add new API pa_channel_map_init_extend() to synthesize a channel map if noone is known

src/pulse/channelmap.c

@@ -394,6 +394,34 @@ pa_channel_map* pa_channel_map_init_auto(pa_channel_map *m, unsigned channels, p
     }
 }
 
+pa_channel_map* pa_channel_map_init_extend(pa_channel_map *m, unsigned channels, pa_channel_map_def_t def) {
+    unsigned c;
+
+    pa_assert(m);
+    pa_assert(channels > 0);
+    pa_assert(channels <= PA_CHANNELS_MAX);
+
+    pa_channel_map_init(m);
+
+    for (c = channels; c > 0; c--) {
+
+        if (pa_channel_map_init_auto(m, c, def)) {
+            unsigned i = 0;
+
+            for (; c < channels; c++) {
+
+                m->map[c] = PA_CHANNEL_POSITION_AUX0 + i;
+                i++;
+            }
+
+            m->channels = channels;
+
+            return m;
+        }
+    }
+
+    return NULL;
+}
 
 const char* pa_channel_position_to_string(pa_channel_position_t pos) {
 

src/pulse/channelmap.h

@@ -166,10 +166,18 @@ pa_channel_map* pa_channel_map_init_mono(pa_channel_map *m);
 /** Initialize the specified channel map for stereophonic audio and return a pointer to it */
 pa_channel_map* pa_channel_map_init_stereo(pa_channel_map *m);
 
-/** Initialize the specified channel map for the specified number
- * of channels using default labels and return a pointer to it. */
+/** Initialize the specified channel map for the specified number of
+ * channels using default labels and return a pointer to it. This call
+ * will fail (return NULL) if there is no default channel map known for this
+ * specific number of channels and mapping. */
 pa_channel_map* pa_channel_map_init_auto(pa_channel_map *m, unsigned channels, pa_channel_map_def_t def);
 
+/** Similar to pa_channel_map_init_auto() but instead of failing if no
+ * default mapping is known with the specified parameters it will
+ * synthesize a mapping based on a known mapping with fewer channels
+ * and fill up the rest with AUX0...AUX31 channels  \since 0.9.11 */
+pa_channel_map* pa_channel_map_init_extend(pa_channel_map *m, unsigned channels, pa_channel_map_def_t def);
+
 /** Return a text label for the specified channel position */
 const char* pa_channel_position_to_string(pa_channel_position_t pos) PA_GCC_PURE;