lavu/opt: add flag to return NULL when applicable in av_opt_get

Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavutil/opt.c

@@ -666,12 +666,20 @@ int av_opt_get(void *obj, const char *name, int search_flags, uint8_t **out_val)
     case AV_OPT_TYPE_RATIONAL:  ret = snprintf(buf, sizeof(buf), "%d/%d",   ((AVRational*)dst)->num, ((AVRational*)dst)->den);break;
     case AV_OPT_TYPE_CONST:     ret = snprintf(buf, sizeof(buf), "%f" ,     o->default_val.dbl);break;
     case AV_OPT_TYPE_STRING:
-        if (*(uint8_t**)dst)
+        if (*(uint8_t**)dst) {
             *out_val = av_strdup(*(uint8_t**)dst);
-        else
+        } else if (search_flags & AV_OPT_ALLOW_NULL) {
+            *out_val = NULL;
+            return 0;
+        } else {
             *out_val = av_strdup("");
+        }
         return *out_val ? 0 : AVERROR(ENOMEM);
     case AV_OPT_TYPE_BINARY:
+        if (!*(uint8_t**)dst && (search_flags & AV_OPT_ALLOW_NULL)) {
+            *out_val = NULL;
+            return 0;
+        }
         len = *(int*)(((uint8_t *)dst) + sizeof(uint8_t *));
         if ((uint64_t)len*2 + 1 > INT_MAX)
             return AVERROR(EINVAL);

libavutil/opt.h

@@ -563,6 +563,12 @@ int av_opt_eval_q     (void *obj, const AVOption *o, const char *val, AVRational
  */
 #define AV_OPT_SEARCH_FAKE_OBJ   (1 << 1)
 
+/**
+ *  In av_opt_get, return NULL if the option has a pointer type and is set to NULL,
+ *  rather than returning an empty string.
+ */
+#define AV_OPT_ALLOW_NULL (1 << 2)
+
 /**
  *  Allows av_opt_query_ranges and av_opt_query_ranges_default to return more than
  *  one component for certain option types.
@@ -722,6 +728,10 @@ int av_opt_set_dict_val(void *obj, const char *name, const AVDictionary *val, in
  */
 /**
  * @note the returned string will be av_malloc()ed and must be av_free()ed by the caller
+ *
+ * @note if AV_OPT_ALLOW_NULL is set in search_flags in av_opt_get, and the option has
+ * AV_OPT_TYPE_STRING or AV_OPT_TYPE_BINARY and is set to NULL, *out_val will be set
+ * to NULL instead of an allocated empty string.
  */
 int av_opt_get         (void *obj, const char *name, int search_flags, uint8_t   **out_val);
 int av_opt_get_int     (void *obj, const char *name, int search_flags, int64_t    *out_val);

libavutil/version.h

@@ -56,7 +56,7 @@
  */
 
 #define LIBAVUTIL_VERSION_MAJOR  55
-#define LIBAVUTIL_VERSION_MINOR   2
+#define LIBAVUTIL_VERSION_MINOR   3
 #define LIBAVUTIL_VERSION_MICRO 100
 
 #define LIBAVUTIL_VERSION_INT   AV_VERSION_INT(LIBAVUTIL_VERSION_MAJOR, \