avconv.c:1817: error: Null Dereference
  pointer `ist` last assigned on line 1815 could be null and is dereferenced at line 1817, column 34.

avconv.c:1812:1: start of procedure init_output_stream_streamcopy()
1810. }
1811. 
1812. static int init_output_stream_streamcopy(OutputStream *ost)
      ^
1813. {
1814.     OutputFile *of = output_files[ost->file_index];

avconv.c:1814:5: 
1812. static int init_output_stream_streamcopy(OutputStream *ost)
1813. {
1814.     OutputFile *of = output_files[ost->file_index];
          ^
1815.     InputStream *ist = get_input_stream(ost);
1816.     AVCodecParameters *par_dst = ost->st->codecpar;

avconv.c:1815:5: 
1813. {
1814.     OutputFile *of = output_files[ost->file_index];
1815.     InputStream *ist = get_input_stream(ost);
          ^
1816.     AVCodecParameters *par_dst = ost->st->codecpar;
1817.     AVCodecParameters *par_src = ist->st->codecpar;

avconv.c:1703:1: start of procedure get_input_stream()
  1701. }
  1702. 
  1703. static InputStream *get_input_stream(OutputStream *ost)
        ^
  1704. {
  1705.     if (ost->source_index >= 0)

avconv.c:1705:9: Taking false branch
  1703. static InputStream *get_input_stream(OutputStream *ost)
  1704. {
  1705.     if (ost->source_index >= 0)
                ^
  1706.         return input_streams[ost->source_index];
  1707. 

avconv.c:1708:9: Taking true branch
  1706.         return input_streams[ost->source_index];
  1707. 
  1708.     if (ost->filter) {
                ^
  1709.         FilterGraph *fg = ost->filter->graph;
  1710.         int i;

avconv.c:1709:9: 
  1707. 
  1708.     if (ost->filter) {
  1709.         FilterGraph *fg = ost->filter->graph;
                ^
  1710.         int i;
  1711. 

avconv.c:1712:14: 
  1710.         int i;
  1711. 
  1712.         for (i = 0; i < fg->nb_inputs; i++)
                     ^
  1713.             if (fg->inputs[i]->ist->dec_ctx->codec_type == ost->enc_ctx->codec_type)
  1714.                 return fg->inputs[i]->ist;

avconv.c:1712:21: Loop condition is true. Entering loop body
  1710.         int i;
  1711. 
  1712.         for (i = 0; i < fg->nb_inputs; i++)
                            ^
  1713.             if (fg->inputs[i]->ist->dec_ctx->codec_type == ost->enc_ctx->codec_type)
  1714.                 return fg->inputs[i]->ist;

avconv.c:1713:17: Taking false branch
  1711. 
  1712.         for (i = 0; i < fg->nb_inputs; i++)
  1713.             if (fg->inputs[i]->ist->dec_ctx->codec_type == ost->enc_ctx->codec_type)
                        ^
  1714.                 return fg->inputs[i]->ist;
  1715.     }

avconv.c:1712:40: 
  1710.         int i;
  1711. 
  1712.         for (i = 0; i < fg->nb_inputs; i++)
                                               ^
  1713.             if (fg->inputs[i]->ist->dec_ctx->codec_type == ost->enc_ctx->codec_type)
  1714.                 return fg->inputs[i]->ist;

avconv.c:1712:21: Loop condition is false. Leaving loop
  1710.         int i;
  1711. 
  1712.         for (i = 0; i < fg->nb_inputs; i++)
                            ^
  1713.             if (fg->inputs[i]->ist->dec_ctx->codec_type == ost->enc_ctx->codec_type)
  1714.                 return fg->inputs[i]->ist;

avconv.c:1717:5: 
  1715.     }
  1716. 
  1717.     return NULL;
            ^
  1718. }
  1719. 

avconv.c:1718:1: return from a call to get_input_stream
  1716. 
  1717.     return NULL;
  1718. }
        ^
  1719. 
  1720. /* open the muxer when all the streams are initialized */

avconv.c:1816:5: 
1814.     OutputFile *of = output_files[ost->file_index];
1815.     InputStream *ist = get_input_stream(ost);
1816.     AVCodecParameters *par_dst = ost->st->codecpar;
          ^
1817.     AVCodecParameters *par_src = ist->st->codecpar;
1818.     AVRational sar;

avconv.c:1817:5: 
1815.     InputStream *ist = get_input_stream(ost);
1816.     AVCodecParameters *par_dst = ost->st->codecpar;
1817.     AVCodecParameters *par_src = ist->st->codecpar;
          ^
1818.     AVRational sar;
1819.     uint32_t codec_tag = par_dst->codec_tag;
