1 /*
2 * Copyright (c) 2016 The WebRTC project authors. All Rights Reserved.
3 *
4 * Use of this source code is governed by a BSD-style license
5 * that can be found in the LICENSE file in the root of the source
6 * tree. An additional intellectual property rights grant can be found
7 * in the file PATENTS. All contributing project authors may
8 * be found in the AUTHORS file in the root of the source tree.
9 */
10
11 #include "common_video/h264/sps_parser.h"
12
13 #include <memory>
14 #include <vector>
15
16 #include "common_video/h264/h264_common.h"
17 #include "rtc_base/bitbuffer.h"
18 #include "rtc_base/logging.h"
19
20 typedef rtc::Optional<webrtc::SpsParser::SpsState> OptionalSps;
21
22 #define RETURN_EMPTY_ON_FAIL(x) \
23 if (!(x)) { \
24 return OptionalSps(); \
25 }
26
27 namespace webrtc {
28
29 // General note: this is based off the 02/2014 version of the H.264 standard.
30 // You can find it on this page:
31 // http://www.itu.int/rec/T-REC-H.264
32
33 // Unpack RBSP and parse SPS state from the supplied buffer.
ParseSps(const uint8_t * data,size_t length)34 rtc::Optional<SpsParser::SpsState> SpsParser::ParseSps(const uint8_t* data,
35 size_t length) {
36 std::vector<uint8_t> unpacked_buffer = H264::ParseRbsp(data, length);
37 rtc::BitBuffer bit_buffer(unpacked_buffer.data(), unpacked_buffer.size());
38 return ParseSpsUpToVui(&bit_buffer);
39 }
40
ParseSpsUpToVui(rtc::BitBuffer * buffer)41 rtc::Optional<SpsParser::SpsState> SpsParser::ParseSpsUpToVui(
42 rtc::BitBuffer* buffer) {
43 // Now, we need to use a bit buffer to parse through the actual AVC SPS
44 // format. See Section 7.3.2.1.1 ("Sequence parameter set data syntax") of the
45 // H.264 standard for a complete description.
46 // Since we only care about resolution, we ignore the majority of fields, but
47 // we still have to actively parse through a lot of the data, since many of
48 // the fields have variable size.
49 // We're particularly interested in:
50 // chroma_format_idc -> affects crop units
51 // pic_{width,height}_* -> resolution of the frame in macroblocks (16x16).
52 // frame_crop_*_offset -> crop information
53
54 SpsState sps;
55
56 // The golomb values we have to read, not just consume.
57 uint32_t golomb_ignored;
58
59 // chroma_format_idc will be ChromaArrayType if separate_colour_plane_flag is
60 // 0. It defaults to 1, when not specified.
61 uint32_t chroma_format_idc = 1;
62
63 // profile_idc: u(8). We need it to determine if we need to read/skip chroma
64 // formats.
65 uint8_t profile_idc;
66 RETURN_EMPTY_ON_FAIL(buffer->ReadUInt8(&profile_idc));
67 // constraint_set0_flag through constraint_set5_flag + reserved_zero_2bits
68 // 1 bit each for the flags + 2 bits = 8 bits = 1 byte.
69 RETURN_EMPTY_ON_FAIL(buffer->ConsumeBytes(1));
70 // level_idc: u(8)
71 RETURN_EMPTY_ON_FAIL(buffer->ConsumeBytes(1));
72 // seq_parameter_set_id: ue(v)
73 RETURN_EMPTY_ON_FAIL(buffer->ReadExponentialGolomb(&sps.id));
74 sps.separate_colour_plane_flag = 0;
75 // See if profile_idc has chroma format information.
76 if (profile_idc == 100 || profile_idc == 110 || profile_idc == 122 ||
77 profile_idc == 244 || profile_idc == 44 || profile_idc == 83 ||
78 profile_idc == 86 || profile_idc == 118 || profile_idc == 128 ||
79 profile_idc == 138 || profile_idc == 139 || profile_idc == 134) {
80 // chroma_format_idc: ue(v)
81 RETURN_EMPTY_ON_FAIL(buffer->ReadExponentialGolomb(&chroma_format_idc));
82 if (chroma_format_idc == 3) {
83 // separate_colour_plane_flag: u(1)
84 RETURN_EMPTY_ON_FAIL(
85 buffer->ReadBits(&sps.separate_colour_plane_flag, 1));
86 }
87 // bit_depth_luma_minus8: ue(v)
88 RETURN_EMPTY_ON_FAIL(buffer->ReadExponentialGolomb(&golomb_ignored));
89 // bit_depth_chroma_minus8: ue(v)
90 RETURN_EMPTY_ON_FAIL(buffer->ReadExponentialGolomb(&golomb_ignored));
91 // qpprime_y_zero_transform_bypass_flag: u(1)
92 RETURN_EMPTY_ON_FAIL(buffer->ConsumeBits(1));
93 // seq_scaling_matrix_present_flag: u(1)
94 uint32_t seq_scaling_matrix_present_flag;
95 RETURN_EMPTY_ON_FAIL(buffer->ReadBits(&seq_scaling_matrix_present_flag, 1));
96 if (seq_scaling_matrix_present_flag) {
97 // Process the scaling lists just enough to be able to properly
98 // skip over them, so we can still read the resolution on streams
99 // where this is included.
100 int scaling_list_count = (chroma_format_idc == 3 ? 12 : 8);
101 for (int i = 0; i < scaling_list_count; ++i) {
102 // seq_scaling_list_present_flag[i] : u(1)
103 uint32_t seq_scaling_list_present_flags;
104 RETURN_EMPTY_ON_FAIL(
105 buffer->ReadBits(&seq_scaling_list_present_flags, 1));
106 if (seq_scaling_list_present_flags != 0) {
107 int last_scale = 8;
108 int next_scale = 8;
109 int size_of_scaling_list = i < 6 ? 16 : 64;
110 for (int j = 0; j < size_of_scaling_list; j++) {
111 if (next_scale != 0) {
112 int32_t delta_scale;
113 // delta_scale: se(v)
114 RETURN_EMPTY_ON_FAIL(
115 buffer->ReadSignedExponentialGolomb(&delta_scale));
116 next_scale = (last_scale + delta_scale + 256) % 256;
117 }
118 if (next_scale != 0)
119 last_scale = next_scale;
120 }
121 }
122 }
123 }
124 }
125 // log2_max_frame_num_minus4: ue(v)
126 RETURN_EMPTY_ON_FAIL(
127 buffer->ReadExponentialGolomb(&sps.log2_max_frame_num_minus4));
128 // pic_order_cnt_type: ue(v)
129 RETURN_EMPTY_ON_FAIL(buffer->ReadExponentialGolomb(&sps.pic_order_cnt_type));
130 if (sps.pic_order_cnt_type == 0) {
131 // log2_max_pic_order_cnt_lsb_minus4: ue(v)
132 RETURN_EMPTY_ON_FAIL(
133 buffer->ReadExponentialGolomb(&sps.log2_max_pic_order_cnt_lsb_minus4));
134 } else if (sps.pic_order_cnt_type == 1) {
135 // delta_pic_order_always_zero_flag: u(1)
136 RETURN_EMPTY_ON_FAIL(
137 buffer->ReadBits(&sps.delta_pic_order_always_zero_flag, 1));
138 // offset_for_non_ref_pic: se(v)
139 RETURN_EMPTY_ON_FAIL(buffer->ReadExponentialGolomb(&golomb_ignored));
140 // offset_for_top_to_bottom_field: se(v)
141 RETURN_EMPTY_ON_FAIL(buffer->ReadExponentialGolomb(&golomb_ignored));
142 // num_ref_frames_in_pic_order_cnt_cycle: ue(v)
143 uint32_t num_ref_frames_in_pic_order_cnt_cycle;
144 RETURN_EMPTY_ON_FAIL(
145 buffer->ReadExponentialGolomb(&num_ref_frames_in_pic_order_cnt_cycle));
146 for (size_t i = 0; i < num_ref_frames_in_pic_order_cnt_cycle; ++i) {
147 // offset_for_ref_frame[i]: se(v)
148 RETURN_EMPTY_ON_FAIL(buffer->ReadExponentialGolomb(&golomb_ignored));
149 }
150 }
151 // max_num_ref_frames: ue(v)
152 RETURN_EMPTY_ON_FAIL(buffer->ReadExponentialGolomb(&sps.max_num_ref_frames));
153 // gaps_in_frame_num_value_allowed_flag: u(1)
154 RETURN_EMPTY_ON_FAIL(buffer->ConsumeBits(1));
155 //
156 // IMPORTANT ONES! Now we're getting to resolution. First we read the pic
157 // width/height in macroblocks (16x16), which gives us the base resolution,
158 // and then we continue on until we hit the frame crop offsets, which are used
159 // to signify resolutions that aren't multiples of 16.
160 //
161 // pic_width_in_mbs_minus1: ue(v)
162 uint32_t pic_width_in_mbs_minus1;
163 RETURN_EMPTY_ON_FAIL(buffer->ReadExponentialGolomb(&pic_width_in_mbs_minus1));
164 // pic_height_in_map_units_minus1: ue(v)
165 uint32_t pic_height_in_map_units_minus1;
166 RETURN_EMPTY_ON_FAIL(
167 buffer->ReadExponentialGolomb(&pic_height_in_map_units_minus1));
168 // frame_mbs_only_flag: u(1)
169 RETURN_EMPTY_ON_FAIL(buffer->ReadBits(&sps.frame_mbs_only_flag, 1));
170 if (!sps.frame_mbs_only_flag) {
171 // mb_adaptive_frame_field_flag: u(1)
172 RETURN_EMPTY_ON_FAIL(buffer->ConsumeBits(1));
173 }
174 // direct_8x8_inference_flag: u(1)
175 RETURN_EMPTY_ON_FAIL(buffer->ConsumeBits(1));
176 //
177 // MORE IMPORTANT ONES! Now we're at the frame crop information.
178 //
179 // frame_cropping_flag: u(1)
180 uint32_t frame_cropping_flag;
181 uint32_t frame_crop_left_offset = 0;
182 uint32_t frame_crop_right_offset = 0;
183 uint32_t frame_crop_top_offset = 0;
184 uint32_t frame_crop_bottom_offset = 0;
185 RETURN_EMPTY_ON_FAIL(buffer->ReadBits(&frame_cropping_flag, 1));
186 if (frame_cropping_flag) {
187 // frame_crop_{left, right, top, bottom}_offset: ue(v)
188 RETURN_EMPTY_ON_FAIL(
189 buffer->ReadExponentialGolomb(&frame_crop_left_offset));
190 RETURN_EMPTY_ON_FAIL(
191 buffer->ReadExponentialGolomb(&frame_crop_right_offset));
192 RETURN_EMPTY_ON_FAIL(buffer->ReadExponentialGolomb(&frame_crop_top_offset));
193 RETURN_EMPTY_ON_FAIL(
194 buffer->ReadExponentialGolomb(&frame_crop_bottom_offset));
195 }
196 // vui_parameters_present_flag: u(1)
197 RETURN_EMPTY_ON_FAIL(buffer->ReadBits(&sps.vui_params_present, 1));
198
199 // Far enough! We don't use the rest of the SPS.
200
201 // Start with the resolution determined by the pic_width/pic_height fields.
202 sps.width = 16 * (pic_width_in_mbs_minus1 + 1);
203 sps.height =
204 16 * (2 - sps.frame_mbs_only_flag) * (pic_height_in_map_units_minus1 + 1);
205
206 // Figure out the crop units in pixels. That's based on the chroma format's
207 // sampling, which is indicated by chroma_format_idc.
208 if (sps.separate_colour_plane_flag || chroma_format_idc == 0) {
209 frame_crop_bottom_offset *= (2 - sps.frame_mbs_only_flag);
210 frame_crop_top_offset *= (2 - sps.frame_mbs_only_flag);
211 } else if (!sps.separate_colour_plane_flag && chroma_format_idc > 0) {
212 // Width multipliers for formats 1 (4:2:0) and 2 (4:2:2).
213 if (chroma_format_idc == 1 || chroma_format_idc == 2) {
214 frame_crop_left_offset *= 2;
215 frame_crop_right_offset *= 2;
216 }
217 // Height multipliers for format 1 (4:2:0).
218 if (chroma_format_idc == 1) {
219 frame_crop_top_offset *= 2;
220 frame_crop_bottom_offset *= 2;
221 }
222 }
223 // Subtract the crop for each dimension.
224 sps.width -= (frame_crop_left_offset + frame_crop_right_offset);
225 sps.height -= (frame_crop_top_offset + frame_crop_bottom_offset);
226
227 return OptionalSps(sps);
228 }
229
230 } // namespace webrtc
231