avutil/iamf: add an AVOption for AVIAMFLayer.demixing_matrix

Plus a length field, to fulfill the requirements of AV_OPT_TYPE_FLAG_ARRAY options.

Signed-off-by: James Almer <jamrial@gmail.com>

doc/APIchanges

@@ -2,6 +2,9 @@ The last version increases of all libraries were on 2025-03-28
 
 API changes, most recent first:
 
+2025-12-29 - xxxxxxxxxx - lavu 60.21.100 - iamf.h
+  Add nb_demixing_matrix to AVIAMFLayer
+
 2025-12-xx - xxxxxxxxxx - lavc 62.23.100 - coedc_id.h
   Add AV_CODEC_ID_JPEGXS.
 

libavutil/iamf.c

@@ -239,6 +239,8 @@ AVIAMFParamDefinition *av_iamf_param_definition_alloc(enum AVIAMFParamDefinition
 //
 // Audio Element
 //
+static const AVOptionArrayDef demixing_matrix_def = { .def = "0|0", .size_max = (255 + 255) * 255, .sep = '|' };
+
 #undef OFFSET
 #define OFFSET(x) offsetof(AVIAMFLayer, x)
 static const AVOption layer_options[] = {
@@ -269,6 +271,8 @@ static const AVOption layer_options[] = {
                    { .i64 = AV_IAMF_AMBISONICS_MODE_MONO },       .unit = "ambisonics_mode" },
         { "projection", NULL, 0, AV_OPT_TYPE_CONST,
                    { .i64 = AV_IAMF_AMBISONICS_MODE_PROJECTION }, .unit = "ambisonics_mode" },
+    { "demixing_matrix", "set demixing_matrix", OFFSET(demixing_matrix), AV_OPT_TYPE_RATIONAL | AV_OPT_TYPE_FLAG_ARRAY,
+            { .arr = &demixing_matrix_def }, -1.0, 1.0, FLAGS },
     { NULL },
 };
 

libavutil/iamf.h

@@ -330,14 +330,17 @@ typedef struct AVIAMFLayer {
     /**
      * Demixing matrix as defined in section 3.6.3 of IAMF.
      *
-     * The length of the array is ch_layout.nb_channels multiplied by the sum of
-     * the amount of streams in the group plus the amount of streams in the group
-     * that are stereo.
-     *
      * May be set only if @ref ambisonics_mode == AV_IAMF_AMBISONICS_MODE_PROJECTION,
      * must be NULL otherwise.
      */
     AVRational *demixing_matrix;
+
+    /**
+     * The length of the Demixing matrix array. Must be ch_layout.nb_channels multiplied
+     * by the sum of the amount of streams in the group plus the amount of streams in
+     * the group that are stereo.
+     */
+    unsigned int nb_demixing_matrix;
 } AVIAMFLayer;
 
 

libavutil/version.h

@@ -79,7 +79,7 @@
  */
 
 #define LIBAVUTIL_VERSION_MAJOR  60
-#define LIBAVUTIL_VERSION_MINOR  20
+#define LIBAVUTIL_VERSION_MINOR  21
 #define LIBAVUTIL_VERSION_MICRO 100
 
 #define LIBAVUTIL_VERSION_INT   AV_VERSION_INT(LIBAVUTIL_VERSION_MAJOR, \