crypto: add decoding flag to options.

libavformat/crypto.c

@@ -45,9 +45,10 @@ typedef struct {
 } CryptoContext;
 
 #define OFFSET(x) offsetof(CryptoContext, x)
+#define D AV_OPT_FLAG_DECODING_PARAM
 static const AVOption options[] = {
-    {"key", "AES decryption key", OFFSET(key), AV_OPT_TYPE_BINARY },
-    {"iv",  "AES decryption initialization vector", OFFSET(iv),  AV_OPT_TYPE_BINARY },
+    {"key", "AES decryption key", OFFSET(key), AV_OPT_TYPE_BINARY, .flags = D },
+    {"iv",  "AES decryption initialization vector", OFFSET(iv),  AV_OPT_TYPE_BINARY, .flags = D },
     { NULL }
 };