FFmpeg
mpeg12framerate.c
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1 /*
2  * This file is part of FFmpeg.
3  *
4  * FFmpeg 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  * FFmpeg 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 FFmpeg; 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 
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 
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++) {
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 }
AVRational av_div_q(AVRational b, AVRational c)
Divide one rational by another.
Definition: rational.c:88
Undefined Behavior In the C some operations are like signed integer dereferencing freed accessing outside allocated Undefined Behavior must not occur in a C it is not safe even if the output of undefined operations is unused The unsafety may seem nit picking but Optimizing compilers have in fact optimized code on the assumption that no undefined Behavior occurs Optimizing code based on wrong assumptions can and has in some cases lead to effects beyond the output of computations The signed integer overflow problem in speed critical code Code which is highly optimized and works with signed integers sometimes has the problem that often the output of the computation does not c
Definition: undefined.txt:32
static av_always_inline int cmp(MpegEncContext *s, const int x, const int y, const int subx, const int suby, const int size, const int h, int ref_index, int src_index, me_cmp_func cmp_func, me_cmp_func chroma_cmp_func, const int flags)
compares a block (either a full macroblock or a partition thereof) against a proposed motion-compensa...
Definition: motion_est.c:260
int n
Definition: avisynth_c.h:760
static void error(const char *err)
static void test(const char *pattern, const char *host)
Definition: noproxy.c:23
MPEG-1/2 tables.
Rational number (pair of numerator and denominator).
Definition: rational.h:58
and forward the test the status of outputs and forward it to the corresponding return FFERROR_NOT_READY If the filters stores internally one or a few frame for some it can consider them to be part of the FIFO and delay acknowledging a status change accordingly Example code
static int av_cmp_q(AVRational a, AVRational b)
Compare two rationals.
Definition: rational.h:89
Utilties for rational number calculation.
void ff_mpeg12_find_best_frame_rate(AVRational frame_rate, int *code, int *ext_n, int *ext_d, int nonstandard)
const AVRational ff_mpeg12_frame_rate_tab[16]
AVRational av_mul_q(AVRational b, AVRational c)
Multiply two rationals.
Definition: rational.c:80