avtools/avconv.c:1852: error: Null Dereference
  pointer `ist` last assigned on line 1850 could be null and is dereferenced at line 1852, column 34.

avtools/avconv.c:1847:1: start of procedure init_output_stream_streamcopy()
1845. }
1846. 
1847. static int init_output_stream_streamcopy(OutputStream *ost)
      ^
1848. {
1849.     OutputFile *of = output_files[ost->file_index];

avtools/avconv.c:1849:5: 
1847. static int init_output_stream_streamcopy(OutputStream *ost)
1848. {
1849.     OutputFile *of = output_files[ost->file_index];
          ^
1850.     InputStream *ist = get_input_stream(ost);
1851.     AVCodecParameters *par_dst = ost->st->codecpar;

avtools/avconv.c:1850:5: 
1848. {
1849.     OutputFile *of = output_files[ost->file_index];
1850.     InputStream *ist = get_input_stream(ost);
          ^
1851.     AVCodecParameters *par_dst = ost->st->codecpar;
1852.     AVCodecParameters *par_src = ist->st->codecpar;

avtools/avconv.c:1748:1: start of procedure get_input_stream()
  1746. }
  1747. 
  1748. static InputStream *get_input_stream(OutputStream *ost)
        ^
  1749. {
  1750.     if (ost->source_index >= 0)

avtools/avconv.c:1750:9: Taking false branch
  1748. static InputStream *get_input_stream(OutputStream *ost)
  1749. {
  1750.     if (ost->source_index >= 0)
                ^
  1751.         return input_streams[ost->source_index];
  1752. 

avtools/avconv.c:1753:9: Taking true branch
  1751.         return input_streams[ost->source_index];
  1752. 
  1753.     if (ost->filter) {
                ^
  1754.         FilterGraph *fg = ost->filter->graph;
  1755.         int i;

avtools/avconv.c:1754:9: 
  1752. 
  1753.     if (ost->filter) {
  1754.         FilterGraph *fg = ost->filter->graph;
                ^
  1755.         int i;
  1756. 

avtools/avconv.c:1757:14: 
  1755.         int i;
  1756. 
  1757.         for (i = 0; i < fg->nb_inputs; i++)
                     ^
  1758.             if (fg->inputs[i]->ist->dec_ctx->codec_type == ost->enc_ctx->codec_type)
  1759.                 return fg->inputs[i]->ist;

avtools/avconv.c:1757:21: Loop condition is true. Entering loop body
  1755.         int i;
  1756. 
  1757.         for (i = 0; i < fg->nb_inputs; i++)
                            ^
  1758.             if (fg->inputs[i]->ist->dec_ctx->codec_type == ost->enc_ctx->codec_type)
  1759.                 return fg->inputs[i]->ist;

avtools/avconv.c:1758:17: Taking false branch
  1756. 
  1757.         for (i = 0; i < fg->nb_inputs; i++)
  1758.             if (fg->inputs[i]->ist->dec_ctx->codec_type == ost->enc_ctx->codec_type)
                        ^
  1759.                 return fg->inputs[i]->ist;
  1760.     }

avtools/avconv.c:1757:40: 
  1755.         int i;
  1756. 
  1757.         for (i = 0; i < fg->nb_inputs; i++)
                                               ^
  1758.             if (fg->inputs[i]->ist->dec_ctx->codec_type == ost->enc_ctx->codec_type)
  1759.                 return fg->inputs[i]->ist;

avtools/avconv.c:1757:21: Loop condition is false. Leaving loop
  1755.         int i;
  1756. 
  1757.         for (i = 0; i < fg->nb_inputs; i++)
                            ^
  1758.             if (fg->inputs[i]->ist->dec_ctx->codec_type == ost->enc_ctx->codec_type)
  1759.                 return fg->inputs[i]->ist;

avtools/avconv.c:1762:5: 
  1760.     }
  1761. 
  1762.     return NULL;
            ^
  1763. }
  1764. 

avtools/avconv.c:1763:1: return from a call to get_input_stream
  1761. 
  1762.     return NULL;
  1763. }
        ^
  1764. 
  1765. /* open the muxer when all the streams are initialized */

avtools/avconv.c:1851:5: 
1849.     OutputFile *of = output_files[ost->file_index];
1850.     InputStream *ist = get_input_stream(ost);
1851.     AVCodecParameters *par_dst = ost->st->codecpar;
          ^
1852.     AVCodecParameters *par_src = ist->st->codecpar;
1853.     AVRational sar;

avtools/avconv.c:1852:5: 
1850.     InputStream *ist = get_input_stream(ost);
1851.     AVCodecParameters *par_dst = ost->st->codecpar;
1852.     AVCodecParameters *par_src = ist->st->codecpar;
          ^
1853.     AVRational sar;
1854.     uint32_t codec_tag = par_dst->codec_tag;
