lavfi: support unknown channel layouts.

libavfilter/formats.h

@@ -69,14 +69,45 @@ struct AVFilterFormats {
     struct AVFilterFormats ***refs; ///< references to this list
 };
 
+/**
+ * A list of supported channel layouts.
+ *
+ * The list works the same as AVFilterFormats, except for the following
+ * differences:
+ * - A list with all_layouts = 1 means all channel layouts with a known
+ *   disposition; nb_channel_layouts must then be 0.
+ * - A list with all_counts = 1 means all channel counts, with a known or
+ *   unknown disposition; nb_channel_layouts must then be 0 and all_layouts 1.
+ * - The list must not contain a layout with a known disposition and a
+ *   channel count with unknown disposition with the same number of channels
+ *   (e.g. AV_CH_LAYOUT_STEREO and FF_COUNT2LAYOUT(2).
+ */
 typedef struct AVFilterChannelLayouts {
     uint64_t *channel_layouts;  ///< list of channel layouts
     int    nb_channel_layouts;  ///< number of channel layouts
+    char all_layouts;           ///< accept any known channel layout
+    char all_counts;            ///< accept any channel layout or count
 
     unsigned refcount;          ///< number of references to this list
     struct AVFilterChannelLayouts ***refs; ///< references to this list
 } AVFilterChannelLayouts;
 
+/**
+ * Encode a channel count as a channel layout.
+ * FF_COUNT2LAYOUT(c) means any channel layout with c channels, with a known
+ * or unknown disposition.
+ * The result is only valid inside AVFilterChannelLayouts and immediately
+ * related functions.
+ */
+#define FF_COUNT2LAYOUT(c) (0x8000000000000000ULL | (c))
+
+/**
+ * Decode a channel count encoded as a channel layout.
+ * Return 0 if the channel layout was a real one.
+ */
+#define FF_LAYOUT2COUNT(l) (((l) & 0x8000000000000000ULL) ? \
+                           (int)((l) & 0x7FFFFFFF) : 0)
+
 /**
  * Return a channel layouts/samplerates list which contains the intersection of
  * the layouts/samplerates of a and b. Also, all the references of a, all the