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 }