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, 11 insertions, 0 deletions

diff --git a/test/test_helpers.h b/test/test_helpers.h
new file mode 100644
index 0000000000..3dfe08fdbe
--- /dev/null
+++ b/test/test_helpers.h
@@ -0,0 +1,11 @@
+#ifndef MP_TESTS_H
+#define MP_TESTS_H
+
+#include <stdarg.h>
+#include <stddef.h>
+#include <setjmp.h>
+#include <cmocka.h>
+
+#include <stdio.h>
+
+#endif