Add H264 bitstream rewriting to limit frame reordering marker in header

webrtc/modules/video_coding/utility/h264_bitstream_parser.cc

Index: webrtc/modules/video_coding/utility/h264_bitstream_parser.cc
diff --git a/webrtc/modules/video_coding/utility/h264_bitstream_parser.cc b/webrtc/modules/video_coding/utility/h264_bitstream_parser.cc
index 9102a6a62d54cf8899369cf61f9eb64e519ef53e..97cd0038695ca5f30fe4bccb48b32b1392b02b67 100644
--- a/webrtc/modules/video_coding/utility/h264_bitstream_parser.cc
+++ b/webrtc/modules/video_coding/utility/h264_bitstream_parser.cc
@@ -15,74 +15,11 @@
 #include "webrtc/base/bitbuffer.h"
 #include "webrtc/base/bytebuffer.h"
 #include "webrtc/base/checks.h"
+
+#include "webrtc/common_video/h264/h264_common.h"
 #include "webrtc/base/logging.h"
 
 namespace webrtc {
-namespace {
-// The size of a NALU header {0 0 0 1}.
-static const size_t kNaluHeaderSize = 4;
-
-// The size of a NALU header plus the type byte.
-static const size_t kNaluHeaderAndTypeSize = kNaluHeaderSize + 1;
-
-// The NALU type.
-static const uint8_t kNaluSps = 0x7;
-static const uint8_t kNaluPps = 0x8;
-static const uint8_t kNaluIdr = 0x5;
-static const uint8_t kNaluTypeMask = 0x1F;
-
-static const uint8_t kSliceTypeP = 0x0;
-static const uint8_t kSliceTypeB = 0x1;
-static const uint8_t kSliceTypeSp = 0x3;
-
-// Returns a vector of the NALU start sequences (0 0 0 1) in the given buffer.
-std::vector<size_t> FindNaluStartSequences(const uint8_t* buffer,
-                                           size_t buffer_size) {
-  std::vector<size_t> sequences;
-  // This is sorta like Boyer-Moore, but with only the first optimization step:
-  // given a 4-byte sequence we're looking at, if the 4th byte isn't 1 or 0,
-  // skip ahead to the next 4-byte sequence. 0s and 1s are relatively rare, so
-  // this will skip the majority of reads/checks.
-  const uint8_t* end = buffer + buffer_size - 4;
-  for (const uint8_t* head = buffer; head < end;) {
-    if (head[3] > 1) {
-      head += 4;
-    } else if (head[3] == 1 && head[2] == 0 && head[1] == 0 && head[0] == 0) {
-      sequences.push_back(static_cast<size_t>(head - buffer));
-      head += 4;
-    } else {
-      head++;
-    }
-  }
-
-  return sequences;
-}
-}  // namespace
-
-// Parses RBSP from source bytes. Removes emulation bytes, but leaves the
-// rbsp_trailing_bits() in the stream, since none of the parsing reads all the
-// way to the end of a parsed RBSP sequence. When writing, that means the
-// rbsp_trailing_bits() should be preserved and don't need to be restored (i.e.
-// the rbsp_stop_one_bit, which is just a 1, then zero padded), and alignment
-// should "just work".
-// TODO(pbos): Make parsing RBSP something that can be integrated into BitBuffer
-// so we don't have to copy the entire frames when only interested in the
-// headers.
-rtc::ByteBufferWriter* ParseRbsp(const uint8_t* bytes, size_t length) {
-  // Copied from webrtc::H264SpsParser::Parse.
-  rtc::ByteBufferWriter* rbsp_buffer = new rtc::ByteBufferWriter();
-  for (size_t i = 0; i < length;) {
-    if (length - i >= 3 && bytes[i] == 0 && bytes[i + 1] == 0 &&
-        bytes[i + 2] == 3) {
-      rbsp_buffer->WriteBytes(reinterpret_cast<const char*>(bytes) + i, 2);
-      i += 3;
-    } else {
-      rbsp_buffer->WriteBytes(reinterpret_cast<const char*>(bytes) + i, 1);
-      i++;
-    }
-  }
-  return rbsp_buffer;
-}
 
 #define RETURN_FALSE_ON_FAIL(x)       \
   if (!(x)) {                         \
@@ -90,242 +27,23 @@ rtc::ByteBufferWriter* ParseRbsp(const uint8_t* bytes, size_t length) {
     return false;                     \
   }
 
-H264BitstreamParser::PpsState::PpsState() {}
-
-H264BitstreamParser::SpsState::SpsState() {}
-
-// These functions are similar to webrtc::H264SpsParser::Parse, and based on the
-// same version of the H.264 standard. You can find it here:
-// http://www.itu.int/rec/T-REC-H.264
-bool H264BitstreamParser::ParseSpsNalu(const uint8_t* sps, size_t length) {
-  // Reset SPS state.
-  sps_ = SpsState();
-  sps_parsed_ = false;
-  // Parse out the SPS RBSP. It should be small, so it's ok that we create a
-  // copy. We'll eventually write this back.
-  std::unique_ptr<rtc::ByteBufferWriter> sps_rbsp(
-      ParseRbsp(sps + kNaluHeaderAndTypeSize, length - kNaluHeaderAndTypeSize));
-  rtc::BitBuffer sps_parser(reinterpret_cast<const uint8_t*>(sps_rbsp->Data()),
-                            sps_rbsp->Length());
-
-  uint8_t byte_tmp;
-  uint32_t golomb_tmp;
-  uint32_t bits_tmp;
-
-  // profile_idc: u(8).
-  uint8_t profile_idc;
-  RETURN_FALSE_ON_FAIL(sps_parser.ReadUInt8(&profile_idc));
-  // constraint_set0_flag through constraint_set5_flag + reserved_zero_2bits
-  // 1 bit each for the flags + 2 bits = 8 bits = 1 byte.
-  RETURN_FALSE_ON_FAIL(sps_parser.ReadUInt8(&byte_tmp));
-  // level_idc: u(8)
-  RETURN_FALSE_ON_FAIL(sps_parser.ReadUInt8(&byte_tmp));
-  // seq_parameter_set_id: ue(v)
-  RETURN_FALSE_ON_FAIL(sps_parser.ReadExponentialGolomb(&golomb_tmp));
-  sps_.separate_colour_plane_flag = 0;
-  // See if profile_idc has chroma format information.
-  if (profile_idc == 100 || profile_idc == 110 || profile_idc == 122 ||
-      profile_idc == 244 || profile_idc == 44 || profile_idc == 83 ||
-      profile_idc == 86 || profile_idc == 118 || profile_idc == 128 ||
-      profile_idc == 138 || profile_idc == 139 || profile_idc == 134) {
-    // chroma_format_idc: ue(v)
-    uint32_t chroma_format_idc;
-    RETURN_FALSE_ON_FAIL(sps_parser.ReadExponentialGolomb(&chroma_format_idc));
-    if (chroma_format_idc == 3) {
-      // separate_colour_plane_flag: u(1)
-      RETURN_FALSE_ON_FAIL(
-          sps_parser.ReadBits(&sps_.separate_colour_plane_flag, 1));
-    }
-    // bit_depth_luma_minus8: ue(v)
-    RETURN_FALSE_ON_FAIL(sps_parser.ReadExponentialGolomb(&golomb_tmp));
-    // bit_depth_chroma_minus8: ue(v)
-    RETURN_FALSE_ON_FAIL(sps_parser.ReadExponentialGolomb(&golomb_tmp));
-    // qpprime_y_zero_transform_bypass_flag: u(1)
-    RETURN_FALSE_ON_FAIL(sps_parser.ReadBits(&bits_tmp, 1));
-    // seq_scaling_matrix_present_flag: u(1)
-    uint32_t seq_scaling_matrix_present_flag;
-    RETURN_FALSE_ON_FAIL(
-        sps_parser.ReadBits(&seq_scaling_matrix_present_flag, 1));
-    if (seq_scaling_matrix_present_flag) {
-      // seq_scaling_list_present_flags. Either 8 or 12, depending on
-      // chroma_format_idc.
-      uint32_t seq_scaling_list_present_flags;
-      if (chroma_format_idc != 3) {
-        RETURN_FALSE_ON_FAIL(
-            sps_parser.ReadBits(&seq_scaling_list_present_flags, 8));
-      } else {
-        RETURN_FALSE_ON_FAIL(
-            sps_parser.ReadBits(&seq_scaling_list_present_flags, 12));
-      }
-      // TODO(pbos): Support parsing scaling lists if they're seen in practice.
-      RTC_CHECK(seq_scaling_list_present_flags == 0)
-          << "SPS contains scaling lists, which are unsupported.";
-    }
-  }
-  // log2_max_frame_num_minus4: ue(v)
-  RETURN_FALSE_ON_FAIL(
-      sps_parser.ReadExponentialGolomb(&sps_.log2_max_frame_num_minus4));
-  // pic_order_cnt_type: ue(v)
-  RETURN_FALSE_ON_FAIL(
-      sps_parser.ReadExponentialGolomb(&sps_.pic_order_cnt_type));
-
-  if (sps_.pic_order_cnt_type == 0) {
-    // log2_max_pic_order_cnt_lsb_minus4: ue(v)
-    RETURN_FALSE_ON_FAIL(sps_parser.ReadExponentialGolomb(
-        &sps_.log2_max_pic_order_cnt_lsb_minus4));
-  } else if (sps_.pic_order_cnt_type == 1) {
-    // delta_pic_order_always_zero_flag: u(1)
-    RETURN_FALSE_ON_FAIL(
-        sps_parser.ReadBits(&sps_.delta_pic_order_always_zero_flag, 1));
-    // offset_for_non_ref_pic: se(v)
-    RETURN_FALSE_ON_FAIL(sps_parser.ReadExponentialGolomb(&golomb_tmp));
-    // offset_for_top_to_bottom_field: se(v)
-    RETURN_FALSE_ON_FAIL(sps_parser.ReadExponentialGolomb(&golomb_tmp));
-    uint32_t num_ref_frames_in_pic_order_cnt_cycle;
-    // num_ref_frames_in_pic_order_cnt_cycle: ue(v)
-    RETURN_FALSE_ON_FAIL(sps_parser.ReadExponentialGolomb(
-        &num_ref_frames_in_pic_order_cnt_cycle));
-    for (uint32_t i = 0; i < num_ref_frames_in_pic_order_cnt_cycle; i++) {
-      // offset_for_ref_frame[i]: se(v)
-      RETURN_FALSE_ON_FAIL(sps_parser.ReadExponentialGolomb(&golomb_tmp));
-    }
-  }
-  // max_num_ref_frames: ue(v)
-  RETURN_FALSE_ON_FAIL(sps_parser.ReadExponentialGolomb(&golomb_tmp));
-  // gaps_in_frame_num_value_allowed_flag: u(1)
-  RETURN_FALSE_ON_FAIL(sps_parser.ReadBits(&bits_tmp, 1));
-  // pic_width_in_mbs_minus1: ue(v)
-  RETURN_FALSE_ON_FAIL(sps_parser.ReadExponentialGolomb(&golomb_tmp));
-  // pic_height_in_map_units_minus1: ue(v)
-  RETURN_FALSE_ON_FAIL(sps_parser.ReadExponentialGolomb(&golomb_tmp));
-  // frame_mbs_only_flag: u(1)
-  RETURN_FALSE_ON_FAIL(sps_parser.ReadBits(&sps_.frame_mbs_only_flag, 1));
-  sps_parsed_ = true;
-  return true;
-}
-
-bool H264BitstreamParser::ParsePpsNalu(const uint8_t* pps, size_t length) {
-  RTC_CHECK(sps_parsed_);
-  // We're starting a new stream, so reset picture type rewriting values.
-  pps_ = PpsState();
-  pps_parsed_ = false;
-  std::unique_ptr<rtc::ByteBufferWriter> buffer(
-      ParseRbsp(pps + kNaluHeaderAndTypeSize, length - kNaluHeaderAndTypeSize));
-  rtc::BitBuffer parser(reinterpret_cast<const uint8_t*>(buffer->Data()),
-                        buffer->Length());
-
-  uint32_t bits_tmp;
-  uint32_t golomb_ignored;
-  // pic_parameter_set_id: ue(v)
-  RETURN_FALSE_ON_FAIL(parser.ReadExponentialGolomb(&golomb_ignored));
-  // seq_parameter_set_id: ue(v)
-  RETURN_FALSE_ON_FAIL(parser.ReadExponentialGolomb(&golomb_ignored));
-  // entropy_coding_mode_flag: u(1)
-  uint32_t entropy_coding_mode_flag;
-  RETURN_FALSE_ON_FAIL(parser.ReadBits(&entropy_coding_mode_flag, 1));
-  // TODO(pbos): Implement CABAC support if spotted in the wild.
-  RTC_CHECK(entropy_coding_mode_flag == 0)
-      << "Don't know how to parse CABAC streams.";
-  // bottom_field_pic_order_in_frame_present_flag: u(1)
-  uint32_t bottom_field_pic_order_in_frame_present_flag;
-  RETURN_FALSE_ON_FAIL(
-      parser.ReadBits(&bottom_field_pic_order_in_frame_present_flag, 1));
-  pps_.bottom_field_pic_order_in_frame_present_flag =
-      bottom_field_pic_order_in_frame_present_flag != 0;
-
-  // num_slice_groups_minus1: ue(v)
-  uint32_t num_slice_groups_minus1;
-  RETURN_FALSE_ON_FAIL(parser.ReadExponentialGolomb(&num_slice_groups_minus1));
-  if (num_slice_groups_minus1 > 0) {
-    uint32_t slice_group_map_type;
-    // slice_group_map_type: ue(v)
-    RETURN_FALSE_ON_FAIL(parser.ReadExponentialGolomb(&slice_group_map_type));
-    if (slice_group_map_type == 0) {
-      for (uint32_t i_group = 0; i_group <= num_slice_groups_minus1;
-           ++i_group) {
-        // run_length_minus1[iGroup]: ue(v)
-        RETURN_FALSE_ON_FAIL(parser.ReadExponentialGolomb(&golomb_ignored));
-      }
-    } else if (slice_group_map_type == 2) {
-      for (uint32_t i_group = 0; i_group <= num_slice_groups_minus1;
-           ++i_group) {
-        // top_left[iGroup]: ue(v)
-        RETURN_FALSE_ON_FAIL(parser.ReadExponentialGolomb(&golomb_ignored));
-        // bottom_right[iGroup]: ue(v)
-        RETURN_FALSE_ON_FAIL(parser.ReadExponentialGolomb(&golomb_ignored));
-      }
-    } else if (slice_group_map_type == 3 || slice_group_map_type == 4 ||
-               slice_group_map_type == 5) {
-      // slice_group_change_direction_flag: u(1)
-      RETURN_FALSE_ON_FAIL(parser.ReadBits(&bits_tmp, 1));
-      // slice_group_change_rate_minus1: ue(v)
-      RETURN_FALSE_ON_FAIL(parser.ReadExponentialGolomb(&golomb_ignored));
-    } else if (slice_group_map_type == 6) {
-      // pic_size_in_map_units_minus1: ue(v)
-      uint32_t pic_size_in_map_units_minus1;
-      RETURN_FALSE_ON_FAIL(
-          parser.ReadExponentialGolomb(&pic_size_in_map_units_minus1));
-      uint32_t slice_group_id_bits = 0;
-      uint32_t num_slice_groups = num_slice_groups_minus1 + 1;
-      // If num_slice_groups is not a power of two an additional bit is required
-      // to account for the ceil() of log2() below.
-      if ((num_slice_groups & (num_slice_groups - 1)) != 0)
-        ++slice_group_id_bits;
-      while (num_slice_groups > 0) {
-        num_slice_groups >>= 1;
-        ++slice_group_id_bits;
-      }
-      for (uint32_t i = 0; i <= pic_size_in_map_units_minus1; i++) {
-        // slice_group_id[i]: u(v)
-        // Represented by ceil(log2(num_slice_groups_minus1 + 1)) bits.
-        RETURN_FALSE_ON_FAIL(parser.ReadBits(&bits_tmp, slice_group_id_bits));
-      }
-    }
-  }
-  // num_ref_idx_l0_default_active_minus1: ue(v)
-  RETURN_FALSE_ON_FAIL(parser.ReadExponentialGolomb(&golomb_ignored));
-  // num_ref_idx_l1_default_active_minus1: ue(v)
-  RETURN_FALSE_ON_FAIL(parser.ReadExponentialGolomb(&golomb_ignored));
-  // weighted_pred_flag: u(1)
-  uint32_t weighted_pred_flag;
-  RETURN_FALSE_ON_FAIL(parser.ReadBits(&weighted_pred_flag, 1));
-  pps_.weighted_pred_flag = weighted_pred_flag != 0;
-  // weighted_bipred_idc: u(2)
-  RETURN_FALSE_ON_FAIL(parser.ReadBits(&pps_.weighted_bipred_idc, 2));
-
-  // pic_init_qp_minus26: se(v)
-  RETURN_FALSE_ON_FAIL(
-      parser.ReadSignedExponentialGolomb(&pps_.pic_init_qp_minus26));
-  // pic_init_qs_minus26: se(v)
-  RETURN_FALSE_ON_FAIL(parser.ReadExponentialGolomb(&golomb_ignored));
-  // chroma_qp_index_offset: se(v)
-  RETURN_FALSE_ON_FAIL(parser.ReadExponentialGolomb(&golomb_ignored));
-  // deblocking_filter_control_present_flag: u(1)
-  // constrained_intra_pred_flag: u(1)
-  RETURN_FALSE_ON_FAIL(parser.ReadBits(&bits_tmp, 2));
-  // redundant_pic_cnt_present_flag: u(1)
-  RETURN_FALSE_ON_FAIL(
-      parser.ReadBits(&pps_.redundant_pic_cnt_present_flag, 1));
-
-  pps_parsed_ = true;
-  return true;
-}
+H264BitstreamParser::H264BitstreamParser() {}
+H264BitstreamParser::~H264BitstreamParser() {}
 
 bool H264BitstreamParser::ParseNonParameterSetNalu(const uint8_t* source,
                                                    size_t source_length,
                                                    uint8_t nalu_type) {
-  RTC_CHECK(sps_parsed_);
-  RTC_CHECK(pps_parsed_);
-  last_slice_qp_delta_parsed_ = false;
-  std::unique_ptr<rtc::ByteBufferWriter> slice_rbsp(ParseRbsp(
-      source + kNaluHeaderAndTypeSize, source_length - kNaluHeaderAndTypeSize));
-  rtc::BitBuffer slice_reader(
-      reinterpret_cast<const uint8_t*>(slice_rbsp->Data()),
-      slice_rbsp->Length());
+  RTC_CHECK(sps_);
+  RTC_CHECK(pps_);
+  last_slice_qp_delta_ = rtc::Optional<int32_t>();
+  std::unique_ptr<rtc::Buffer> slice_rbsp(
+      H264::ParseRbsp(source, source_length));
+  rtc::BitBuffer slice_reader(slice_rbsp->data() + H264::kNaluTypeSize,
+                              slice_rbsp->size() - H264::kNaluTypeSize);
   // Check to see if this is an IDR slice, which has an extra field to parse
   // out.
-  bool is_idr = (source[kNaluHeaderSize] & 0x0F) == kNaluIdr;
-  uint8_t nal_ref_idc = (source[kNaluHeaderSize] & 0x60) >> 5;
+  bool is_idr = (source[0] & 0x0F) == H264::NaluType::kIdr;
+  uint8_t nal_ref_idc = (source[0] & 0x60) >> 5;
   uint32_t golomb_tmp;
   uint32_t bits_tmp;
 
@@ -340,16 +58,16 @@ bool H264BitstreamParser::ParseNonParameterSetNalu(const uint8_t* source,
   slice_type %= 5;
   // pic_parameter_set_id: ue(v)
   RETURN_FALSE_ON_FAIL(slice_reader.ReadExponentialGolomb(&golomb_tmp));
-  if (sps_.separate_colour_plane_flag == 1) {
+  if (sps_->separate_colour_plane_flag == 1) {
     // colour_plane_id
     RETURN_FALSE_ON_FAIL(slice_reader.ReadBits(&bits_tmp, 2));
   }
   // frame_num: u(v)
   // Represented by log2_max_frame_num_minus4 + 4 bits.
   RETURN_FALSE_ON_FAIL(
-      slice_reader.ReadBits(&bits_tmp, sps_.log2_max_frame_num_minus4 + 4));
+      slice_reader.ReadBits(&bits_tmp, sps_->log2_max_frame_num_minus4 + 4));
   uint32_t field_pic_flag = 0;
-  if (sps_.frame_mbs_only_flag == 0) {
+  if (sps_->frame_mbs_only_flag == 0) {
     // field_pic_flag: u(1)
     RETURN_FALSE_ON_FAIL(slice_reader.ReadBits(&field_pic_flag, 1));
     if (field_pic_flag != 0) {
@@ -363,45 +81,51 @@ bool H264BitstreamParser::ParseNonParameterSetNalu(const uint8_t* source,
   }
   // pic_order_cnt_lsb: u(v)
   // Represented by sps_.log2_max_pic_order_cnt_lsb_minus4 + 4 bits.
-  if (sps_.pic_order_cnt_type == 0) {
+  if (sps_->pic_order_cnt_type == 0) {
     RETURN_FALSE_ON_FAIL(slice_reader.ReadBits(
-        &bits_tmp, sps_.log2_max_pic_order_cnt_lsb_minus4 + 4));
-    if (pps_.bottom_field_pic_order_in_frame_present_flag &&
+        &bits_tmp, sps_->log2_max_pic_order_cnt_lsb_minus4 + 4));
+    if (pps_->bottom_field_pic_order_in_frame_present_flag &&
         field_pic_flag == 0) {
       // delta_pic_order_cnt_bottom: se(v)
       RETURN_FALSE_ON_FAIL(slice_reader.ReadExponentialGolomb(&golomb_tmp));
     }
   }
-  if (sps_.pic_order_cnt_type == 1 && !sps_.delta_pic_order_always_zero_flag) {
+  if (sps_->pic_order_cnt_type == 1 &&
+      !sps_->delta_pic_order_always_zero_flag) {
     // delta_pic_order_cnt[0]: se(v)
     RETURN_FALSE_ON_FAIL(slice_reader.ReadExponentialGolomb(&golomb_tmp));
-    if (pps_.bottom_field_pic_order_in_frame_present_flag && !field_pic_flag) {
+    if (pps_->bottom_field_pic_order_in_frame_present_flag && !field_pic_flag) {
       // delta_pic_order_cnt[1]: se(v)
       RETURN_FALSE_ON_FAIL(slice_reader.ReadExponentialGolomb(&golomb_tmp));
     }
   }
-  if (pps_.redundant_pic_cnt_present_flag) {
+  if (pps_->redundant_pic_cnt_present_flag) {
     // redundant_pic_cnt: ue(v)
     RETURN_FALSE_ON_FAIL(slice_reader.ReadExponentialGolomb(&golomb_tmp));
   }
-  if (slice_type == kSliceTypeB) {
+  if (slice_type == H264::SliceType::kB) {
     // direct_spatial_mv_pred_flag: u(1)
     RETURN_FALSE_ON_FAIL(slice_reader.ReadBits(&bits_tmp, 1));
   }
-  if (slice_type == kSliceTypeP || slice_type == kSliceTypeSp ||
-      slice_type == kSliceTypeB) {
-    uint32_t num_ref_idx_active_override_flag;
-    // num_ref_idx_active_override_flag: u(1)
-    RETURN_FALSE_ON_FAIL(
-        slice_reader.ReadBits(&num_ref_idx_active_override_flag, 1));
-    if (num_ref_idx_active_override_flag != 0) {
-      // num_ref_idx_l0_active_minus1: ue(v)
-      RETURN_FALSE_ON_FAIL(slice_reader.ReadExponentialGolomb(&golomb_tmp));
-      if (slice_type == kSliceTypeB) {
-        // num_ref_idx_l1_active_minus1: ue(v)
+  switch (slice_type) {
+    case H264::SliceType::kP:
+    case H264::SliceType::kB:
+    case H264::SliceType::kSp:
+      uint32_t num_ref_idx_active_override_flag;
+      // num_ref_idx_active_override_flag: u(1)
+      RETURN_FALSE_ON_FAIL(
+          slice_reader.ReadBits(&num_ref_idx_active_override_flag, 1));
+      if (num_ref_idx_active_override_flag != 0) {
+        // num_ref_idx_l0_active_minus1: ue(v)
         RETURN_FALSE_ON_FAIL(slice_reader.ReadExponentialGolomb(&golomb_tmp));
+        if (slice_type == H264::SliceType::kB) {
+          // num_ref_idx_l1_active_minus1: ue(v)
+          RETURN_FALSE_ON_FAIL(slice_reader.ReadExponentialGolomb(&golomb_tmp));
+        }
       }
-    }
+      break;
+    default:
+      break;
   }
   // assume nal_unit_type != 20 && nal_unit_type != 21:
   RTC_CHECK_NE(nalu_type, 20);
@@ -464,9 +188,10 @@ bool H264BitstreamParser::ParseNonParameterSetNalu(const uint8_t* source,
     }
   }
   // TODO(pbos): Do we need support for pred_weight_table()?
-  RTC_CHECK(!((pps_.weighted_pred_flag &&
-               (slice_type == kSliceTypeP || slice_type == kSliceTypeSp)) ||
-              (pps_.weighted_bipred_idc != 0 && slice_type == kSliceTypeB)))
+  RTC_CHECK(
+      !((pps_->weighted_pred_flag && (slice_type == H264::SliceType::kP ||
+                                      slice_type == H264::SliceType::kSp)) ||
+        (pps_->weighted_bipred_idc != 0 && slice_type == H264::SliceType::kB)))
       << "Missing support for pred_weight_table().";
   // if ((weighted_pred_flag && (slice_type == P || slice_type == SP)) ||
   //    (weighted_bipred_idc == 1 && slice_type == B)) {
@@ -518,23 +243,30 @@ bool H264BitstreamParser::ParseNonParameterSetNalu(const uint8_t* source,
   // cabac not supported: entropy_coding_mode_flag == 0 asserted above.
   // if (entropy_coding_mode_flag && slice_type != I && slice_type != SI)
   //   cabac_init_idc
+  int32_t last_slice_qp_delta;
   RETURN_FALSE_ON_FAIL(
-      slice_reader.ReadSignedExponentialGolomb(&last_slice_qp_delta_));
-  last_slice_qp_delta_parsed_ = true;
+      slice_reader.ReadSignedExponentialGolomb(&last_slice_qp_delta));
+  last_slice_qp_delta_ = rtc::Optional<int32_t>(last_slice_qp_delta);
   return true;
 }
 
 void H264BitstreamParser::ParseSlice(const uint8_t* slice, size_t length) {
-  uint8_t nalu_type = slice[4] & kNaluTypeMask;
+  H264::NaluType nalu_type = H264::ParseNaluType(slice[0]);
   switch (nalu_type) {
-    case kNaluSps:
-      RTC_CHECK(ParseSpsNalu(slice, length))
-          << "Failed to parse bitstream SPS.";
+    case H264::NaluType::kSps: {
+      sps_ = SpsParser::ParseSps(slice + H264::kNaluTypeSize,
+                                 length - H264::kNaluTypeSize);
+      if (!sps_)
+        FATAL() << "Unable to parse SPS from H264 bitstream.";
       break;
-    case kNaluPps:
-      RTC_CHECK(ParsePpsNalu(slice, length))
-          << "Failed to parse bitstream PPS.";
+    }
+    case H264::NaluType::kPps: {
+      pps_ = PpsParser::ParsePps(slice + H264::kNaluTypeSize,
+                                 length - H264::kNaluTypeSize);
+      if (!pps_)
+        FATAL() << "Unable to parse PPS from H264 bitstream.";
       break;
+    }
     default:
       RTC_CHECK(ParseNonParameterSetNalu(slice, length, nalu_type))
           << "Failed to parse picture slice.";
@@ -544,21 +276,17 @@ void H264BitstreamParser::ParseSlice(const uint8_t* slice, size_t length) {
 
 void H264BitstreamParser::ParseBitstream(const uint8_t* bitstream,
                                          size_t length) {
-  RTC_CHECK_GE(length, 4u);
-  std::vector<size_t> slice_markers = FindNaluStartSequences(bitstream, length);
-  RTC_CHECK(!slice_markers.empty());
-  for (size_t i = 0; i < slice_markers.size() - 1; ++i) {
-    ParseSlice(bitstream + slice_markers[i],
-               slice_markers[i + 1] - slice_markers[i]);
-  }
-  // Parse the last slice.
-  ParseSlice(bitstream + slice_markers.back(), length - slice_markers.back());
+  std::vector<H264::NaluIndex> nalu_indices =
+      H264::FindNaluIndices(bitstream, length);
+  RTC_CHECK(!nalu_indices.empty());
+  for (const H264::NaluIndex& index : nalu_indices)
+    ParseSlice(&bitstream[index.payload_start_offset], index.payload_size);
 }
 
 bool H264BitstreamParser::GetLastSliceQp(int* qp) const {
-  if (!last_slice_qp_delta_parsed_)
+  if (!last_slice_qp_delta_ || !pps_)
     return false;
-  *qp = 26 + pps_.pic_init_qp_minus26 + last_slice_qp_delta_;
+  *qp = 26 + pps_->pic_init_qp_minus26 + *last_slice_qp_delta_;
   return true;
 }