avc_utils.cpp revision 2d511ff0eb4c6127659795b642825c55879a15bc 
1/*
2 * Copyright (C) 2010 The Android Open Source Project
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 *      http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 */
16
17#include "include/avc_utils.h"
18
19#include <media/stagefright/foundation/ABitReader.h>
20#include <media/stagefright/foundation/ADebug.h>
21
22namespace android {
23
24unsigned parseUE(ABitReader *br) {
25    unsigned numZeroes = 0;
26    while (br->getBits(1) == 0) {
27        ++numZeroes;
28    }
29
30    unsigned x = br->getBits(numZeroes);
31
32    return x + (1u << numZeroes) - 1;
33}
34
35// Determine video dimensions from the sequence parameterset.
36void FindAVCDimensions(
37        const sp<ABuffer> &seqParamSet, int32_t *width, int32_t *height) {
38    ABitReader br(seqParamSet->data() + 1, seqParamSet->size() - 1);
39
40    unsigned profile_idc = br.getBits(8);
41    br.skipBits(16);
42    parseUE(&br);  // seq_parameter_set_id
43
44    unsigned chroma_format_idc = 1;  // 4:2:0 chroma format
45
46    if (profile_idc == 100 || profile_idc == 110
47            || profile_idc == 122 || profile_idc == 244
48            || profile_idc == 44 || profile_idc == 83 || profile_idc == 86) {
49        chroma_format_idc = parseUE(&br);
50        if (chroma_format_idc == 3) {
51            br.skipBits(1);  // residual_colour_transform_flag
52        }
53        parseUE(&br);  // bit_depth_luma_minus8
54        parseUE(&br);  // bit_depth_chroma_minus8
55        br.skipBits(1);  // qpprime_y_zero_transform_bypass_flag
56        CHECK_EQ(br.getBits(1), 0u);  // seq_scaling_matrix_present_flag
57    }
58
59    parseUE(&br);  // log2_max_frame_num_minus4
60    unsigned pic_order_cnt_type = parseUE(&br);
61
62    if (pic_order_cnt_type == 0) {
63        parseUE(&br);  // log2_max_pic_order_cnt_lsb_minus4
64    } else if (pic_order_cnt_type == 1) {
65        // offset_for_non_ref_pic, offset_for_top_to_bottom_field and
66        // offset_for_ref_frame are technically se(v), but since we are
67        // just skipping over them the midpoint does not matter.
68
69        br.getBits(1);  // delta_pic_order_always_zero_flag
70        parseUE(&br);  // offset_for_non_ref_pic
71        parseUE(&br);  // offset_for_top_to_bottom_field
72
73        unsigned num_ref_frames_in_pic_order_cnt_cycle = parseUE(&br);
74        for (unsigned i = 0; i < num_ref_frames_in_pic_order_cnt_cycle; ++i) {
75            parseUE(&br);  // offset_for_ref_frame
76        }
77    }
78
79    parseUE(&br);  // num_ref_frames
80    br.getBits(1);  // gaps_in_frame_num_value_allowed_flag
81
82    unsigned pic_width_in_mbs_minus1 = parseUE(&br);
83    unsigned pic_height_in_map_units_minus1 = parseUE(&br);
84    unsigned frame_mbs_only_flag = br.getBits(1);
85
86    *width = pic_width_in_mbs_minus1 * 16 + 16;
87
88    *height = (2 - frame_mbs_only_flag)
89        * (pic_height_in_map_units_minus1 * 16 + 16);
90
91    if (!frame_mbs_only_flag) {
92        br.getBits(1);  // mb_adaptive_frame_field_flag
93    }
94
95    br.getBits(1);  // direct_8x8_inference_flag
96
97    if (br.getBits(1)) {  // frame_cropping_flag
98        unsigned frame_crop_left_offset = parseUE(&br);
99        unsigned frame_crop_right_offset = parseUE(&br);
100        unsigned frame_crop_top_offset = parseUE(&br);
101        unsigned frame_crop_bottom_offset = parseUE(&br);
102
103        unsigned cropUnitX, cropUnitY;
104        if (chroma_format_idc == 0  /* monochrome */) {
105            cropUnitX = 1;
106            cropUnitY = 2 - frame_mbs_only_flag;
107        } else {
108            unsigned subWidthC = (chroma_format_idc == 3) ? 1 : 2;
109            unsigned subHeightC = (chroma_format_idc == 1) ? 2 : 1;
110
111            cropUnitX = subWidthC;
112            cropUnitY = subHeightC * (2 - frame_mbs_only_flag);
113        }
114
115        LOGV("frame_crop = (%u, %u, %u, %u), cropUnitX = %u, cropUnitY = %u",
116             frame_crop_left_offset, frame_crop_right_offset,
117             frame_crop_top_offset, frame_crop_bottom_offset,
118             cropUnitX, cropUnitY);
119
120        *width -=
121            (frame_crop_left_offset + frame_crop_right_offset) * cropUnitX;
122        *height -=
123            (frame_crop_top_offset + frame_crop_bottom_offset) * cropUnitY;
124    }
125}
126
127}  // namespace android
128
129