audio: add chmap utility function

(cherry picked from commit d32b71d52e9a45c141d2bd132189db68613ab0fb)

2 files changed, 10 insertions, 0 deletions

diff --git a/audio/chmap.c b/audio/chmap.c
index 1c40c66b0f..61ba8b0fa7 100644
--- a/audio/chmap.c
+++ b/audio/chmap.c
@@ -400,6 +400,7 @@ void mp_chmap_get_reorder(int src[MP_NUM_CHANNELS], const struct mp_chmap *from,
         assert(src[n] < 0 || (to->speaker[n] == from->speaker[src[n]]));
 }
 
+// Return channels that are only in a.
 // Performs the difference between a and b, and store it in diff. If b has
 // channels that do not appear in a, those will not appear in the difference.
 // To get to those the argument ordering in the function call has to be
@@ -413,6 +414,14 @@ void mp_chmap_diff(const struct mp_chmap *a, const struct mp_chmap *b,
     mp_chmap_from_lavc(diff, (a_mask ^ b_mask) & a_mask);
 }
 
+// Return the number of channels only in a.
+int mp_chmap_diffn(const struct mp_chmap *a, const struct mp_chmap *b)
+{
+    struct mp_chmap diff;
+    mp_chmap_diff(a, b, &diff);
+    return diff.num;
+}
+
 // Checks whether a contains all the speakers in b
 bool mp_chmap_contains(const struct mp_chmap *a, const struct mp_chmap *b)
 {
diff --git a/audio/chmap.h b/audio/chmap.h
index 296b2a1712..7165375e46 100644
--- a/audio/chmap.h
+++ b/audio/chmap.h
@@ -128,6 +128,7 @@ void mp_chmap_get_reorder(int src[MP_NUM_CHANNELS], const struct mp_chmap *from,
 
 void mp_chmap_diff(const struct mp_chmap *a, const struct mp_chmap *b,
                    struct mp_chmap *diff);
+int mp_chmap_diffn(const struct mp_chmap *a, const struct mp_chmap *b);
 
 bool mp_chmap_contains(const struct mp_chmap *a, const struct mp_chmap *b);