ffmpeg.c:2815: error: Null Dereference
  pointer `mid` last assigned on line 2815 could be null and is dereferenced at line 2815, column 5.

ffmpeg.c:2807:1: start of procedure opt_metadata()
2805. }
2806. 
2807. static int opt_metadata(const char *opt, const char *arg)
      ^
2808. {
2809.     char *mid= strchr(arg, '=');

ffmpeg.c:2809:5: 
2807. static int opt_metadata(const char *opt, const char *arg)
2808. {
2809.     char *mid= strchr(arg, '=');
          ^
2810. 
2811.     if(!mid){

ffmpeg.c:2811:9: Taking true branch
2809.     char *mid= strchr(arg, '=');
2810. 
2811.     if(!mid){
              ^
2812.         fprintf(stderr, "Missing =\n");
2813.         ffmpeg_exit(1);

ffmpeg.c:2812:9: 
2810. 
2811.     if(!mid){
2812.         fprintf(stderr, "Missing =\n");
              ^
2813.         ffmpeg_exit(1);
2814.     }

ffmpeg.c:2813:9: Skipping ffmpeg_exit(): empty list of specs
2811.     if(!mid){
2812.         fprintf(stderr, "Missing =\n");
2813.         ffmpeg_exit(1);
              ^
2814.     }
2815.     *mid++= 0;

ffmpeg.c:2815:5: 
2813.         ffmpeg_exit(1);
2814.     }
2815.     *mid++= 0;
          ^
2816. 
2817.     av_metadata_set2(&metadata, arg, mid, 0);
