ffmpeg.c:2553: error: Null Dereference
  pointer `mid` last assigned on line 2553 could be null and is dereferenced at line 2553, column 5.

ffmpeg.c:2545:1: start of procedure opt_metadata()
2543. }
2544. 
2545. static int opt_metadata(const char *opt, const char *arg)
      ^
2546. {
2547.     char *mid= strchr(arg, '=');

ffmpeg.c:2547:5: 
2545. static int opt_metadata(const char *opt, const char *arg)
2546. {
2547.     char *mid= strchr(arg, '=');
          ^
2548. 
2549.     if(!mid){

ffmpeg.c:2549:9: Taking true branch
2547.     char *mid= strchr(arg, '=');
2548. 
2549.     if(!mid){
              ^
2550.         fprintf(stderr, "Missing =\n");
2551.         av_exit(1);

ffmpeg.c:2550:9: 
2548. 
2549.     if(!mid){
2550.         fprintf(stderr, "Missing =\n");
              ^
2551.         av_exit(1);
2552.     }

ffmpeg.c:2551:9: Skipping av_exit(): empty list of specs
2549.     if(!mid){
2550.         fprintf(stderr, "Missing =\n");
2551.         av_exit(1);
              ^
2552.     }
2553.     *mid++= 0;

ffmpeg.c:2553:5: 
2551.         av_exit(1);
2552.     }
2553.     *mid++= 0;
          ^
2554. 
2555.     metadata_count++;
