mpeg12: Move finding the best frame rate to common code

Previously in the mpeg2_metadata filter.  Also adds a test.

5 files changed, 161 insertions, 53 deletions

diff --git a/libavcodec/Makefile b/libavcodec/Makefile
index 9c485b222e..c750abd2d3 100644
--- a/libavcodec/Makefile
+++ b/libavcodec/Makefile
@@ -824,6 +824,7 @@ TESTPROGS-$(CONFIG_FFT)                   += fft fft-fixed
 TESTPROGS-$(CONFIG_GOLOMB)                += golomb
 TESTPROGS-$(CONFIG_IDCTDSP)               += dct
 TESTPROGS-$(CONFIG_IIRFILTER)             += iirfilter
+TESTPROGS-$(CONFIG_MPEGVIDEO)             += mpeg12framerate
 TESTPROGS-$(CONFIG_RANGECODER)            += rangecoder
 
 TESTOBJS = dctref.o
diff --git a/libavcodec/mpeg12.h b/libavcodec/mpeg12.h
index 17f0b781e6..26de7a48a8 100644
--- a/libavcodec/mpeg12.h
+++ b/libavcodec/mpeg12.h
@@ -64,4 +64,8 @@ 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 */
diff --git a/libavcodec/mpeg12framerate.c b/libavcodec/mpeg12framerate.c
index b11dd5e01d..acfef09745 100644
--- a/libavcodec/mpeg12framerate.c
+++ b/libavcodec/mpeg12framerate.c
@@ -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;
+    }
+}
diff --git a/libavcodec/mpeg2_metadata_bsf.c b/libavcodec/mpeg2_metadata_bsf.c
index 80e946f58e..5dae481d3d 100644
--- a/libavcodec/mpeg2_metadata_bsf.c
+++ b/libavcodec/mpeg2_metadata_bsf.c
@@ -23,6 +23,7 @@
 #include "bsf.h"
 #include "cbs.h"
 #include "cbs_mpeg2.h"
+#include "mpeg12.h"
 
 typedef struct MPEG2MetadataContext {
     const AVClass *class;
@@ -99,63 +100,14 @@ static int mpeg2_metadata_update_fragment(AVBSFContext *bsf,
     }
 
     if (ctx->frame_rate.num && ctx->frame_rate.den) {
-        // Table 6-4.
-        static AVRational frame_rate_table[] = {
-            { 0, 0 },
-            { 24000, 1001 },
-            { 24,    1    },
-            { 25,    1    },
-            { 30000, 1001 },
-            { 30,    1    },
-            { 50,    1    },
-            { 60000, 1001 },
-            { 60,    1    },
-        };
         int code, ext_n, ext_d;
-        AVRational best_error = { INT_MAX, 1 };
-
-        for (i = 1; i < FF_ARRAY_ELEMS(frame_rate_table); i++) {
-            if (av_cmp_q(ctx->frame_rate, frame_rate_table[i]) == 0) {
-                code  = i;
-                ext_n = 1;
-                ext_d = 1;
-                goto found_frame_rate;
-            }
-        }
 
-        for (i = 1; i < FF_ARRAY_ELEMS(frame_rate_table); i++) {
-            AVRational fr, error;
-            int n, d, cmp;
-            for (n = 1; n <= 4; n++) {
-                for (d = 1; d <= 32; d++) {
-                    fr = av_mul_q(frame_rate_table[i],
-                                  (AVRational) { n, d });
-                    cmp = av_cmp_q(fr, ctx->frame_rate);
-                    if (cmp == 0) {
-                        code  = i;
-                        ext_n = n;
-                        ext_d = d;
-                        goto found_frame_rate;
-                    }
-                    if (cmp < 0)
-                        error = av_div_q(ctx->frame_rate, fr);
-                    else
-                        error = av_div_q(fr, ctx->frame_rate);
-                    cmp = av_cmp_q(error, best_error);
-                    if (cmp < 0 || (cmp == 0 && n == 1 && d == 1)) {
-                        code  = i;
-                        ext_n = n;
-                        ext_d = d;
-                        best_error = error;
-                    }
-                }
-            }
-        }
+        ff_mpeg12_find_best_frame_rate(ctx->frame_rate,
+                                       &code, &ext_n, &ext_d, 0);
 
-    found_frame_rate:
         sh->frame_rate_code        = code;
-        se->frame_rate_extension_n = ext_n - 1;
-        se->frame_rate_extension_d = ext_d - 1;
+        se->frame_rate_extension_n = ext_n;
+        se->frame_rate_extension_d = ext_d;
     }
 
     if (ctx->video_format             >= 0 ||
diff --git a/libavcodec/tests/mpeg12framerate.c b/libavcodec/tests/mpeg12framerate.c
new file mode 100644
index 0000000000..c493cd0f5b
--- /dev/null
+++ b/libavcodec/tests/mpeg12framerate.c
@@ -0,0 +1,87 @@
+/*
+ * This file is part of Libav.
+ *
+ * Libav 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.
+ *
+ * Libav 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 Libav; 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;
+}