avc_utils.cpp revision 6a63a939601645404fd98f58c19cc38ca818d99e 
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    if (profile_idc == 100 || profile_idc == 110
45            || profile_idc == 122 || profile_idc == 244
46            || profile_idc == 44 || profile_idc == 83 || profile_idc == 86) {
47        unsigned chroma_format_idc = parseUE(&br);
48        if (chroma_format_idc == 3) {
49            br.skipBits(1);  // residual_colour_transform_flag
50        }
51        parseUE(&br);  // bit_depth_luma_minus8
52        parseUE(&br);  // bit_depth_chroma_minus8
53        br.skipBits(1);  // qpprime_y_zero_transform_bypass_flag
54        CHECK_EQ(br.getBits(1), 0u);  // seq_scaling_matrix_present_flag
55    }
56
57    parseUE(&br);  // log2_max_frame_num_minus4
58    unsigned pic_order_cnt_type = parseUE(&br);
59
60    if (pic_order_cnt_type == 0) {
61        parseUE(&br);  // log2_max_pic_order_cnt_lsb_minus4
62    } else if (pic_order_cnt_type == 1) {
63        // offset_for_non_ref_pic, offset_for_top_to_bottom_field and
64        // offset_for_ref_frame are technically se(v), but since we are
65        // just skipping over them the midpoint does not matter.
66
67        br.getBits(1);  // delta_pic_order_always_zero_flag
68        parseUE(&br);  // offset_for_non_ref_pic
69        parseUE(&br);  // offset_for_top_to_bottom_field
70
71        unsigned num_ref_frames_in_pic_order_cnt_cycle = parseUE(&br);
72        for (unsigned i = 0; i < num_ref_frames_in_pic_order_cnt_cycle; ++i) {
73            parseUE(&br);  // offset_for_ref_frame
74        }
75    }
76
77    parseUE(&br);  // num_ref_frames
78    br.getBits(1);  // gaps_in_frame_num_value_allowed_flag
79
80    unsigned pic_width_in_mbs_minus1 = parseUE(&br);
81    unsigned pic_height_in_map_units_minus1 = parseUE(&br);
82    unsigned frame_mbs_only_flag = br.getBits(1);
83
84    *width = pic_width_in_mbs_minus1 * 16 + 16;
85
86    *height = (2 - frame_mbs_only_flag)
87        * (pic_height_in_map_units_minus1 * 16 + 16);
88}
89
90}  // namespace android
91
92