older libavcodecs don't have AV_LOG_TRACE AND AV_LOG_MAX_OFFSET

src/zm_ffmpeg.cpp

@@ -43,10 +43,14 @@ void log_libav_callback( void *ptr, int level, const char *fmt, va_list vargs )
     log_level = Logger::DEBUG1;
   } else if ( level == AV_LOG_DEBUG ) { //48
     log_level = Logger::DEBUG2;
+#ifdef AV_LOG_TRACE
   } else if ( level == AV_LOG_TRACE ) {
     log_level = Logger::DEBUG8;
+#endif
+#ifdef AV_LOG_MAX_OFFSET
   } else if ( level == AV_LOG_MAX_OFFSET ) {
     log_level = Logger::DEBUG9;
+#endif
   } else {
     Error("Unknown log level %d", level);
   }