Make av_log_ask_for_sample() accept a variable number of arguments.

libavcodec/avcodec.h

@@ -4116,7 +4116,7 @@ void av_log_missing_feature(void *avc, const char *feature, int want_sample);
  * a pointer to an AVClass struct
  * @param[in] msg string containing an optional message, or NULL if no message
  */
-void av_log_ask_for_sample(void *avc, const char *msg);
+void av_log_ask_for_sample(void *avc, const char *msg, ...);
 
 /**
  * Register the hardware accelerator hwaccel.

libavcodec/utils.c

@@ -1133,13 +1133,19 @@ void av_log_missing_feature(void *avc, const char *feature, int want_sample)
         av_log(avc, AV_LOG_WARNING, "\n");
 }
 
-void av_log_ask_for_sample(void *avc, const char *msg)
+void av_log_ask_for_sample(void *avc, const char *msg, ...)
 {
+    va_list argument_list;
+
+    va_start(argument_list, msg);
+
     if (msg)
-        av_log(avc, AV_LOG_WARNING, "%s ", msg);
+        av_vlog(avc, AV_LOG_WARNING, msg, argument_list);
     av_log(avc, AV_LOG_WARNING, "If you want to help, upload a sample "
             "of this file to ftp://upload.libav.org/incoming/ "
             "and contact the libav-devel mailing list.\n");
+
+    va_end(argument_list);
 }
 
 static AVHWAccel *first_hwaccel = NULL;