add FF_API_URL_CLASS define to enable usage of URLContext as a AVClass

Originally committed as revision 24835 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavformat/avformat.h

@@ -45,6 +45,9 @@
 #ifndef FF_API_OLD_METADATA
 #define FF_API_OLD_METADATA  (LIBAVFORMAT_VERSION_MAJOR < 53)
 #endif
+#ifndef FF_API_URL_CLASS
+#define FF_API_URL_CLASS     (LIBAVFORMAT_VERSION_MAJOR >= 53)
+#endif
 
 /**
  * I return the LIBAVFORMAT_VERSION_INT constant.  You got

libavformat/avio.c

@@ -30,7 +30,7 @@
 #include "network.h"
 #endif
 
-#if LIBAVFORMAT_VERSION_MAJOR >= 53
+#if FF_API_URL_CLASS
 /** @name Logging context. */
 /*@{*/
 static const char *urlcontext_to_name(void *ptr)
@@ -109,7 +109,7 @@ static int url_alloc_for_protocol (URLContext **puc, struct URLProtocol *up,
         err = AVERROR(ENOMEM);
         goto fail;
     }
-#if LIBAVFORMAT_VERSION_MAJOR >= 53
+#if FF_API_URL_CLASS
     uc->av_class = &urlcontext_class;
 #endif
     uc->filename = (char *) &uc[1];

libavformat/avio.h

@@ -43,7 +43,7 @@
  * sizeof(URLContext) must not be used outside libav*.
  */
 typedef struct URLContext {
-#if LIBAVFORMAT_VERSION_MAJOR >= 53
+#if FF_API_URL_CLASS
     const AVClass *av_class; ///< information for av_log(). Set by url_open().
 #endif
     struct URLProtocol *prot;