ffmpeg.c:2820: error: Null Dereference
  pointer `mid` last assigned on line 2820 could be null and is dereferenced at line 2820, column 5.

ffmpeg.c:2812:1: start of procedure opt_metadata()
2810. }
2811. 
2812. static int opt_metadata(const char *opt, const char *arg)
      ^
2813. {
2814.     char *mid= strchr(arg, '=');

ffmpeg.c:2814:5: 
2812. static int opt_metadata(const char *opt, const char *arg)
2813. {
2814.     char *mid= strchr(arg, '=');
          ^
2815. 
2816.     if(!mid){

ffmpeg.c:2816:9: Taking true branch
2814.     char *mid= strchr(arg, '=');
2815. 
2816.     if(!mid){
              ^
2817.         fprintf(stderr, "Missing =\n");
2818.         ffmpeg_exit(1);

ffmpeg.c:2817:9: 
2815. 
2816.     if(!mid){
2817.         fprintf(stderr, "Missing =\n");
              ^
2818.         ffmpeg_exit(1);
2819.     }

ffmpeg.c:2818:9: Skipping ffmpeg_exit(): empty list of specs
2816.     if(!mid){
2817.         fprintf(stderr, "Missing =\n");
2818.         ffmpeg_exit(1);
              ^
2819.     }
2820.     *mid++= 0;

ffmpeg.c:2820:5: 
2818.         ffmpeg_exit(1);
2819.     }
2820.     *mid++= 0;
          ^
2821. 
2822.     av_metadata_set2(&metadata, arg, mid, 0);
