mpeg12: Move finding the best frame rate to common code
[libav.git] / libavcodec / mpeg12framerate.c
1 /*
2 * This file is part of Libav.
3 *
4 * Libav is free software; you can redistribute it and/or
5 * modify it under the terms of the GNU Lesser General Public
6 * License as published by the Free Software Foundation; either
7 * version 2.1 of the License, or (at your option) any later version.
8 *
9 * Libav is distributed in the hope that it will be useful,
10 * but WITHOUT ANY WARRANTY; without even the implied warranty of
11 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
12 * Lesser General Public License for more details.
13 *
14 * You should have received a copy of the GNU Lesser General Public
15 * License along with Libav; if not, write to the Free Software
16 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
17 */
18
19 #include "libavutil/rational.h"
20
21 #include "mpeg12.h"
22 #include "mpeg12data.h"
23
24 const AVRational ff_mpeg12_frame_rate_tab[16] = {
25 { 0, 0},
26 {24000, 1001},
27 { 24, 1},
28 { 25, 1},
29 {30000, 1001},
30 { 30, 1},
31 { 50, 1},
32 {60000, 1001},
33 { 60, 1},
34 // Xing's 15fps: (9)
35 { 15, 1},
36 // libmpeg3's "Unofficial economy rates": (10-13)
37 { 5, 1},
38 { 10, 1},
39 { 12, 1},
40 { 15, 1},
41 { 0, 0},
42 };
43
44 void ff_mpeg12_find_best_frame_rate(AVRational frame_rate,
45 int *code, int *ext_n, int *ext_d,
46 int nonstandard)
47 {
48 int mpeg2 = ext_n && ext_d;
49 int max_code = nonstandard ? 12 : 8;
50 int c, n, d, best_c, best_n, best_d;
51 AVRational best_error = { INT_MAX, 1 };
52
53 // Default to NTSC if the inputs make no sense.
54 best_c = 4;
55 best_n = best_d = 1;
56
57 for (c = 1; c <= max_code; c++) {
58 if (av_cmp_q(frame_rate, ff_mpeg12_frame_rate_tab[c]) == 0) {
59 best_c = c;
60 goto found;
61 }
62 }
63
64 for (c = 1; c <= max_code; c++) {
65 for (n = 1; n <= (mpeg2 ? 4 : 1); n++) {
66 for (d = 1; d <= (mpeg2 ? 32 : 1); d++) {
67 AVRational test, error;
68 int cmp;
69
70 test = av_mul_q(ff_mpeg12_frame_rate_tab[c],
71 (AVRational) { n, d });
72
73 cmp = av_cmp_q(test, frame_rate);
74 if (cmp == 0) {
75 best_c = c;
76 best_n = n;
77 best_d = d;
78 goto found;
79 }
80
81 if (cmp < 0)
82 error = av_div_q(frame_rate, test);
83 else
84 error = av_div_q(test, frame_rate);
85
86 cmp = av_cmp_q(error, best_error);
87 if (cmp < 0 || (cmp == 0 && n == 1 && d == 1)) {
88 best_c = c;
89 best_n = n;
90 best_d = d;
91 best_error = error;
92 }
93 }
94 }
95 }
96
97 found:
98 *code = best_c;
99 if (mpeg2) {
100 *ext_n = best_n - 1;
101 *ext_d = best_d - 1;
102 }
103 }