avutil/channel_layout: add av_channel_layout_custom_init()

Signed-off-by: Marton Balint <cus@passwd.hu>

doc/APIchanges

@@ -2,6 +2,9 @@ The last version increases of all libraries were on 2023-02-09
 
 API changes, most recent first:
 
+2024-02-xx - xxxxxxxxxx - lavu 58.37.100 - channel_layout.h
+  Add av_channel_layout_custom_init().
+
 2024-02-04 - xxxxxxxxxx - lavc 60.39.100 - packet.h
   Add AV_PKT_DATA_AMBIENT_VIEWING_ENVIRONMENT.
 

libavutil/channel_layout.c

@@ -398,6 +398,26 @@ int av_get_standard_channel_layout(unsigned index, uint64_t *layout,
 FF_ENABLE_DEPRECATION_WARNINGS
 #endif
 
+int av_channel_layout_custom_init(AVChannelLayout *channel_layout, int nb_channels)
+{
+    AVChannelCustom *map;
+
+    if (nb_channels <= 0)
+        return AVERROR(EINVAL);
+
+    map = av_calloc(nb_channels, sizeof(*channel_layout->u.map));
+    if (!map)
+        return AVERROR(ENOMEM);
+    for (int i = 0; i < nb_channels; i++)
+        map[i].id = AV_CHAN_UNKNOWN;
+
+    channel_layout->order       = AV_CHANNEL_ORDER_CUSTOM;
+    channel_layout->nb_channels = nb_channels;
+    channel_layout->u.map       = map;
+
+    return 0;
+}
+
 int av_channel_layout_from_mask(AVChannelLayout *channel_layout,
                                 uint64_t mask)
 {

libavutil/channel_layout.h

@@ -617,6 +617,23 @@ void av_channel_description_bprint(struct AVBPrint *bp, enum AVChannel channel_i
  */
 enum AVChannel av_channel_from_string(const char *name);
 
+/**
+ * Initialize a custom channel layout with the specified number of channels.
+ * The channel map will be allocated and the designation of all channels will
+ * be set to AV_CHAN_UNKNOWN.
+ *
+ * This is only a convenience helper function, a custom channel layout can also
+ * be constructed without using this.
+ *
+ * @param channel_layout the layout structure to be initialized
+ * @param nb_channels the number of channels
+ *
+ * @return 0 on success
+ *         AVERROR(EINVAL) if the number of channels <= 0
+ *         AVERROR(ENOMEM) if the channel map could not be allocated
+ */
+int av_channel_layout_custom_init(AVChannelLayout *channel_layout, int nb_channels);
+
 /**
  * Initialize a native channel layout from a bitmask indicating which channels
  * are present.

libavutil/version.h

@@ -79,8 +79,8 @@
  */
 
 #define LIBAVUTIL_VERSION_MAJOR  58
-#define LIBAVUTIL_VERSION_MINOR  36
-#define LIBAVUTIL_VERSION_MICRO 101
+#define LIBAVUTIL_VERSION_MINOR  37
+#define LIBAVUTIL_VERSION_MICRO 100
 
 #define LIBAVUTIL_VERSION_INT   AV_VERSION_INT(LIBAVUTIL_VERSION_MAJOR, \
                                                LIBAVUTIL_VERSION_MINOR, \