libavformat/matroskaenc.c:627: error: Null Dereference
  pointer `mkv->md5_ctx` last assigned on line 626 could be null and is dereferenced by call to `av_md5_init()` at line 627, column 5.

libavformat/matroskaenc.c:619:1: start of procedure mkv_write_header()
617. }
618. 
619. static int mkv_write_header(AVFormatContext *s)
     ^
620. {
621.     MatroskaMuxContext *mkv = s->priv_data;

libavformat/matroskaenc.c:621:5: 
619. static int mkv_write_header(AVFormatContext *s)
620. {
621.     MatroskaMuxContext *mkv = s->priv_data;
         ^
622.     ByteIOContext *pb = s->pb;
623.     ebml_master ebml_header, segment_info;

libavformat/matroskaenc.c:622:5: 
620. {
621.     MatroskaMuxContext *mkv = s->priv_data;
622.     ByteIOContext *pb = s->pb;
         ^
623.     ebml_master ebml_header, segment_info;
624.     int ret;

libavformat/matroskaenc.c:626:5: 
624.     int ret;
625. 
626.     mkv->md5_ctx = av_mallocz(av_md5_size);
         ^
627.     av_md5_init(mkv->md5_ctx);
628. 

libavutil/mem.c:132:1: start of procedure av_mallocz()
  130. }
  131. 
  132. void *av_mallocz(unsigned int size)
       ^
  133. {
  134.     void *ptr = av_malloc(size);

libavutil/mem.c:134:5: 
  132. void *av_mallocz(unsigned int size)
  133. {
  134.     void *ptr = av_malloc(size);
           ^
  135.     if (ptr)
  136.         memset(ptr, 0, size);

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

libavutil/mem.c:50:8: Taking true branch
    48. 
    49.     /* let's disallow possible ambiguous cases */
    50.     if(size > (INT_MAX-16) )
               ^
    51.         return NULL;
    52. 

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

libavutil/mem.c:92:1: return from a call to av_malloc
    90. #endif
    91.     return ptr;
    92. }
        ^
    93. 
    94. void *av_realloc(void *ptr, unsigned int size)

libavutil/mem.c:135:9: Taking false branch
  133. {
  134.     void *ptr = av_malloc(size);
  135.     if (ptr)
               ^
  136.         memset(ptr, 0, size);
  137.     return ptr;

libavutil/mem.c:137:5: 
  135.     if (ptr)
  136.         memset(ptr, 0, size);
  137.     return ptr;
           ^
  138. }
  139. 

libavutil/mem.c:138:1: return from a call to av_mallocz
  136.         memset(ptr, 0, size);
  137.     return ptr;
  138. }
       ^
  139. 
  140. char *av_strdup(const char *s)

libavformat/matroskaenc.c:627:5: 
625. 
626.     mkv->md5_ctx = av_mallocz(av_md5_size);
627.     av_md5_init(mkv->md5_ctx);
         ^
628. 
629.     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;
