ffmpeg.c:2593: error: Null Dereference
  pointer `mid` last assigned on line 2593 could be null and is dereferenced at line 2593, column 5.

ffmpeg.c:2585:1: start of procedure opt_metadata()
2583. }
2584. 
2585. static int opt_metadata(const char *opt, const char *arg)
      ^
2586. {
2587.     char *mid= strchr(arg, '=');

ffmpeg.c:2587:5: 
2585. static int opt_metadata(const char *opt, const char *arg)
2586. {
2587.     char *mid= strchr(arg, '=');
          ^
2588. 
2589.     if(!mid){

ffmpeg.c:2589:9: Taking true branch
2587.     char *mid= strchr(arg, '=');
2588. 
2589.     if(!mid){
              ^
2590.         fprintf(stderr, "Missing =\n");
2591.         av_exit(1);

ffmpeg.c:2590:9: 
2588. 
2589.     if(!mid){
2590.         fprintf(stderr, "Missing =\n");
              ^
2591.         av_exit(1);
2592.     }

ffmpeg.c:2591:9: Skipping av_exit(): empty list of specs
2589.     if(!mid){
2590.         fprintf(stderr, "Missing =\n");
2591.         av_exit(1);
              ^
2592.     }
2593.     *mid++= 0;

ffmpeg.c:2593:5: 
2591.         av_exit(1);
2592.     }
2593.     *mid++= 0;
          ^
2594. 
2595.     metadata_count++;
