Add H264 bitstream rewriting to limit frame reordering marker in header

webrtc/modules/rtp_rtcp/source/h264/pps_parser.cc

+/*
+ *  Copyright (c) 2016 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/pps_parser.h"
+
+#include "webrtc/modules/rtp_rtcp/source/h264/h264_common.h"
+#include "webrtc/base/bitbuffer.h"
+#include "webrtc/base/buffer.h"
+#include "webrtc/base/logging.h"
+
+#define RETURN_FALSE_ON_FAIL(x)                  \
+  if (!(x)) {                                    \
+    return rtc::Optional<PpsParser::PpsState>(); \
+  }
+
+namespace webrtc {
+
+// General note: this is based off the 02/2014 version of the H.264 standard.
+// You can find it on this page:
+// http://www.itu.int/rec/T-REC-H.264
+
+rtc::Optional<PpsParser::PpsState> PpsParser::ParsePps(const uint8_t* data,
+                                                       size_t length) {
+  // First, parse out rbsp, which is basically the source buffer minus emulation
+  // bytes (the last byte of a 0x00 0x00 0x03 sequence). RBSP is defined in
+  // section 7.3.1 of the H.264 standard.
+  std::unique_ptr<rtc::Buffer> unpacked_buffer = H264::ParseRbsp(data, length);
+  rtc::BitBuffer bit_buffer(unpacked_buffer->data(), unpacked_buffer->size());
+  return ParseInternal(&bit_buffer);
+}
+
+rtc::Optional<PpsParser::PpsState> PpsParser::ParseInternal(
+    rtc::BitBuffer* bit_buffer) {
+  PpsState pps;
+
+  uint32_t bits_tmp;
+  uint32_t golomb_ignored;
+  // pic_parameter_set_id: ue(v)
+  RETURN_FALSE_ON_FAIL(bit_buffer->ReadExponentialGolomb(&golomb_ignored));
+  // seq_parameter_set_id: ue(v)
+  RETURN_FALSE_ON_FAIL(bit_buffer->ReadExponentialGolomb(&golomb_ignored));
+  // entropy_coding_mode_flag: u(1)
+  uint32_t entropy_coding_mode_flag;
+  RETURN_FALSE_ON_FAIL(bit_buffer->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(
+      bit_buffer->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(
+      bit_buffer->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(
+        bit_buffer->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(
+            bit_buffer->ReadExponentialGolomb(&golomb_ignored));
+      }
+    } else if (slice_group_map_type == 1) {
+      // TODO(sprang): Implement support for dispersed slice group map type.
+      // See 8.2.2.2 Specification for dispersed slice group map type.

[stefan-webrtc, 2016/05/26 18:08:13]

Could you comment on why this is needed, and what the impact of not supporting
it is?

[sprang_webrtc, 2016/05/27 13:12:22]

To be honest I have no idea :)
While refactoring I just noticed we missed an if-clause for one of the valid
values.
Noah, this was your code originally, can you comment?

+    } 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(
+            bit_buffer->ReadExponentialGolomb(&golomb_ignored));
+        // bottom_right[iGroup]: ue(v)
+        RETURN_FALSE_ON_FAIL(
+            bit_buffer->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(bit_buffer->ReadBits(&bits_tmp, 1));
+      // slice_group_change_rate_minus1: ue(v)
+      RETURN_FALSE_ON_FAIL(bit_buffer->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(
+          bit_buffer->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(
+            bit_buffer->ReadBits(&bits_tmp, slice_group_id_bits));
+      }
+    }
+  }
+  // num_ref_idx_l0_default_active_minus1: ue(v)
+  RETURN_FALSE_ON_FAIL(bit_buffer->ReadExponentialGolomb(&golomb_ignored));
+  // num_ref_idx_l1_default_active_minus1: ue(v)
+  RETURN_FALSE_ON_FAIL(bit_buffer->ReadExponentialGolomb(&golomb_ignored));
+  // weighted_pred_flag: u(1)
+  uint32_t weighted_pred_flag;
+  RETURN_FALSE_ON_FAIL(bit_buffer->ReadBits(&weighted_pred_flag, 1));
+  pps.weighted_pred_flag = weighted_pred_flag != 0;
+  // weighted_bipred_idc: u(2)
+  RETURN_FALSE_ON_FAIL(bit_buffer->ReadBits(&pps.weighted_bipred_idc, 2));
+
+  // pic_init_qp_minus26: se(v)
+  RETURN_FALSE_ON_FAIL(
+      bit_buffer->ReadSignedExponentialGolomb(&pps.pic_init_qp_minus26));
+  // pic_init_qs_minus26: se(v)
+  RETURN_FALSE_ON_FAIL(bit_buffer->ReadExponentialGolomb(&golomb_ignored));
+  // chroma_qp_index_offset: se(v)
+  RETURN_FALSE_ON_FAIL(bit_buffer->ReadExponentialGolomb(&golomb_ignored));
+  // deblocking_filter_control_present_flag: u(1)
+  // constrained_intra_pred_flag: u(1)
+  RETURN_FALSE_ON_FAIL(bit_buffer->ReadBits(&bits_tmp, 2));
+  // redundant_pic_cnt_present_flag: u(1)
+  RETURN_FALSE_ON_FAIL(
+      bit_buffer->ReadBits(&pps.redundant_pic_cnt_present_flag, 1));
+
+  return rtc::Optional<PpsParser::PpsState>(pps);
+}
+
+}  // namespace webrtc