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/*
* 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_sps_parser.h"
#include "webrtc/base/bytebuffer.h"
#include "webrtc/base/bitbuffer.h"
#include "webrtc/system_wrappers/interface/logging.h"
#define RETURN_FALSE_ON_FAIL(x) \
if (!(x)) { \
return false; \
}
namespace webrtc {
H264SpsParser::H264SpsParser(const uint8* sps, size_t byte_length)
: sps_(sps), byte_length_(byte_length), width_(), height_() {
}
bool H264SpsParser::Parse() {
// 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
const char* sps_bytes = reinterpret_cast<const char*>(sps_);
// 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.
rtc::ByteBuffer rbsp_buffer;
for (size_t i = 0; i < byte_length_;) {
if (i < byte_length_ - 3 &&
sps_[i] == 0 && sps_[i + 1] == 0 && sps_[i + 2] == 3) {
// Two rbsp bytes + the emulation byte.
rbsp_buffer.WriteBytes(sps_bytes + i, 2);
i += 3;
} else {
// Single rbsp byte.
rbsp_buffer.WriteBytes(sps_bytes + i, 1);
i++;
}
}
// Now, we need to use a bit buffer 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
rtc::BitBuffer parser(reinterpret_cast<const uint8*>(rbsp_buffer.Data()),
rbsp_buffer.Length());
// The golomb values we have to read, not just consume.
uint32 golomb_ignored;
// separate_colour_plane_flag is optional (assumed 0), but has implications
// about the ChromaArrayType, which modifies how we treat crop coordinates.
uint32 separate_colour_plane_flag = 0;
// chroma_format_idc will be ChromaArrayType if separate_colour_plane_flag is
// 0. It defaults to 1, when not specified.
uint32 chroma_format_idc = 1;
// profile_idc: u(8). We need it to determine if we need to read/skip chroma
// formats.
uint8 profile_idc;
RETURN_FALSE_ON_FAIL(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(parser.ConsumeBytes(1));
// level_idc: u(8)
RETURN_FALSE_ON_FAIL(parser.ConsumeBytes(1));
// seq_parameter_set_id: ue(v)
RETURN_FALSE_ON_FAIL(parser.ReadExponentialGolomb(&golomb_ignored));
// 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)
RETURN_FALSE_ON_FAIL(parser.ReadExponentialGolomb(&chroma_format_idc));
if (chroma_format_idc == 3) {
// separate_colour_plane_flag: u(1)
RETURN_FALSE_ON_FAIL(parser.ReadBits(&separate_colour_plane_flag, 1));
}
// bit_depth_luma_minus8: ue(v)
RETURN_FALSE_ON_FAIL(parser.ReadExponentialGolomb(&golomb_ignored));
// bit_depth_chroma_minus8: ue(v)
RETURN_FALSE_ON_FAIL(parser.ReadExponentialGolomb(&golomb_ignored));
// qpprime_y_zero_transform_bypass_flag: u(1)
RETURN_FALSE_ON_FAIL(parser.ConsumeBits(1));
// seq_scaling_matrix_present_flag: u(1)
uint32 seq_scaling_matrix_present_flag;
RETURN_FALSE_ON_FAIL(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 seq_scaling_list_present_flags;
if (chroma_format_idc != 3) {
RETURN_FALSE_ON_FAIL(
parser.ReadBits(&seq_scaling_list_present_flags, 8));
} else {
RETURN_FALSE_ON_FAIL(
parser.ReadBits(&seq_scaling_list_present_flags, 12));
}
// We don't support reading the sequence scaling list, and we don't really
// see/use them in practice, so we'll just reject the full sps if we see
// any provided.
if (seq_scaling_list_present_flags > 0) {
LOG(LS_WARNING) << "SPS contains scaling lists, which are unsupported.";
return false;
}
}
}
// log2_max_frame_num_minus4: ue(v)
RETURN_FALSE_ON_FAIL(parser.ReadExponentialGolomb(&golomb_ignored));
// pic_order_cnt_type: ue(v)
uint32 pic_order_cnt_type;
RETURN_FALSE_ON_FAIL(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(parser.ReadExponentialGolomb(&golomb_ignored));
} else if (pic_order_cnt_type == 1) {
// delta_pic_order_always_zero_flag: u(1)
RETURN_FALSE_ON_FAIL(parser.ConsumeBits(1));
// offset_for_non_ref_pic: se(v)
RETURN_FALSE_ON_FAIL(parser.ReadExponentialGolomb(&golomb_ignored));
// offset_for_top_to_bottom_field: se(v)
RETURN_FALSE_ON_FAIL(parser.ReadExponentialGolomb(&golomb_ignored));
// num_ref_frames_in_pic_order_cnt_cycle: ue(v)
uint32 num_ref_frames_in_pic_order_cnt_cycle;
RETURN_FALSE_ON_FAIL(
parser.ReadExponentialGolomb(&num_ref_frames_in_pic_order_cnt_cycle));
for (size_t i = 0; i < num_ref_frames_in_pic_order_cnt_cycle; ++i) {
// offset_for_ref_frame[i]: se(v)
RETURN_FALSE_ON_FAIL(parser.ReadExponentialGolomb(&golomb_ignored));
}
}
// max_num_ref_frames: ue(v)
RETURN_FALSE_ON_FAIL(parser.ReadExponentialGolomb(&golomb_ignored));
// gaps_in_frame_num_value_allowed_flag: u(1)
RETURN_FALSE_ON_FAIL(parser.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)
uint32 pic_width_in_mbs_minus1;
RETURN_FALSE_ON_FAIL(parser.ReadExponentialGolomb(&pic_width_in_mbs_minus1));
// pic_height_in_map_units_minus1: ue(v)
uint32 pic_height_in_map_units_minus1;
RETURN_FALSE_ON_FAIL(
parser.ReadExponentialGolomb(&pic_height_in_map_units_minus1));
// frame_mbs_only_flag: u(1)
uint32 frame_mbs_only_flag;
RETURN_FALSE_ON_FAIL(parser.ReadBits(&frame_mbs_only_flag, 1));
if (!frame_mbs_only_flag) {
// mb_adaptive_frame_field_flag: u(1)
RETURN_FALSE_ON_FAIL(parser.ConsumeBits(1));
}
// direct_8x8_inference_flag: u(1)
RETURN_FALSE_ON_FAIL(parser.ConsumeBits(1));
//
// MORE IMPORTANT ONES! Now we're at the frame crop information.
//
// frame_cropping_flag: u(1)
uint32 frame_cropping_flag;
uint32 frame_crop_left_offset = 0;
uint32 frame_crop_right_offset = 0;
uint32 frame_crop_top_offset = 0;
uint32 frame_crop_bottom_offset = 0;
RETURN_FALSE_ON_FAIL(parser.ReadBits(&frame_cropping_flag, 1));
if (frame_cropping_flag) {
// frame_crop_{left, right, top, bottom}_offset: ue(v)
RETURN_FALSE_ON_FAIL(parser.ReadExponentialGolomb(&frame_crop_left_offset));
RETURN_FALSE_ON_FAIL(
parser.ReadExponentialGolomb(&frame_crop_right_offset));
RETURN_FALSE_ON_FAIL(parser.ReadExponentialGolomb(&frame_crop_top_offset));
RETURN_FALSE_ON_FAIL(
parser.ReadExponentialGolomb(&frame_crop_bottom_offset));
}
// Far enough! We don't use the rest of the SPS.
// Start with the resolution determined by the pic_width/pic_height fields.
int width = 16 * (pic_width_in_mbs_minus1 + 1);
int height =
16 * (2 - frame_mbs_only_flag) * (pic_height_in_map_units_minus1 + 1);
// Figure out the crop units in pixels. That's based on the chroma format's
// sampling, which is indicated by chroma_format_idc.
if (separate_colour_plane_flag || chroma_format_idc == 0) {
frame_crop_bottom_offset *= (2 - frame_mbs_only_flag);
frame_crop_top_offset *= (2 - frame_mbs_only_flag);
} else if (!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.
width -= (frame_crop_left_offset + frame_crop_right_offset);
height -= (frame_crop_top_offset + frame_crop_bottom_offset);
width_ = width;
height_ = height;
return true;
}
} // namespace webrtc
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