNoTimestamp());
+  base::TimeDelta media_dts(kNoTimestamp());
+  if (is_pts_valid) {
+    int64 pts = ConvertTimestampSectionToTimestamp(pts_section);
+    if (previous_pts_valid_)
+      pts = UnrollTimestamp(previous_pts_, pts);
+    previous_pts_ = pts;
+    previous_pts_valid_ = true;
+    media_pts = base::TimeDelta::FromMicroseconds((1000 * pts) / 90);
+  }
+  if (is_dts_valid) {
+    int64 dts = ConvertTimestampSectionToTimestamp(dts_section);
+    if (previous_dts_valid_)
+      dts = UnrollTimestamp(previous_dts_, dts);
+    previous_dts_ = dts;
+    previous_dts_valid_ = true;
+    media_dts = base::TimeDelta::FromMicroseconds((1000 * dts) / 90);
+  }
+
+  // Discard the rest of the PES packet header.
+  // TODO(damienv): check if some info of the PES packet header are useful.
+  DCHECK_EQ(bit_reader.bits_available() % 8, 0);
+  int pes_header_remaining_size = pes_header_data_length -
+      (pes_header_start_size - bit_reader.bits_available() / 8);
+  RCHECK(pes_header_remaining_size >= 0);
+
+  // Read the PES packet.
+  DVLOG(LOG_LEVEL_PES)
+      << "Emit a reassembled PES:"
+      << " size=" << es_size
+      << " pts=" << media_pts.InMilliseconds()
+      << " dts=" << media_dts.InMilliseconds()
+      << " data_alignment_indicator=" << data_alignment_indicator;
+  return es_parser_->Parse(&raw_pes[es_offset], es_size, media_pts, media_dts);
+}
+
+void TsSectionPes::ResetPesState() {
+  pes_byte_queue_.Reset();
+  wait_for_pusi_ = true;
+}
+
+}  // namespace mp2t
+}  // namespace media
+