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mpeg12: Add a common function to find the best frame rate

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This will be used later in both the mpeg2_metadata filter and the
VAAPI MPEG-2 encoder.  Also adds a unit test.

(cherry picked from commit b5859e0b04)
This commit is contained in:
Mark Thompson 2017-09-12 22:11:56 +01:00
parent 03f982bbca
commit 278c308cea
5 changed files with 161 additions and 0 deletions
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1
libavcodec/Makefile
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@ -1090,6 +1090,7 @@ TESTPROGS-$(CONFIG_GOLOMB) += golomb
TESTPROGS-$(CONFIG_IDCTDSP) += dct
TESTPROGS-$(CONFIG_IIRFILTER) += iirfilter
TESTPROGS-$(HAVE_MMX) += motion
TESTPROGS-$(CONFIG_MPEGVIDEO) += mpeg12framerate
TESTPROGS-$(CONFIG_RANGECODER) += rangecoder
TESTPROGS-$(CONFIG_SNOW_ENCODER) += snowenc

4
libavcodec/mpeg12.h
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@ -73,4 +73,8 @@ void ff_mpeg1_encode_mb(MpegEncContext *s, int16_t block[8][64],
void ff_mpeg1_encode_init(MpegEncContext *s);
void ff_mpeg1_encode_slice_header(MpegEncContext *s);
void ff_mpeg12_find_best_frame_rate(AVRational frame_rate,
int *code, int *ext_n, int *ext_d,
int nonstandard);
#endif /* AVCODEC_MPEG12_H */

64
libavcodec/mpeg12framerate.c
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@ -18,6 +18,9 @@
#include "libavutil/rational.h"
#include "mpeg12.h"
#include "mpeg12data.h"
const AVRational ff_mpeg12_frame_rate_tab[16] = {
{ 0, 0},
{24000, 1001},
@ -37,3 +40,64 @@ const AVRational ff_mpeg12_frame_rate_tab[16] = {
{ 15, 1},
{ 0, 0},
};
void ff_mpeg12_find_best_frame_rate(AVRational frame_rate,
int *code, int *ext_n, int *ext_d,
int nonstandard)
{
int mpeg2 = ext_n && ext_d;
int max_code = nonstandard ? 12 : 8;
int c, n, d, best_c, best_n, best_d;
AVRational best_error = { INT_MAX, 1 };
// Default to NTSC if the inputs make no sense.
best_c = 4;
best_n = best_d = 1;
for (c = 1; c <= max_code; c++) {
if (av_cmp_q(frame_rate, ff_mpeg12_frame_rate_tab[c]) == 0) {
best_c = c;
goto found;
}
}
for (c = 1; c <= max_code; c++) {
for (n = 1; n <= (mpeg2 ? 4 : 1); n++) {
for (d = 1; d <= (mpeg2 ? 32 : 1); d++) {
AVRational test, error;
int cmp;
test = av_mul_q(ff_mpeg12_frame_rate_tab[c],
(AVRational) { n, d });
cmp = av_cmp_q(test, frame_rate);
if (cmp == 0) {
best_c = c;
best_n = n;
best_d = d;
goto found;
}
if (cmp < 0)
error = av_div_q(frame_rate, test);
else
error = av_div_q(test, frame_rate);
cmp = av_cmp_q(error, best_error);
if (cmp < 0 || (cmp == 0 && n == 1 && d == 1)) {
best_c = c;
best_n = n;
best_d = d;
best_error = error;
}
}
}
}
found:
*code = best_c;
if (mpeg2) {
*ext_n = best_n - 1;
*ext_d = best_d - 1;
}
}

87
libavcodec/tests/mpeg12framerate.c Normal file
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@ -0,0 +1,87 @@
/*
* This file is part of FFmpeg.
*
* FFmpeg is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
* License as published by the Free Software Foundation; either
* version 2.1 of the License, or (at your option) any later version.
*
* FFmpeg is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with FFmpeg; if not, write to the Free Software
* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
*/
#include "libavcodec/mpeg12.h"
#include "libavcodec/mpeg12data.h"
int main(void)
{
int i;
#define TEST_MATCH(frame_rate, code, ext_n, ext_d) do { \
AVRational fr = frame_rate; \
int c, n, d; \
ff_mpeg12_find_best_frame_rate(fr, &c, &n, &d, 0); \
if (c != code || n != ext_n || d != ext_d) { \
av_log(NULL, AV_LOG_ERROR, "Failed to match %d/%d: " \
"code = %d, ext_n = %d, ext_d = %d.\n", \
fr.num, fr.den, c, n, d); \
return 1; \
} \
} while (0)
#define TEST_EXACT(frn, frd) do { \
AVRational fr = (AVRational) { frn, frd }; \
int c, n, d; \
ff_mpeg12_find_best_frame_rate(fr, &c, &n, &d, 0); \
if (av_cmp_q(fr, av_mul_q(ff_mpeg12_frame_rate_tab[c], \
(AVRational) { n + 1, d + 1 })) != 0) { \
av_log(NULL, AV_LOG_ERROR, "Failed to find exact %d/%d: " \
"code = %d, ext_n = %d, ext_d = %d.\n", \
fr.num, fr.den, c, n, d); \
return 1; \
} \
} while (0)
// Framerates in the table must be chosen exactly.
for (i = 1; i <= 8; i++)
TEST_MATCH(ff_mpeg12_frame_rate_tab[i], i, 0, 0);
// As should the same ones with small perturbations.
// (1/1000 used here to be smaller than half the difference
// between 24 and 24000/1001.)
for (i = 1; i <= 8; i++) {
TEST_MATCH(av_sub_q(ff_mpeg12_frame_rate_tab[i],
(AVRational) { 1, 1000 }), i, 0, 0);
TEST_MATCH(av_add_q(ff_mpeg12_frame_rate_tab[i],
(AVRational) { 1, 1000 }), i, 0, 0);
}
// Exactly constructable framerates should be exact. Note that some
// values can be made in multiple ways (e.g. 12 = 24 / 2 == 60 / 5),
// and there is no reason to favour any particular choice.
TEST_EXACT( 1, 1);
TEST_EXACT( 2, 1);
TEST_EXACT( 12, 1);
TEST_EXACT( 15000, 1001);
TEST_EXACT( 15, 1);
TEST_EXACT( 120, 1);
TEST_EXACT(120000, 1001);
TEST_EXACT( 200, 1);
TEST_EXACT( 240, 1);
// Values higher than 240 (the highest representable, as 60 * 4 / 1)
// should be mapped to 240.
for (i = 240; i < 1000; i += 10)
TEST_MATCH(((AVRational) { i, 1 }), 8, 3, 0);
// Values lower than 24000/32032 (the lowest representable, as
// 24000/1001 * 1 / 32) should be mapped to 24000/32032.
for (i = 74; i > 0; i--)
TEST_MATCH(((AVRational) { i, 100 }), 1, 0, 31);
return 0;
}

5
tests/fate/libavcodec.mak
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@ -45,6 +45,11 @@ FATE_LIBAVCODEC-$(CONFIG_IIRFILTER) += fate-iirfilter
fate-iirfilter: libavcodec/tests/iirfilter$(EXESUF)
fate-iirfilter: CMD = run libavcodec/tests/iirfilter
FATE_LIBAVCODEC-$(CONFIG_MPEGVIDEO) += fate-mpeg12framerate
fate-mpeg12framerate: libavcodec/tests/mpeg12framerate$(EXESUF)
fate-mpeg12framerate: CMD = run libavcodec/tests/mpeg12framerate
fate-mpeg12framerate: REF = /dev/null
FATE_LIBAVCODEC-yes += fate-libavcodec-options
fate-libavcodec-options: libavcodec/tests/options$(EXESUF)
fate-libavcodec-options: CMD = run libavcodec/tests/options