avtools/avconv.c:1845: error: Null Dereference
  pointer `ist` last assigned on line 1843 could be null and is dereferenced at line 1845, column 34.

avtools/avconv.c:1840:1: start of procedure init_output_stream_streamcopy()
1838. }
1839. 
1840. static int init_output_stream_streamcopy(OutputStream *ost)
      ^
1841. {
1842.     OutputFile *of = output_files[ost->file_index];

avtools/avconv.c:1842:5: 
1840. static int init_output_stream_streamcopy(OutputStream *ost)
1841. {
1842.     OutputFile *of = output_files[ost->file_index];
          ^
1843.     InputStream *ist = get_input_stream(ost);
1844.     AVCodecParameters *par_dst = ost->st->codecpar;

avtools/avconv.c:1843:5: 
1841. {
1842.     OutputFile *of = output_files[ost->file_index];
1843.     InputStream *ist = get_input_stream(ost);
          ^
1844.     AVCodecParameters *par_dst = ost->st->codecpar;
1845.     AVCodecParameters *par_src = ist->st->codecpar;

avtools/avconv.c:1741:1: start of procedure get_input_stream()
  1739. }
  1740. 
  1741. static InputStream *get_input_stream(OutputStream *ost)
        ^
  1742. {
  1743.     if (ost->source_index >= 0)

avtools/avconv.c:1743:9: Taking false branch
  1741. static InputStream *get_input_stream(OutputStream *ost)
  1742. {
  1743.     if (ost->source_index >= 0)
                ^
  1744.         return input_streams[ost->source_index];
  1745. 

avtools/avconv.c:1746:9: Taking true branch
  1744.         return input_streams[ost->source_index];
  1745. 
  1746.     if (ost->filter) {
                ^
  1747.         FilterGraph *fg = ost->filter->graph;
  1748.         int i;

avtools/avconv.c:1747:9: 
  1745. 
  1746.     if (ost->filter) {
  1747.         FilterGraph *fg = ost->filter->graph;
                ^
  1748.         int i;
  1749. 

avtools/avconv.c:1750:14: 
  1748.         int i;
  1749. 
  1750.         for (i = 0; i < fg->nb_inputs; i++)
                     ^
  1751.             if (fg->inputs[i]->ist->dec_ctx->codec_type == ost->enc_ctx->codec_type)
  1752.                 return fg->inputs[i]->ist;

avtools/avconv.c:1750:21: Loop condition is true. Entering loop body
  1748.         int i;
  1749. 
  1750.         for (i = 0; i < fg->nb_inputs; i++)
                            ^
  1751.             if (fg->inputs[i]->ist->dec_ctx->codec_type == ost->enc_ctx->codec_type)
  1752.                 return fg->inputs[i]->ist;

avtools/avconv.c:1751:17: Taking false branch
  1749. 
  1750.         for (i = 0; i < fg->nb_inputs; i++)
  1751.             if (fg->inputs[i]->ist->dec_ctx->codec_type == ost->enc_ctx->codec_type)
                        ^
  1752.                 return fg->inputs[i]->ist;
  1753.     }

avtools/avconv.c:1750:40: 
  1748.         int i;
  1749. 
  1750.         for (i = 0; i < fg->nb_inputs; i++)
                                               ^
  1751.             if (fg->inputs[i]->ist->dec_ctx->codec_type == ost->enc_ctx->codec_type)
  1752.                 return fg->inputs[i]->ist;

avtools/avconv.c:1750:21: Loop condition is false. Leaving loop
  1748.         int i;
  1749. 
  1750.         for (i = 0; i < fg->nb_inputs; i++)
                            ^
  1751.             if (fg->inputs[i]->ist->dec_ctx->codec_type == ost->enc_ctx->codec_type)
  1752.                 return fg->inputs[i]->ist;

avtools/avconv.c:1755:5: 
  1753.     }
  1754. 
  1755.     return NULL;
            ^
  1756. }
  1757. 

avtools/avconv.c:1756:1: return from a call to get_input_stream
  1754. 
  1755.     return NULL;
  1756. }
        ^
  1757. 
  1758. /* open the muxer when all the streams are initialized */

avtools/avconv.c:1844:5: 
1842.     OutputFile *of = output_files[ost->file_index];
1843.     InputStream *ist = get_input_stream(ost);
1844.     AVCodecParameters *par_dst = ost->st->codecpar;
          ^
1845.     AVCodecParameters *par_src = ist->st->codecpar;
1846.     AVRational sar;

avtools/avconv.c:1845:5: 
1843.     InputStream *ist = get_input_stream(ost);
1844.     AVCodecParameters *par_dst = ost->st->codecpar;
1845.     AVCodecParameters *par_src = ist->st->codecpar;
          ^
1846.     AVRational sar;
1847.     uint32_t codec_tag = par_dst->codec_tag;
