avtools/avconv.c:1858: error: Null Dereference
  pointer `ist` last assigned on line 1856 could be null and is dereferenced at line 1858, column 34.

avtools/avconv.c:1853:1: start of procedure init_output_stream_streamcopy()
1851. }
1852. 
1853. static int init_output_stream_streamcopy(OutputStream *ost)
      ^
1854. {
1855.     OutputFile *of = output_files[ost->file_index];

avtools/avconv.c:1855:5: 
1853. static int init_output_stream_streamcopy(OutputStream *ost)
1854. {
1855.     OutputFile *of = output_files[ost->file_index];
          ^
1856.     InputStream *ist = get_input_stream(ost);
1857.     AVCodecParameters *par_dst = ost->st->codecpar;

avtools/avconv.c:1856:5: 
1854. {
1855.     OutputFile *of = output_files[ost->file_index];
1856.     InputStream *ist = get_input_stream(ost);
          ^
1857.     AVCodecParameters *par_dst = ost->st->codecpar;
1858.     AVCodecParameters *par_src = ist->st->codecpar;

avtools/avconv.c:1754:1: start of procedure get_input_stream()
  1752. }
  1753. 
  1754. static InputStream *get_input_stream(OutputStream *ost)
        ^
  1755. {
  1756.     if (ost->source_index >= 0)

avtools/avconv.c:1756:9: Taking false branch
  1754. static InputStream *get_input_stream(OutputStream *ost)
  1755. {
  1756.     if (ost->source_index >= 0)
                ^
  1757.         return input_streams[ost->source_index];
  1758. 

avtools/avconv.c:1759:9: Taking true branch
  1757.         return input_streams[ost->source_index];
  1758. 
  1759.     if (ost->filter) {
                ^
  1760.         FilterGraph *fg = ost->filter->graph;
  1761.         int i;

avtools/avconv.c:1760:9: 
  1758. 
  1759.     if (ost->filter) {
  1760.         FilterGraph *fg = ost->filter->graph;
                ^
  1761.         int i;
  1762. 

avtools/avconv.c:1763:14: 
  1761.         int i;
  1762. 
  1763.         for (i = 0; i < fg->nb_inputs; i++)
                     ^
  1764.             if (fg->inputs[i]->ist->dec_ctx->codec_type == ost->enc_ctx->codec_type)
  1765.                 return fg->inputs[i]->ist;

avtools/avconv.c:1763:21: Loop condition is true. Entering loop body
  1761.         int i;
  1762. 
  1763.         for (i = 0; i < fg->nb_inputs; i++)
                            ^
  1764.             if (fg->inputs[i]->ist->dec_ctx->codec_type == ost->enc_ctx->codec_type)
  1765.                 return fg->inputs[i]->ist;

avtools/avconv.c:1764:17: Taking false branch
  1762. 
  1763.         for (i = 0; i < fg->nb_inputs; i++)
  1764.             if (fg->inputs[i]->ist->dec_ctx->codec_type == ost->enc_ctx->codec_type)
                        ^
  1765.                 return fg->inputs[i]->ist;
  1766.     }

avtools/avconv.c:1763:40: 
  1761.         int i;
  1762. 
  1763.         for (i = 0; i < fg->nb_inputs; i++)
                                               ^
  1764.             if (fg->inputs[i]->ist->dec_ctx->codec_type == ost->enc_ctx->codec_type)
  1765.                 return fg->inputs[i]->ist;

avtools/avconv.c:1763:21: Loop condition is false. Leaving loop
  1761.         int i;
  1762. 
  1763.         for (i = 0; i < fg->nb_inputs; i++)
                            ^
  1764.             if (fg->inputs[i]->ist->dec_ctx->codec_type == ost->enc_ctx->codec_type)
  1765.                 return fg->inputs[i]->ist;

avtools/avconv.c:1768:5: 
  1766.     }
  1767. 
  1768.     return NULL;
            ^
  1769. }
  1770. 

avtools/avconv.c:1769:1: return from a call to get_input_stream
  1767. 
  1768.     return NULL;
  1769. }
        ^
  1770. 
  1771. /* open the muxer when all the streams are initialized */

avtools/avconv.c:1857:5: 
1855.     OutputFile *of = output_files[ost->file_index];
1856.     InputStream *ist = get_input_stream(ost);
1857.     AVCodecParameters *par_dst = ost->st->codecpar;
          ^
1858.     AVCodecParameters *par_src = ist->st->codecpar;
1859.     AVRational sar;

avtools/avconv.c:1858:5: 
1856.     InputStream *ist = get_input_stream(ost);
1857.     AVCodecParameters *par_dst = ost->st->codecpar;
1858.     AVCodecParameters *par_src = ist->st->codecpar;
          ^
1859.     AVRational sar;
1860.     uint32_t codec_tag = par_dst->codec_tag;
