diff --git a/audio/audio.c b/audio/audio.c
index 263470261e..baf00c08b2 100644
--- a/audio/audio.c
+++ b/audio/audio.c
@@ -160,8 +160,8 @@ void mp_audio_realloc(struct mp_audio *mpa, int samples)
         if (!mpa->allocated[n] || size != mpa->allocated[n]->size) {
             if (av_buffer_realloc(&mpa->allocated[n], size) < 0)
                 abort(); // OOM
-            mpa->planes[n] = mpa->allocated[n]->data;
         }
+        mpa->planes[n] = mpa->allocated[n]->data;
     }
     for (int n = mpa->num_planes; n < MP_NUM_CHANNELS; n++) {
         av_buffer_unref(&mpa->allocated[n]);
@@ -192,8 +192,18 @@ int mp_audio_get_allocated_size(struct mp_audio *mpa)
 {
     int size = 0;
     for (int n = 0; n < mpa->num_planes; n++) {
-        int s = mpa->allocated[n] ? mpa->allocated[n]->size / mpa->sstride : 0;
-        size = n == 0 ? s : MPMIN(size, s);
+        for (int i = 0; i < MP_NUM_CHANNELS && mpa->allocated[i]; i++) {
+            uint8_t *start = mpa->allocated[i]->data;
+            uint8_t *end = start + mpa->allocated[i]->size;
+            uint8_t *plane = mpa->planes[n];
+            if (plane >= start && plane < end) {
+                int s = MPMIN((end - plane) / mpa->sstride, INT_MAX);
+                size = n == 0 ? s : MPMIN(size, s);
+                goto next;
+            }
+        }
+        return 0; // plane is not covered by any buffer
+    next: ;
     }
     return size;
 }
diff --git a/audio/audio.h b/audio/audio.h
index a633a15b4d..7bfffa7887 100644
--- a/audio/audio.h
+++ b/audio/audio.h
@@ -37,8 +37,11 @@ struct mp_audio {
     int num_planes;     // number of planes
     int bps;            // size of sub-samples (af_fmt2bps(format))
 
-    // private
+    // --- private
     bool readonly;
+    // These do not necessarily map directly to planes[]. They can have
+    // different order or count. There shouldn't be more buffers than planes.
+    // If allocated[n] is NULL, allocated[n+1] must also be NULL.
     struct AVBufferRef *allocated[MP_NUM_CHANNELS];
 };