libavformat/matroskaenc.c:649: error: Null Dereference
  pointer `mkv->md5_ctx` last assigned on line 648 could be null and is dereferenced by call to `av_md5_init()` at line 649, column 5.

libavformat/matroskaenc.c:641:1: start of procedure mkv_write_header()
639. }
640. 
641. static int mkv_write_header(AVFormatContext *s)
     ^
642. {
643.     MatroskaMuxContext *mkv = s->priv_data;

libavformat/matroskaenc.c:643:5: 
641. static int mkv_write_header(AVFormatContext *s)
642. {
643.     MatroskaMuxContext *mkv = s->priv_data;
         ^
644.     ByteIOContext *pb = s->pb;
645.     ebml_master ebml_header, segment_info;

libavformat/matroskaenc.c:644:5: 
642. {
643.     MatroskaMuxContext *mkv = s->priv_data;
644.     ByteIOContext *pb = s->pb;
         ^
645.     ebml_master ebml_header, segment_info;
646.     int ret;

libavformat/matroskaenc.c:648:5: 
646.     int ret;
647. 
648.     mkv->md5_ctx = av_mallocz(av_md5_size);
         ^
649.     av_md5_init(mkv->md5_ctx);
650. 

libavutil/mem.c:135:1: start of procedure av_mallocz()
  133. }
  134. 
  135. void *av_mallocz(unsigned int size)
       ^
  136. {
  137.     void *ptr = av_malloc(size);

libavutil/mem.c:137:5: 
  135. void *av_mallocz(unsigned int size)
  136. {
  137.     void *ptr = av_malloc(size);
           ^
  138.     if (ptr)
  139.         memset(ptr, 0, size);

libavutil/mem.c:43:1: start of procedure av_malloc()
    41.    linker will do it automatically */
    42. 
    43. void *av_malloc(unsigned int size)
        ^
    44. {
    45.     void *ptr = NULL;

libavutil/mem.c:45:5: 
    43. void *av_malloc(unsigned int size)
    44. {
    45.     void *ptr = NULL;
            ^
    46. #ifdef CONFIG_MEMALIGN_HACK
    47.     long diff;

libavutil/mem.c:51:8: Taking true branch
    49. 
    50.     /* let's disallow possible ambiguous cases */
    51.     if(size > (INT_MAX-16) )
               ^
    52.         return NULL;
    53. 

libavutil/mem.c:52:9: 
    50.     /* let's disallow possible ambiguous cases */
    51.     if(size > (INT_MAX-16) )
    52.         return NULL;
                ^
    53. 
    54. #ifdef CONFIG_MEMALIGN_HACK

libavutil/mem.c:95:1: return from a call to av_malloc
    93. #endif
    94.     return ptr;
    95. }
        ^
    96. 
    97. void *av_realloc(void *ptr, unsigned int size)

libavutil/mem.c:138:9: Taking false branch
  136. {
  137.     void *ptr = av_malloc(size);
  138.     if (ptr)
               ^
  139.         memset(ptr, 0, size);
  140.     return ptr;

libavutil/mem.c:140:5: 
  138.     if (ptr)
  139.         memset(ptr, 0, size);
  140.     return ptr;
           ^
  141. }
  142. 

libavutil/mem.c:141:1: return from a call to av_mallocz
  139.         memset(ptr, 0, size);
  140.     return ptr;
  141. }
       ^
  142. 
  143. char *av_strdup(const char *s)

libavformat/matroskaenc.c:649:5: 
647. 
648.     mkv->md5_ctx = av_mallocz(av_md5_size);
649.     av_md5_init(mkv->md5_ctx);
         ^
650. 
651.     ebml_header = start_ebml_master(pb, EBML_ID_HEADER, 0);

libavutil/md5.c:118:1: start of procedure av_md5_init()
  116. }
  117. 
  118. void av_md5_init(AVMD5 *ctx){
       ^
  119.     ctx->len    = 0;
  120. 

libavutil/md5.c:119:5: 
  117. 
  118. void av_md5_init(AVMD5 *ctx){
  119.     ctx->len    = 0;
           ^
  120. 
  121.     ctx->ABCD[0] = 0x10325476;
