ffmpeg.c:2819: error: Null Dereference
  pointer `mid` last assigned on line 2819 could be null and is dereferenced at line 2819, column 5.

ffmpeg.c:2811:1: start of procedure opt_metadata()
2809. }
2810. 
2811. static int opt_metadata(const char *opt, const char *arg)
      ^
2812. {
2813.     char *mid= strchr(arg, '=');

ffmpeg.c:2813:5: 
2811. static int opt_metadata(const char *opt, const char *arg)
2812. {
2813.     char *mid= strchr(arg, '=');
          ^
2814. 
2815.     if(!mid){

ffmpeg.c:2815:9: Taking true branch
2813.     char *mid= strchr(arg, '=');
2814. 
2815.     if(!mid){
              ^
2816.         fprintf(stderr, "Missing =\n");
2817.         ffmpeg_exit(1);

ffmpeg.c:2816:9: 
2814. 
2815.     if(!mid){
2816.         fprintf(stderr, "Missing =\n");
              ^
2817.         ffmpeg_exit(1);
2818.     }

ffmpeg.c:2817:9: Skipping ffmpeg_exit(): empty list of specs
2815.     if(!mid){
2816.         fprintf(stderr, "Missing =\n");
2817.         ffmpeg_exit(1);
              ^
2818.     }
2819.     *mid++= 0;

ffmpeg.c:2819:5: 
2817.         ffmpeg_exit(1);
2818.     }
2819.     *mid++= 0;
          ^
2820. 
2821.     av_metadata_set2(&metadata, arg, mid, 0);
