chmap_sel: add multichannel fallback heuristic

Instead of just failing during channel map selection, try to select a close
layout that makes most sense and upmix/downmix to that instead of failing AO
initialization. The heuristic is rather simple, and uses the following steps:

1) If mono is required always prefer stereo to a multichannel upmix.
2) Search for an upmix that is an exact superset of the required channel map.
3) Search for a downmix that is the exact subset of the required channel map.
4) Search for either an upmix or downmix that is the closest (minimum difference
   of channels) to the required channel map.

1 files changed, 56 insertions, 0 deletions

diff --git a/test/chmap.c b/test/chmap.c
new file mode 100644
index 0000000000..f0e8a1802d
--- /dev/null
+++ b/test/chmap.c
@@ -0,0 +1,56 @@
+#include "test_helpers.h"
+#include "audio/chmap.h"
+
+static void test_mp_chmap_diff(void **state) {
+    struct mp_chmap a;
+    struct mp_chmap b;
+    struct mp_chmap diff;
+
+    mp_chmap_from_str(&a, bstr0("3.1"));
+    mp_chmap_from_str(&b, bstr0("2.1"));
+
+    mp_chmap_diff(&a, &b, &diff);
+    assert_int_equal(diff.num, 1);
+    assert_int_equal(diff.speaker[0], MP_SPEAKER_ID_FC);
+
+    mp_chmap_from_str(&b, bstr0("6.1(back)"));
+    mp_chmap_diff(&a, &b, &diff);
+    assert_int_equal(diff.num, 0);
+
+    mp_chmap_diff(&b, &a, &diff);
+    assert_int_equal(diff.num, 3);
+    assert_int_equal(diff.speaker[0], MP_SPEAKER_ID_BL);
+    assert_int_equal(diff.speaker[1], MP_SPEAKER_ID_BR);
+    assert_int_equal(diff.speaker[2], MP_SPEAKER_ID_BC);
+}
+
+static void test_mp_chmap_contains_with_related_chmaps(void **state) {
+    struct mp_chmap a;
+    struct mp_chmap b;
+
+    mp_chmap_from_str(&a, bstr0("3.1"));
+    mp_chmap_from_str(&b, bstr0("2.1"));
+
+    assert_true(mp_chmap_contains(&a, &b));
+    assert_false(mp_chmap_contains(&b, &a));
+}
+
+static void test_mp_chmap_contains_with_unrelated_chmaps(void **state) {
+    struct mp_chmap a;
+    struct mp_chmap b;
+
+    mp_chmap_from_str(&a, bstr0("mono"));
+    mp_chmap_from_str(&b, bstr0("stereo"));
+
+    assert_false(mp_chmap_contains(&a, &b));
+    assert_false(mp_chmap_contains(&b, &a));
+}
+
+int main(void) {
+    const UnitTest tests[] = {
+        unit_test(test_mp_chmap_diff),
+        unit_test(test_mp_chmap_contains_with_related_chmaps),
+        unit_test(test_mp_chmap_contains_with_unrelated_chmaps),
+    };
+    return run_tests(tests);
+}