From afdc060bb3d2558130e48a76a0a342be034e294c Mon Sep 17 00:00:00 2001
From: wm4 <wm4@nowhere>
Date: Fri, 12 Jun 2015 19:23:46 +0200
Subject: chmap_sel: improve speaker replacement handling

This didn't really work since the last time the channel map fallback
code was touched. In some cases, quite bad results were selected.
---
 audio/chmap_sel.c | 50 +++++++++++++++++++++++++++++++++-----------------
 test/chmap_sel.c  | 15 +++++++++++++++
 2 files changed, 48 insertions(+), 17 deletions(-)

diff --git a/audio/chmap_sel.c b/audio/chmap_sel.c
index 855d0dc683..d1f6f2eee0 100644
--- a/audio/chmap_sel.c
+++ b/audio/chmap_sel.c
@@ -234,29 +234,45 @@ bool mp_chmap_sel_fallback(const struct mp_chmap_sel *s, struct mp_chmap *map)
         return true;
     }
 
-    struct mp_chmap best = {0};
+    struct mp_chmap best_of_best = {0};
+
+    for (int i = -1; i < (int)MP_ARRAY_SIZE(speaker_replacements); i++) {
+        struct mp_chmap best = {0};
+        struct mp_chmap t = *map;
+
+        if (i >= 0) {
+            struct mp_chmap *r = (struct mp_chmap *)speaker_replacements[i];
+            if (!replace_speakers(&t, r))
+                continue;
+        }
+
+        for (int n = 0; n < s->num_chmaps; n++) {
+            struct mp_chmap e = s->chmaps[n];
+
+            if (mp_chmap_is_unknown(&e))
+                continue;
 
-    for (int n = 0; n < s->num_chmaps; n++) {
-        struct mp_chmap e = s->chmaps[n];
-
-        if (mp_chmap_is_unknown(&e))
-            continue;
-
-        // in case we didn't match any fallback retry after replacing speakers
-        for (int i = -1; i < (int)MP_ARRAY_SIZE(speaker_replacements); i++) {
-            struct mp_chmap  t = *map;
-            if (i >= 0) {
-                struct mp_chmap *r = (struct mp_chmap *)speaker_replacements[i];
-                if (!replace_speakers(&t, r))
-                    continue;
-            }
             if (mp_chmap_is_better(&t, &best, &e))
                 best = e;
         }
+
+        if (best.num) {
+            if (best_of_best.num) {
+                // If best (without replacements) is not worse, but is actually
+                // better with replacements applied, pick it.
+                int bbest_lost = mp_chmap_diffn(map, &best_of_best);
+                int best_lost = mp_chmap_diffn(map, &best);
+                int repl_lost = mp_chmap_diffn(&t, &best);
+                if (best_lost <= bbest_lost && repl_lost < bbest_lost)
+                    best_of_best = best;
+            } else {
+                best_of_best = best;
+            }
+        }
     }
 
-    if (best.num) {
-        *map = best;
+    if (best_of_best.num) {
+        *map = best_of_best;
         return true;
     }
 
diff --git a/test/chmap_sel.c b/test/chmap_sel.c
index 914e00368f..928320058c 100644
--- a/test/chmap_sel.c
+++ b/test/chmap_sel.c
@@ -87,6 +87,20 @@ static void test_mp_chmap_sel_fallback_reject_unknown(void **state) {
     assert_string_equal(mp_chmap_to_str(&b), "5.1");
 }
 
+static void test_mp_chmap_sel_fallback_more_replacements(void **state) {
+    test_sel("quad", "quad(side)", LAYOUTS("quad(side)", "stereo"));
+    test_sel("quad", "7.0", LAYOUTS("quad(side)", "7.0"));
+    test_sel("quad", "7.0", LAYOUTS("7.0", "quad(side)"));
+    test_sel("quad", "7.1(wide-side)", LAYOUTS("7.1(wide-side)", "stereo"));
+    test_sel("quad", "7.1(wide-side)", LAYOUTS("stereo", "7.1(wide-side)"));
+    test_sel("quad", "fl-fr-fc-bl-br",
+             LAYOUTS("fl-fr-fc-bl-br", "fl-fr-sl-sr"));
+    test_sel("quad", "fl-fr-bl-br-na-na-na-na",
+             LAYOUTS("fl-fr-bl-br-na-na-na-na", "quad(side)", "stereo"));
+    test_sel("quad", "fl-fr-bl-br-na-na-na-na",
+             LAYOUTS("stereo", "quad(side)", "fl-fr-bl-br-na-na-na-na"));
+}
+
 int main(void) {
     const UnitTest tests[] = {
         unit_test(test_mp_chmap_sel_fallback_upmix),
@@ -101,6 +115,7 @@ int main(void) {
         unit_test(test_mp_chmap_sel_fallback_no_downmix),
         unit_test(test_mp_chmap_sel_fallback_minimal_downmix),
         unit_test(test_mp_chmap_sel_fallback_reject_unknown),
+        unit_test(test_mp_chmap_sel_fallback_more_replacements),
     };
     return run_tests(tests);
 }
-- 
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