Repo created

TMessagesProj/jni/voip/webrtc/common_video/h264/sps_parser.cc

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+/*
+ *  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 "common_video/h264/sps_parser.h"
+
+#include <cstdint>
+#include <vector>
+
+#include "common_video/h264/h264_common.h"
+#include "rtc_base/bitstream_reader.h"
+
+namespace {
+constexpr int kScalingDeltaMin = -128;
+constexpr int kScaldingDeltaMax = 127;
+}  // namespace
+
+namespace webrtc {
+
+SpsParser::SpsState::SpsState() = default;
+SpsParser::SpsState::SpsState(const SpsState&) = default;
+SpsParser::SpsState::~SpsState() = default;
+
+// 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
+
+// Unpack RBSP and parse SPS state from the supplied buffer.
+absl::optional<SpsParser::SpsState> SpsParser::ParseSps(const uint8_t* data,
+                                                        size_t length) {
+  std::vector<uint8_t> unpacked_buffer = H264::ParseRbsp(data, length);
+  BitstreamReader reader(unpacked_buffer);
+  return ParseSpsUpToVui(reader);
+}
+
+absl::optional<SpsParser::SpsState> SpsParser::ParseSpsUpToVui(
+    BitstreamReader& reader) {
+  // Now, we need to use a bitstream reader to parse through the actual AVC SPS
+  // format. See Section 7.3.2.1.1 ("Sequence parameter set data syntax") of the
+  // H.264 standard for a complete description.
+  // Since we only care about resolution, we ignore the majority of fields, but
+  // we still have to actively parse through a lot of the data, since many of
+  // the fields have variable size.
+  // We're particularly interested in:
+  // chroma_format_idc -> affects crop units
+  // pic_{width,height}_* -> resolution of the frame in macroblocks (16x16).
+  // frame_crop_*_offset -> crop information
+
+  SpsState sps;
+
+  // chroma_format_idc will be ChromaArrayType if separate_colour_plane_flag is
+  // 0. It defaults to 1, when not specified.
+  uint32_t chroma_format_idc = 1;
+
+  // profile_idc: u(8). We need it to determine if we need to read/skip chroma
+  // formats.
+  uint8_t profile_idc = reader.Read<uint8_t>();
+  // constraint_set0_flag through constraint_set5_flag + reserved_zero_2bits
+  // 1 bit each for the flags + 2 bits + 8 bits for level_idc = 16 bits.
+  reader.ConsumeBits(16);
+  // seq_parameter_set_id: ue(v)
+  sps.id = reader.ReadExponentialGolomb();
+  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)
+    chroma_format_idc = reader.ReadExponentialGolomb();
+    if (chroma_format_idc == 3) {
+      // separate_colour_plane_flag: u(1)
+      sps.separate_colour_plane_flag = reader.ReadBit();
+    }
+    // bit_depth_luma_minus8: ue(v)
+    reader.ReadExponentialGolomb();
+    // bit_depth_chroma_minus8: ue(v)
+    reader.ReadExponentialGolomb();
+    // qpprime_y_zero_transform_bypass_flag: u(1)
+    reader.ConsumeBits(1);
+    // seq_scaling_matrix_present_flag: u(1)
+    if (reader.Read<bool>()) {
+      // Process the scaling lists just enough to be able to properly
+      // skip over them, so we can still read the resolution on streams
+      // where this is included.
+      int scaling_list_count = (chroma_format_idc == 3 ? 12 : 8);
+      for (int i = 0; i < scaling_list_count; ++i) {
+        // seq_scaling_list_present_flag[i]  : u(1)
+        if (reader.Read<bool>()) {
+          int last_scale = 8;
+          int next_scale = 8;
+          int size_of_scaling_list = i < 6 ? 16 : 64;
+          for (int j = 0; j < size_of_scaling_list; j++) {
+            if (next_scale != 0) {
+              // delta_scale: se(v)
+              int delta_scale = reader.ReadSignedExponentialGolomb();
+              if (!reader.Ok() || delta_scale < kScalingDeltaMin ||
+                  delta_scale > kScaldingDeltaMax) {
+                return absl::nullopt;
+              }
+              next_scale = (last_scale + delta_scale + 256) % 256;
+            }
+            if (next_scale != 0)
+              last_scale = next_scale;
+          }
+        }
+      }
+    }
+  }
+  // log2_max_frame_num and log2_max_pic_order_cnt_lsb are used with
+  // BitstreamReader::ReadBits, which can read at most 64 bits at a time. We
+  // also have to avoid overflow when adding 4 to the on-wire golomb value,
+  // e.g., for evil input data, ReadExponentialGolomb might return 0xfffc.
+  const uint32_t kMaxLog2Minus4 = 12;
+
+  // log2_max_frame_num_minus4: ue(v)
+  uint32_t log2_max_frame_num_minus4 = reader.ReadExponentialGolomb();
+  if (!reader.Ok() || log2_max_frame_num_minus4 > kMaxLog2Minus4) {
+    return absl::nullopt;
+  }
+  sps.log2_max_frame_num = log2_max_frame_num_minus4 + 4;
+
+  // pic_order_cnt_type: ue(v)
+  sps.pic_order_cnt_type = reader.ReadExponentialGolomb();
+  if (sps.pic_order_cnt_type == 0) {
+    // log2_max_pic_order_cnt_lsb_minus4: ue(v)
+    uint32_t log2_max_pic_order_cnt_lsb_minus4 = reader.ReadExponentialGolomb();
+    if (!reader.Ok() || log2_max_pic_order_cnt_lsb_minus4 > kMaxLog2Minus4) {
+      return absl::nullopt;
+    }
+    sps.log2_max_pic_order_cnt_lsb = log2_max_pic_order_cnt_lsb_minus4 + 4;
+  } else if (sps.pic_order_cnt_type == 1) {
+    // delta_pic_order_always_zero_flag: u(1)
+    sps.delta_pic_order_always_zero_flag = reader.ReadBit();
+    // offset_for_non_ref_pic: se(v)
+    reader.ReadExponentialGolomb();
+    // offset_for_top_to_bottom_field: se(v)
+    reader.ReadExponentialGolomb();
+    // num_ref_frames_in_pic_order_cnt_cycle: ue(v)
+    uint32_t num_ref_frames_in_pic_order_cnt_cycle =
+        reader.ReadExponentialGolomb();
+    for (size_t i = 0; i < num_ref_frames_in_pic_order_cnt_cycle; ++i) {
+      // offset_for_ref_frame[i]: se(v)
+      reader.ReadExponentialGolomb();
+      if (!reader.Ok()) {
+        return absl::nullopt;
+      }
+    }
+  }
+  // max_num_ref_frames: ue(v)
+  sps.max_num_ref_frames = reader.ReadExponentialGolomb();
+  // gaps_in_frame_num_value_allowed_flag: u(1)
+  reader.ConsumeBits(1);
+  //
+  // IMPORTANT ONES! Now we're getting to resolution. First we read the pic
+  // width/height in macroblocks (16x16), which gives us the base resolution,
+  // and then we continue on until we hit the frame crop offsets, which are used
+  // to signify resolutions that aren't multiples of 16.
+  //
+  // pic_width_in_mbs_minus1: ue(v)
+  sps.width = 16 * (reader.ReadExponentialGolomb() + 1);
+  // pic_height_in_map_units_minus1: ue(v)
+  uint32_t pic_height_in_map_units_minus1 = reader.ReadExponentialGolomb();
+  // frame_mbs_only_flag: u(1)
+  sps.frame_mbs_only_flag = reader.ReadBit();
+  if (!sps.frame_mbs_only_flag) {
+    // mb_adaptive_frame_field_flag: u(1)
+    reader.ConsumeBits(1);
+  }
+  sps.height =
+      16 * (2 - sps.frame_mbs_only_flag) * (pic_height_in_map_units_minus1 + 1);
+  // direct_8x8_inference_flag: u(1)
+  reader.ConsumeBits(1);
+  //
+  // MORE IMPORTANT ONES! Now we're at the frame crop information.
+  //
+  uint32_t frame_crop_left_offset = 0;
+  uint32_t frame_crop_right_offset = 0;
+  uint32_t frame_crop_top_offset = 0;
+  uint32_t frame_crop_bottom_offset = 0;
+  // frame_cropping_flag: u(1)
+  if (reader.Read<bool>()) {
+    // frame_crop_{left, right, top, bottom}_offset: ue(v)
+    frame_crop_left_offset = reader.ReadExponentialGolomb();
+    frame_crop_right_offset = reader.ReadExponentialGolomb();
+    frame_crop_top_offset = reader.ReadExponentialGolomb();
+    frame_crop_bottom_offset = reader.ReadExponentialGolomb();
+  }
+  // vui_parameters_present_flag: u(1)
+  sps.vui_params_present = reader.ReadBit();
+
+  // Far enough! We don't use the rest of the SPS.
+  if (!reader.Ok()) {
+    return absl::nullopt;
+  }
+
+  // Figure out the crop units in pixels. That's based on the chroma format's
+  // sampling, which is indicated by chroma_format_idc.
+  if (sps.separate_colour_plane_flag || chroma_format_idc == 0) {
+    frame_crop_bottom_offset *= (2 - sps.frame_mbs_only_flag);
+    frame_crop_top_offset *= (2 - sps.frame_mbs_only_flag);
+  } else if (!sps.separate_colour_plane_flag && chroma_format_idc > 0) {
+    // Width multipliers for formats 1 (4:2:0) and 2 (4:2:2).
+    if (chroma_format_idc == 1 || chroma_format_idc == 2) {
+      frame_crop_left_offset *= 2;
+      frame_crop_right_offset *= 2;
+    }
+    // Height multipliers for format 1 (4:2:0).
+    if (chroma_format_idc == 1) {
+      frame_crop_top_offset *= 2;
+      frame_crop_bottom_offset *= 2;
+    }
+  }
+  // Subtract the crop for each dimension.
+  sps.width -= (frame_crop_left_offset + frame_crop_right_offset);
+  sps.height -= (frame_crop_top_offset + frame_crop_bottom_offset);
+
+  return sps;
+}
+
+}  // namespace webrtc