avconv.c:1843: error: Null Dereference
  pointer `ist` last assigned on line 1841 could be null and is dereferenced at line 1843, column 34.

avconv.c:1838:1: start of procedure init_output_stream_streamcopy()
1836. }
1837. 
1838. static int init_output_stream_streamcopy(OutputStream *ost)
      ^
1839. {
1840.     OutputFile *of = output_files[ost->file_index];

avconv.c:1840:5: 
1838. static int init_output_stream_streamcopy(OutputStream *ost)
1839. {
1840.     OutputFile *of = output_files[ost->file_index];
          ^
1841.     InputStream *ist = get_input_stream(ost);
1842.     AVCodecParameters *par_dst = ost->st->codecpar;

avconv.c:1841:5: 
1839. {
1840.     OutputFile *of = output_files[ost->file_index];
1841.     InputStream *ist = get_input_stream(ost);
          ^
1842.     AVCodecParameters *par_dst = ost->st->codecpar;
1843.     AVCodecParameters *par_src = ist->st->codecpar;

avconv.c:1729:1: start of procedure get_input_stream()
  1727. }
  1728. 
  1729. static InputStream *get_input_stream(OutputStream *ost)
        ^
  1730. {
  1731.     if (ost->source_index >= 0)

avconv.c:1731:9: Taking false branch
  1729. static InputStream *get_input_stream(OutputStream *ost)
  1730. {
  1731.     if (ost->source_index >= 0)
                ^
  1732.         return input_streams[ost->source_index];
  1733. 

avconv.c:1734:9: Taking true branch
  1732.         return input_streams[ost->source_index];
  1733. 
  1734.     if (ost->filter) {
                ^
  1735.         FilterGraph *fg = ost->filter->graph;
  1736.         int i;

avconv.c:1735:9: 
  1733. 
  1734.     if (ost->filter) {
  1735.         FilterGraph *fg = ost->filter->graph;
                ^
  1736.         int i;
  1737. 

avconv.c:1738:14: 
  1736.         int i;
  1737. 
  1738.         for (i = 0; i < fg->nb_inputs; i++)
                     ^
  1739.             if (fg->inputs[i]->ist->dec_ctx->codec_type == ost->enc_ctx->codec_type)
  1740.                 return fg->inputs[i]->ist;

avconv.c:1738:21: Loop condition is true. Entering loop body
  1736.         int i;
  1737. 
  1738.         for (i = 0; i < fg->nb_inputs; i++)
                            ^
  1739.             if (fg->inputs[i]->ist->dec_ctx->codec_type == ost->enc_ctx->codec_type)
  1740.                 return fg->inputs[i]->ist;

avconv.c:1739:17: Taking false branch
  1737. 
  1738.         for (i = 0; i < fg->nb_inputs; i++)
  1739.             if (fg->inputs[i]->ist->dec_ctx->codec_type == ost->enc_ctx->codec_type)
                        ^
  1740.                 return fg->inputs[i]->ist;
  1741.     }

avconv.c:1738:40: 
  1736.         int i;
  1737. 
  1738.         for (i = 0; i < fg->nb_inputs; i++)
                                               ^
  1739.             if (fg->inputs[i]->ist->dec_ctx->codec_type == ost->enc_ctx->codec_type)
  1740.                 return fg->inputs[i]->ist;

avconv.c:1738:21: Loop condition is false. Leaving loop
  1736.         int i;
  1737. 
  1738.         for (i = 0; i < fg->nb_inputs; i++)
                            ^
  1739.             if (fg->inputs[i]->ist->dec_ctx->codec_type == ost->enc_ctx->codec_type)
  1740.                 return fg->inputs[i]->ist;

avconv.c:1743:5: 
  1741.     }
  1742. 
  1743.     return NULL;
            ^
  1744. }
  1745. 

avconv.c:1744:1: return from a call to get_input_stream
  1742. 
  1743.     return NULL;
  1744. }
        ^
  1745. 
  1746. /* open the muxer when all the streams are initialized */

avconv.c:1842:5: 
1840.     OutputFile *of = output_files[ost->file_index];
1841.     InputStream *ist = get_input_stream(ost);
1842.     AVCodecParameters *par_dst = ost->st->codecpar;
          ^
1843.     AVCodecParameters *par_src = ist->st->codecpar;
1844.     AVRational sar;

avconv.c:1843:5: 
1841.     InputStream *ist = get_input_stream(ost);
1842.     AVCodecParameters *par_dst = ost->st->codecpar;
1843.     AVCodecParameters *par_src = ist->st->codecpar;
          ^
1844.     AVRational sar;
1845.     uint32_t codec_tag = par_dst->codec_tag;
