H264 bitstream parser.

webrtc/modules/rtp_rtcp/source/h264_bitstream_parser.cc

+/*
+ *  Copyright (c) 2015 The WebRTC project authors. All Rights Reserved.
+ *
+ *  Use of this source code is governed by a BSD-style license
+ *  that can be found in the LICENSE file in the root of the source
+ *  tree. An additional intellectual property rights grant can be found
+ *  in the file PATENTS.  All contributing project authors may
+ *  be found in the AUTHORS file in the root of the source tree.
+ */
+#include "webrtc/modules/rtp_rtcp/source/h264_bitstream_parser.h"
+
+#include "webrtc/base/bitbuffer.h"
+#include "webrtc/base/bytebuffer.h"
+#include "webrtc/base/checks.h"
+#include "webrtc/base/logging.h"
+#include "webrtc/base/scoped_ptr.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 IDR type.
+static const uint8_t kNaluSps = 7;
+static const uint8_t kNaluPps = 8;
+static const uint8_t kNaluIdr = 0x5;
+static const uint8_t kNaluTypeMask = 0x1F;
+
+static const uint8_t kSliceTypeP = 0;
+static const uint8_t kSliceTypeB = 1;
+// static const uint8_t kSliceTypeI = 2;
+static const uint8_t kSliceTypeSp = 3;
+// static const uint8_t kSliceTypeSi = 4;
+}  // 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::ByteBuffer* ParseRbsp(const uint8_t* bytes, size_t length) {
+  // Copied from webrtc::H264SpsParser::Parse.
+  rtc::ByteBuffer* rbsp_buffer = new rtc::ByteBuffer;
+  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)) {                         \
+    LOG_F(LS_ERROR) << "FAILED: " #x; \
+    return false;                     \
+  }
+
+// 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) {
+  // Parse out the SPS RBSP. It should be small, so it's ok that we create a
+  // copy. We'll eventually write this back.
+  rtc::scoped_ptr<rtc::ByteBuffer> sps_rbsp(
+      ParseRbsp(sps + kNaluHeaderAndTypeSize, length - kNaluHeaderAndTypeSize));
+  rtc::BitBuffer sps_parser(reinterpret_cast<const uint8*>(sps_rbsp->Data()),
+                            sps_rbsp->Length());
+
+  uint8_t byte_tmp;
+  uint32_t golomb_tmp;
+  uint32_t bits_tmp;
+
+  // profile_idc: u(8).
+  uint8 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));
+  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 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(&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.
+      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(&log2_max_frame_num_minus4_));
+  // pic_order_cnt_type: ue(v)
+  RETURN_FALSE_ON_FAIL(
+      sps_parser.ReadExponentialGolomb(&pic_order_cnt_type_));
+
+  if (pic_order_cnt_type_ == 0) {
+    // log2_max_pic_order_cnt_lsb_minus4: ue(v)
+    RETURN_FALSE_ON_FAIL(
+        sps_parser.ReadExponentialGolomb(&log2_max_pic_order_cnt_lsb_minus4_));
+  } else if (pic_order_cnt_type_ == 1) {
+    // delta_pic_order_always_zero_flag: u(1)
+    RETURN_FALSE_ON_FAIL(
+        sps_parser.ReadBits(&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(&frame_mbs_only_flag_, 1));
+  return true;
+}
+
+bool H264BitstreamParser::ParsePpsNalu(const uint8_t* pps, size_t length) {
+  // We're starting a new stream, so reset picture type rewriting values.
+  rtc::scoped_ptr<rtc::ByteBuffer> buffer(
+      ParseRbsp(pps + kNaluHeaderAndTypeSize, length - kNaluHeaderAndTypeSize));
+  rtc::BitBuffer parser(reinterpret_cast<const uint8*>(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): Is this true when we don't need to rewrite alignment or is it
+  // trivial to parse?
+  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));
+  bottom_field_pic_order_in_frame_present_flag_ =
+      static_cast<bool>(bottom_field_pic_order_in_frame_present_flag);
+
+  // 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)
+  // weighted_bipred_idc: u(2)
+  RETURN_FALSE_ON_FAIL(parser.ReadBits(&bits_tmp, 3));
+
+  // pic_init_qp_minus26: se(v)
+  RETURN_FALSE_ON_FAIL(
+      parser.ReadSignedExponentialGolomb(&pic_init_qp_minus26_));
+  printf("pic_init_qp: %d\n", pic_init_qp_minus26_ + 26);
+  // 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)
+  RETURN_FALSE_ON_FAIL(parser.ReadBits(&bits_tmp, 1));
+  // constrained_intra_pred_flag: u(1)
+  RETURN_FALSE_ON_FAIL(parser.ReadBits(&bits_tmp, 1));
+  // redundant_pic_cnt_present_flag: u(1)
+  RETURN_FALSE_ON_FAIL(parser.ReadBits(&redundant_pic_cnt_present_flag_, 1));
+
+  return true;
+}
+
+bool H264BitstreamParser::ParseNonParameterSetNalu(const uint8_t* source,
+                                                   size_t source_length) {
+  rtc::scoped_ptr<rtc::ByteBuffer> slice_rbsp(ParseRbsp(
+      source + kNaluHeaderAndTypeSize, source_length - kNaluHeaderAndTypeSize));
+  rtc::BitBuffer slice_reader(
+      reinterpret_cast<const uint8*>(slice_rbsp->Data()), slice_rbsp->Length());
+  // 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;
+  uint32_t golomb_tmp;
+  uint32_t bits_tmp;
+
+  // first_mb_in_slice: ue(v)
+  RETURN_FALSE_ON_FAIL(slice_reader.ReadExponentialGolomb(&golomb_tmp));
+  // slice_type: ue(v)
+  uint32_t slice_type;
+  RETURN_FALSE_ON_FAIL(slice_reader.ReadExponentialGolomb(&slice_type));
+  // slice_type's 5..9 range is used to indicate things.that all slices of a
+  // picture have the same value of slice_type % 5, we don't care about that, so
+  // we map to the corresponding 0..4 range.
+  slice_type %= 5;
+  // pic_parameter_set_id: ue(v)
+  RETURN_FALSE_ON_FAIL(slice_reader.ReadExponentialGolomb(&golomb_tmp));
+  if (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, log2_max_frame_num_minus4_ + 4));
+  uint32 field_pic_flag = 0;
+  if (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) {
+      // bottom_field_flag: u(1)
+      RETURN_FALSE_ON_FAIL(slice_reader.ReadBits(&bits_tmp, 1));
+    }
+  }
+  if (is_idr) {
+    // idr_pic_id: ue(v)
+    RETURN_FALSE_ON_FAIL(slice_reader.ReadExponentialGolomb(&golomb_tmp));
+  }
+  // pic_order_cnt_lsb: u(v)

[noahric, 2015/09/03 17:48:58]

This needs to be behind a pic_order_cnt_type == 0 check (probably the cause of
the parser failure, since most streams in the wild will have pic_order_cnt_type
== 2).

[pbos-webrtc, 2015/09/04 10:01:20]

This gives me more reasonable values. Thanks a lot! :D

+  // Represented by log2_max_pic_order_cnt_lsb_minus4_ + 4 bits.
+  RETURN_FALSE_ON_FAIL(
+      slice_reader.ReadBits(&bits_tmp, log2_max_pic_order_cnt_lsb_minus4_ + 4));
+  if (bottom_field_pic_order_in_frame_present_flag_ && field_pic_flag == 0) {

[noahric, 2015/09/03 17:49:37]

(This is also part of pic_order_cnt_type == 0)

[pbos-webrtc, 2015/09/04 10:01:20]

Done.

+    // delta_pic_order_cnt_bottom: se(v)
+    RETURN_FALSE_ON_FAIL(slice_reader.ReadExponentialGolomb(&golomb_tmp));
+  }
+  if (pic_order_cnt_type_ == 1 && !delta_pic_order_always_zero_flag_) {
+    // delta_pic_order_cnt[0]: se(v)
+    RETURN_FALSE_ON_FAIL(slice_reader.ReadExponentialGolomb(&golomb_tmp));
+    if (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 (redundant_pic_cnt_present_flag_) {
+    // redundant_pic_cnt: ue(v)
+    RETURN_FALSE_ON_FAIL(slice_reader.ReadExponentialGolomb(&golomb_tmp));
+  }
+  if (slice_type == kSliceTypeB) {
+    // 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) {
+      // 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)
+        RETURN_FALSE_ON_FAIL(slice_reader.ReadExponentialGolomb(&golomb_tmp));
+      }
+    }
+  }
+  // assume nal_unit_type != 20 && nal_unit_type != 21:
+  // if (nal_unit_type == 20 || nal_unit_type == 21)
+  //   ref_pic_list_mvc_modification()
+  // else
+  {
+    // ref_pic_list_modification():
+    // |slice_type| checks here don't use named constants as they aren't named
+    // in the spec for this segment. Keeping them consistent makes it easier to
+    // verify that they are both the same.
+    if (slice_type % 5 != 2 && slice_type % 5 != 4) {
+      // ref_pic_list_modification_flag_l0: u(1)
+      uint32_t ref_pic_list_modification_flag_l0;
+      RETURN_FALSE_ON_FAIL(
+          slice_reader.ReadBits(&ref_pic_list_modification_flag_l0, 1));
+      if (ref_pic_list_modification_flag_l0) {
+        uint32_t modification_of_pic_nums_idc;
+        do {
+          // modification_of_pic_nums_idc: ue(v)
+          RETURN_FALSE_ON_FAIL(slice_reader.ReadExponentialGolomb(
+              &modification_of_pic_nums_idc));
+          if (modification_of_pic_nums_idc == 0 ||
+              modification_of_pic_nums_idc == 1) {
+            // abs_diff_pic_num_minus1: ue(v)
+            RETURN_FALSE_ON_FAIL(
+                slice_reader.ReadExponentialGolomb(&golomb_tmp));
+          } else if (modification_of_pic_nums_idc == 2) {
+            // long_term_pic_num: ue(v)
+            RETURN_FALSE_ON_FAIL(
+                slice_reader.ReadExponentialGolomb(&golomb_tmp));
+          }
+        } while (modification_of_pic_nums_idc != 3);
+      }
+    }
+    if (slice_type % 5 == 1) {
+      // ref_pic_list_modification_flag_l1: u(1)
+      uint32_t ref_pic_list_modification_flag_l1;
+      RETURN_FALSE_ON_FAIL(
+          slice_reader.ReadBits(&ref_pic_list_modification_flag_l1, 1));
+      if (ref_pic_list_modification_flag_l1) {
+        uint32_t modification_of_pic_nums_idc;
+        do {
+          // modification_of_pic_nums_idc: ue(v)
+          RETURN_FALSE_ON_FAIL(slice_reader.ReadExponentialGolomb(
+              &modification_of_pic_nums_idc));
+          if (modification_of_pic_nums_idc == 0 ||
+              modification_of_pic_nums_idc == 1) {
+            // abs_diff_pic_num_minus1: ue(v)
+            RETURN_FALSE_ON_FAIL(
+                slice_reader.ReadExponentialGolomb(&golomb_tmp));
+          } else if (modification_of_pic_nums_idc == 2) {
+            // long_term_pic_num: ue(v)
+            RETURN_FALSE_ON_FAIL(
+                slice_reader.ReadExponentialGolomb(&golomb_tmp));
+          }
+        } while (modification_of_pic_nums_idc != 3);
+      }
+    }
+  }
+  // TODO(pbos): Do we need support for pred_weight_table()?
+  // if ((weighted_pred_flag && (slice_type == P || slice_type == SP)) ||
+  //    (weighted_bipred_idc == 1 && slice_type == B)) {
+  //  pred_weight_table()
+  // }
+  if (nal_ref_idc) {
+    // dec_ref_pic_marking():
+    if (is_idr) {
+      // no_output_of_prior_pics_flag: u(1)
+      // long_term_reference_flag: u(1)
+      RETURN_FALSE_ON_FAIL(slice_reader.ReadBits(&bits_tmp, 2));
+    } else {
+      // adaptive_ref_pic_marking_mode_flag: u(1)
+      uint32_t adaptive_ref_pic_marking_mode_flag;
+      RETURN_FALSE_ON_FAIL(
+          slice_reader.ReadBits(&adaptive_ref_pic_marking_mode_flag, 1));
+      if (adaptive_ref_pic_marking_mode_flag) {
+        uint32_t memory_management_control_operation;
+        do {
+          // memory_management_control_operation: ue(v)
+          RETURN_FALSE_ON_FAIL(slice_reader.ReadExponentialGolomb(
+              &memory_management_control_operation));
+          if (memory_management_control_operation == 1 ||
+              memory_management_control_operation == 3) {
+            // difference_of_pic_nums_minus1: ue(v)
+            RETURN_FALSE_ON_FAIL(
+                slice_reader.ReadExponentialGolomb(&golomb_tmp));
+          }
+          if (memory_management_control_operation == 2) {
+            // long_term_pic_num: ue(v)
+            RETURN_FALSE_ON_FAIL(
+                slice_reader.ReadExponentialGolomb(&golomb_tmp));
+          }
+          if (memory_management_control_operation == 3 ||
+              memory_management_control_operation == 6) {
+            // long_term_frame_idx: ue(v)
+            RETURN_FALSE_ON_FAIL(
+                slice_reader.ReadExponentialGolomb(&golomb_tmp));
+          }
+          if (memory_management_control_operation == 4) {
+            // max_long_term_frame_idx_plus1: ue(v)
+            RETURN_FALSE_ON_FAIL(
+                slice_reader.ReadExponentialGolomb(&golomb_tmp));
+          }
+        } while (memory_management_control_operation != 0);
+      }
+    }
+  }
+  // cabac not supported: entropy_coding_mode_flag == 0 asserted above.
+  // if (entropy_coding_mode_flag && slice_type != I && slice_type != SI)
+  //   cabac_init_idc
+  RETURN_FALSE_ON_FAIL(
+      slice_reader.ReadSignedExponentialGolomb(&slice_qp_delta_));
+  printf("Slice QP: %d\n", GetLastSliceQp());
+  return true;
+}
+
+void H264BitstreamParser::ParseSlice(const uint8_t* slice, size_t length) {
+  printf("ParseSlice(%p, %zu): [%u..\n", slice, length, slice[4]);
+  uint8_t nalu_type = slice[4] & kNaluTypeMask;
+  switch (nalu_type) {
+    case kNaluSps:
+      CHECK(ParseSpsNalu(slice, length)) << "Failed to parse bitstream SPS.";
+      break;
+    case kNaluPps:
+      CHECK(ParsePpsNalu(slice, length)) << "Failed to parse bitstream PPS.";
+      break;
+    default:
+      CHECK(ParseNonParameterSetNalu(slice, length))
+          << "Failed to parse picture slice.";
+      break;
+  }
+}
+
+void H264BitstreamParser::ParseBitstream(const uint8_t* bitstream,
+                                         size_t length) {
+  assert(length >= 4);
+  // Skip first marker.
+  bitstream += 4;
+  length -= 4;
+  const uint8_t* head = bitstream;
+
+  // Set end buffer pointer to 4 bytes before actual buffer end so we can
+  // access head[1], head[2] and head[3] in a loop without buffer overrun.
+  const uint8_t* end = bitstream + length;
+
+  while (head < end - 4) {
+    if (head[0]) {

[noahric, 2015/09/03 17:48:58]

There's a much faster way to loop this (I did an experiment a few months ago to
find a fast/readable one):

  uint8_t* end = buffer + buffer_size - kNaluHeaderSize;
  for (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) {
      // THIS IS A NALU: head - buffer
      head += 4;
    } else {
      head++;
    }
  }
}

Or you could steal this version, which returns a vector of indices:
// Returns a vector of the NALU start sequences (0 0 0 1) in the given buffer.
std::vector<int> FindNaluStartSequences(const uint8_t* buffer,
                                        size_t buffer_size) {
  std::vector<int> 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(head - buffer);
      head += 4;
    } else {
      head++;
    }
  }

  return sequences;
}

+      head++;
+      continue;
+    }
+    if (head[1]) {  // got 00xx
+      head += 2;
+      continue;
+    }
+    if (head[2]) {  // got 0000xx
+      head += 3;
+      continue;
+    }
+    if (head[3] != 0x01) {  // got 000000xx
+      head++;               // xx != 1, continue searching.
+      continue;
+    }
+    size_t slice_length = head - bitstream + 4;
+    ParseSlice(bitstream - 4, slice_length);
+    // Skip separator.
+    head += 4;
+    bitstream = head;
+  }
+  // Parse the last slice.
+  ParseSlice(bitstream - 4, end - bitstream + 4);
+}
+
+int H264BitstreamParser::GetLastSliceQp() const {
+  return 26 + pic_init_qp_minus26_ + slice_qp_delta_;
+}
+
+}  // namespace webrtc