diff --git a/Makefile b/Makefile
index 160d180188..34d79d638b 100644
--- a/Makefile
+++ b/Makefile
@@ -124,6 +124,7 @@ endif
 SOURCES = talloc.c \
           audio/audio.c \
           audio/chmap.c \
+          audio/chmap_sel.c \
           audio/fmt-conversion.c \
           audio/format.c \
           audio/mixer.c \
diff --git a/audio/audio.c b/audio/audio.c
index 8af6a20a1f..c9d5c9231c 100644
--- a/audio/audio.c
+++ b/audio/audio.c
@@ -37,8 +37,7 @@ void mp_audio_set_num_channels(struct mp_audio *mpa, int num_channels)
 void mp_audio_set_channels_old(struct mp_audio *mpa, int num_channels)
 {
     struct mp_chmap map;
-    mp_chmap_from_channels(&map, num_channels);
-    mp_chmap_reorder_to_alsa(&map);
+    mp_chmap_from_channels_alsa(&map, num_channels);
     mp_audio_set_channels(mpa, &map);
 }
 
diff --git a/audio/chmap.c b/audio/chmap.c
index 61df408e02..fcdb95edb3 100644
--- a/audio/chmap.c
+++ b/audio/chmap.c
@@ -100,6 +100,17 @@ static const struct mp_chmap default_layouts[MP_NUM_CHANNELS + 1] = {
     MP_CHMAP8(FL, FR, FC, LFE, BL, BR, SL, SR), // 7.1
 };
 
+// The channel order was lavc/waveex, but differs from lavc for 5, 6 and 8
+// channels. 3 and 7 channels were likely undefined (no ALSA support).
+static const char *mplayer_layouts[MP_NUM_CHANNELS + 1] = {
+    [1] = "mono",
+    [2] = "stereo",
+    [4] = "4.0",
+    [5] = "5.0(alsa)",
+    [6] = "5.1(alsa)",
+    [8] = "7.1(alsa)",
+};
+
 // Returns true if speakers are mapped uniquely, and there's at least 1 channel.
 bool mp_chmap_is_valid(const struct mp_chmap *src)
 {
@@ -192,6 +203,19 @@ void mp_chmap_from_channels(struct mp_chmap *dst, int num_channels)
     }
 }
 
+// Try to do what mplayer/mplayer2/mpv did before channel layouts were
+// introduced, i.e. get the old default channel order.
+void mp_chmap_from_channels_alsa(struct mp_chmap *dst, int num_channels)
+{
+    if (num_channels < 0 || num_channels > MP_NUM_CHANNELS) {
+        *dst = (struct mp_chmap) {0};
+    } else {
+        mp_chmap_from_str(dst, bstr0(mplayer_layouts[num_channels]));
+        if (!dst->num)
+            mp_chmap_from_channels(dst, num_channels);
+    }
+}
+
 // Set *dst to an unknown layout for the given numbers of channels.
 // If the number of channels is invalid, an invalid map is set, and
 // mp_chmap_is_valid(dst) will return false.
@@ -314,22 +338,6 @@ void mp_chmap_reorder_to_lavc(struct mp_chmap *map)
     mp_chmap_from_lavc(map, mask);
 }
 
-// Try to do what mplayer/mplayer2/mpv did before channel layouts were
-// introduced, i.e. get the old default channel order.
-void mp_chmap_reorder_to_alsa(struct mp_chmap *map)
-{
-    // The channel order was lavc/waveex, but differs from lavc for 5, 6 and 8
-    // channels. 3 and 7 channels were likely undefined (no ALSA support).
-    mp_chmap_from_channels(map, map->num);
-    if (map->num == 5) {
-        mp_chmap_from_str(map, bstr0("5.0(alsa)"));
-    } else if (map->num == 6) {
-        mp_chmap_from_str(map, bstr0("5.1(alsa)"));
-    } else if (map->num == 8) {
-        mp_chmap_from_str(map, bstr0("7.1(alsa)"));
-    }
-}
-
 // Get reordering array for from->to reordering. from->to must have the same set
 // of speakers (i.e. same number and speaker IDs, just different order). Then,
 // for each speaker n, dst[n] will be set such that:
diff --git a/audio/chmap.h b/audio/chmap.h
index 9ab97ac8ba..929283dfd5 100644
--- a/audio/chmap.h
+++ b/audio/chmap.h
@@ -104,6 +104,7 @@ void mp_chmap_reorder_norm(struct mp_chmap *map);
 
 void mp_chmap_from_channels(struct mp_chmap *dst, int num_channels);
 void mp_chmap_set_unknown(struct mp_chmap *dst, int num_channels);
+void mp_chmap_from_channels_alsa(struct mp_chmap *dst, int num_channels);
 
 void mp_chmap_remove_useless_channels(struct mp_chmap *map,
                                       const struct mp_chmap *requested);
@@ -115,8 +116,6 @@ void mp_chmap_from_lavc(struct mp_chmap *dst, uint64_t src);
 bool mp_chmap_is_lavc(const struct mp_chmap *src);
 void mp_chmap_reorder_to_lavc(struct mp_chmap *map);
 
-void mp_chmap_reorder_to_alsa(struct mp_chmap *map);
-
 void mp_chmap_get_reorder(int dst[MP_NUM_CHANNELS], const struct mp_chmap *from,
                           const struct mp_chmap *to);
 
@@ -130,4 +129,6 @@ void mp_chmap_print_help(int msgt, int msgl);
 #define mp_chmap_is_waveext mp_chmap_is_lavc
 #define mp_chmap_reorder_to_waveext mp_chmap_reorder_to_lavc
 
+#define mp_chmap_reorder_to_alsa(x) mp_chmap_from_channels_alsa((x), (x)->num)
+
 #endif
diff --git a/audio/chmap_sel.c b/audio/chmap_sel.c
new file mode 100644
index 0000000000..8e5be5c86e
--- /dev/null
+++ b/audio/chmap_sel.c
@@ -0,0 +1,210 @@
+/*
+ * This file is part of mpv.
+ *
+ * mpv is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * mpv 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 General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with mpv.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include <stdlib.h>
+#include <assert.h>
+
+#include "chmap_sel.h"
+
+// 5.1 and 5.1(side) are practically the same. It doesn't make much sense to
+// reject either of them.
+static const int replaceable_speakers[][2] = {
+    {MP_SPEAKER_ID_SL, MP_SPEAKER_ID_BL},
+    {MP_SPEAKER_ID_SR, MP_SPEAKER_ID_BR},
+    {-1},
+};
+
+// list[] contains a list of speaker pairs, with each pair indicating how
+// a speaker can be swapped for another speaker. Try to replace speakers from
+// the left of the list with the ones on the right, or the other way around.
+static bool replace_speakers(struct mp_chmap *map, const int list[][2])
+{
+    if (!mp_chmap_is_valid(map))
+        return false;
+    for (int dir = 0; dir < 2; dir++) {
+        int from = dir ? 0 : 1;
+        int to   = dir ? 1 : 0;
+        bool replaced = false;
+        struct mp_chmap t = *map;
+        for (int n = 0; n < t.num; n++) {
+            for (int i = 0; list[i][0] != -1; i++) {
+                if (t.speaker[n] == list[i][from]) {
+                    t.speaker[n] = list[i][to];
+                    replaced = true;
+                    break;
+                }
+            }
+        }
+        if (replaced && mp_chmap_is_valid(&t)) {
+            *map = t;
+            return true;
+        }
+    }
+    return false;
+}
+
+// Allow all channel layouts that can be expressed with mp_chmap.
+// (By default, all layouts are rejected.)
+void mp_chmap_sel_add_any(struct mp_chmap_sel *s)
+{
+    s->allow_any = true;
+}
+
+// Allow all waveext formats, and force waveext channel order.
+void mp_chmap_sel_add_waveext(struct mp_chmap_sel *s)
+{
+    s->allow_waveext = true;
+}
+
+void mp_chmap_sel_add_alsa_def(struct mp_chmap_sel *s)
+{
+    for (int n = 0; n < MP_NUM_CHANNELS; n++) {
+        struct mp_chmap t;
+        mp_chmap_from_channels_alsa(&t, n);
+        if (t.num)
+            mp_chmap_sel_add_map(s, &t);
+    }
+}
+
+#define ARRAY_LEN(x) (sizeof(x) / sizeof((x)[0]))
+
+// Add a channel map that should be allowed.
+void mp_chmap_sel_add_map(struct mp_chmap_sel *s, const struct mp_chmap *map)
+{
+    assert(s->num_chmaps < ARRAY_LEN(s->chmaps));
+    if (mp_chmap_is_valid(map))
+        s->chmaps[s->num_chmaps++] = *map;
+}
+
+// Allow all waveext formats in default order.
+void mp_chmap_sel_add_waveext_def(struct mp_chmap_sel *s)
+{
+    for (int n = 1; n < MP_NUM_CHANNELS; n++) {
+        struct mp_chmap map;
+        mp_chmap_from_channels(&map, n);
+        mp_chmap_sel_add_map(s, &map);
+    }
+}
+
+// Whitelist a speaker (MP_SPEAKER_ID_...). All layouts that contain whitelisted
+// speakers are allowed.
+void mp_chmap_sel_add_speaker(struct mp_chmap_sel *s, int id)
+{
+    assert(id >= 0 && id < MP_SPEAKER_ID_COUNT);
+    s->speakers[id] = true;
+}
+
+static bool test_speakers(const struct mp_chmap_sel *s, struct mp_chmap *map)
+{
+    for (int n = 0; n < map->num; n++) {
+        if (!s->speakers[map->speaker[n]])
+            return false;
+    }
+    return true;
+}
+
+static bool test_maps(const struct mp_chmap_sel *s, struct mp_chmap *map)
+{
+    for (int n = 0; n < s->num_chmaps; n++) {
+        if (mp_chmap_equals_reordered(&s->chmaps[n], map)) {
+            *map = s->chmaps[n];
+            return true;
+        }
+    }
+    return false;
+}
+
+static bool test_waveext(const struct mp_chmap_sel *s, struct mp_chmap *map)
+{
+    if (s->allow_waveext) {
+        struct mp_chmap t = *map;
+        mp_chmap_reorder_to_waveext(&t);
+        if (mp_chmap_is_waveext(&t)) {
+            *map = t;
+            return true;
+        }
+    }
+    return false;
+}
+
+static bool test_layout(const struct mp_chmap_sel *s, struct mp_chmap *map)
+{
+    if (!mp_chmap_is_valid(map))
+        return false;
+
+    return s->allow_any || test_waveext(s, map) || test_speakers(s, map) ||
+           test_maps(s, map);
+}
+
+// Determine which channel map to use given a source channel map, and various
+// parameters restricting possible choices. If the map doesn't match, select
+// a fallback and set it.
+// If no matching layout is found, a reordered layout may be returned.
+// If that is not possible, a fallback for up/downmixing may be returned.
+// If no choice is possible, set *map to empty.
+bool mp_chmap_sel_adjust(const struct mp_chmap_sel *s, struct mp_chmap *map)
+{
+    if (test_layout(s, map))
+        return true;
+    if (mp_chmap_is_unknown(map)) {
+        struct mp_chmap t = {0};
+        if (mp_chmap_sel_get_def(s, &t, map->num) && test_layout(s, &t)) {
+            *map = t;
+            return true;
+        }
+    }
+    // 5.1 <-> 5.1(side)
+    if (replace_speakers(map, replaceable_speakers) && test_layout(s, map))
+        return true;
+    // Fallback to mono/stereo as last resort
+    if (map->num == 1) {
+        *map = (struct mp_chmap) MP_CHMAP_INIT_MONO;
+    } else if (map->num >= 2) {
+        *map = (struct mp_chmap) MP_CHMAP_INIT_STEREO;
+    }
+    if (test_layout(s, map))
+        return true;
+    *map = (struct mp_chmap) {0};
+    return false;
+}
+
+// Set map to a default layout with num channels. Used for audio APIs that
+// return a channel count as part of format negotiation, but give no
+// information about the channel layout.
+// If the channel count is correct, do nothing and leave *map untouched.
+bool mp_chmap_sel_get_def(const struct mp_chmap_sel *s, struct mp_chmap *map,
+                          int num)
+{
+    if (map->num != num) {
+        *map = (struct mp_chmap) {0};
+        // Set of speakers or waveext might allow it.
+        struct mp_chmap t;
+        mp_chmap_from_channels(&t, num);
+        mp_chmap_reorder_to_waveext(&t);
+        if (test_layout(s, &t)) {
+            *map = t;
+        } else {
+            for (int n = 0; n < s->num_chmaps; n++) {
+                if (s->chmaps[n].num == num) {
+                    *map = s->chmaps[n];
+                    break;
+                }
+            }
+        }
+    }
+    return map->num > 0;
+}
diff --git a/audio/chmap_sel.h b/audio/chmap_sel.h
new file mode 100644
index 0000000000..c9d75196a5
--- /dev/null
+++ b/audio/chmap_sel.h
@@ -0,0 +1,43 @@
+/*
+ * This file is part of mpv.
+ *
+ * mpv is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * mpv 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 General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with mpv.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#ifndef MP_CHMAP_SEL_H
+#define MP_CHMAP_SEL_H
+
+#include <stdbool.h>
+
+#include "chmap.h"
+
+struct mp_chmap_sel {
+    // should be considered opaque
+    bool allow_any, allow_waveext;
+    bool speakers[MP_SPEAKER_ID_COUNT];
+    struct mp_chmap chmaps[20];
+    int num_chmaps;
+};
+
+void mp_chmap_sel_add_any(struct mp_chmap_sel *s);
+void mp_chmap_sel_add_waveext(struct mp_chmap_sel *s);
+void mp_chmap_sel_add_waveext_def(struct mp_chmap_sel *s);
+void mp_chmap_sel_add_alsa_def(struct mp_chmap_sel *s);
+void mp_chmap_sel_add_map(struct mp_chmap_sel *s, const struct mp_chmap *map);
+void mp_chmap_sel_add_speaker(struct mp_chmap_sel *s, int id);
+bool mp_chmap_sel_adjust(const struct mp_chmap_sel *s, struct mp_chmap *map);
+bool mp_chmap_sel_get_def(const struct mp_chmap_sel *s, struct mp_chmap *map,
+                          int num);
+
+#endif
diff --git a/audio/out/ao.c b/audio/out/ao.c
index bf9b47a14e..10badcfa07 100644
--- a/audio/out/ao.c
+++ b/audio/out/ao.c
@@ -250,7 +250,17 @@ void ao_resume(struct ao *ao)
         ao->driver->resume(ao);
 }
 
+bool ao_chmap_sel_adjust(struct ao *ao, const struct mp_chmap_sel *s,
+                         struct mp_chmap *map)
+{
+    return mp_chmap_sel_adjust(s, map);
+}
 
+bool ao_chmap_sel_get_def(struct ao *ao, const struct mp_chmap_sel *s,
+                          struct mp_chmap *map, int num)
+{
+    return mp_chmap_sel_get_def(s, map, num);
+}
 
 int old_ao_init(struct ao *ao, char *params)
 {
diff --git a/audio/out/ao.h b/audio/out/ao.h
index 50f121bec2..d908841457 100644
--- a/audio/out/ao.h
+++ b/audio/out/ao.h
@@ -24,6 +24,7 @@
 #include "core/bstr.h"
 #include "core/mp_common.h"
 #include "audio/chmap.h"
+#include "audio/chmap_sel.h"
 
 enum aocontrol {
     // _VOLUME commands take struct ao_control_vol pointer for input/output.
@@ -121,6 +122,11 @@ void ao_reset(struct ao *ao);
 void ao_pause(struct ao *ao);
 void ao_resume(struct ao *ao);
 
+bool ao_chmap_sel_adjust(struct ao *ao, const struct mp_chmap_sel *s,
+                         struct mp_chmap *map);
+bool ao_chmap_sel_get_def(struct ao *ao, const struct mp_chmap_sel *s,
+                          struct mp_chmap *map, int num);
+
 int old_ao_control(struct ao *ao, enum aocontrol cmd, void *arg);
 int old_ao_init(struct ao *ao, char *params);
 void old_ao_uninit(struct ao *ao, bool cut_audio);