libavformat/rtsp.c:860: error: Null Dereference
  pointer `st` last assigned on line 851 could be null and is dereferenced at line 860, column 56.

libavformat/rtsp.c:847:1: start of procedure rtsp_open_transport_ctx()
845. }
846. 
847. static int
     ^
848. rtsp_open_transport_ctx(AVFormatContext *s, RTSPStream *rtsp_st)
849. {

libavformat/rtsp.c:850:5: 
848. rtsp_open_transport_ctx(AVFormatContext *s, RTSPStream *rtsp_st)
849. {
850.     RTSPState *rt = s->priv_data;
         ^
851.     AVStream *st = NULL;
852. 

libavformat/rtsp.c:851:5: 
849. {
850.     RTSPState *rt = s->priv_data;
851.     AVStream *st = NULL;
         ^
852. 
853.     /* open the RTP context */

libavformat/rtsp.c:854:9: Taking false branch
852. 
853.     /* open the RTP context */
854.     if (rtsp_st->stream_index >= 0)
             ^
855.         st = s->streams[rtsp_st->stream_index];
856.     if (!st)

libavformat/rtsp.c:856:10: Taking true branch
854.     if (rtsp_st->stream_index >= 0)
855.         st = s->streams[rtsp_st->stream_index];
856.     if (!st)
              ^
857.         s->ctx_flags |= AVFMTCTX_NOHEADER;
858. 

libavformat/rtsp.c:857:9: 
855.         st = s->streams[rtsp_st->stream_index];
856.     if (!st)
857.         s->ctx_flags |= AVFMTCTX_NOHEADER;
             ^
858. 
859.     if (rt->transport == RTSP_TRANSPORT_RDT)

libavformat/rtsp.c:859:9: Taking true branch
857.         s->ctx_flags |= AVFMTCTX_NOHEADER;
858. 
859.     if (rt->transport == RTSP_TRANSPORT_RDT)
             ^
860.         rtsp_st->transport_priv = ff_rdt_parse_open(s, st->index,
861.                                             rtsp_st->dynamic_protocol_context,

libavformat/rtsp.c:860:9: 
858. 
859.     if (rt->transport == RTSP_TRANSPORT_RDT)
860.         rtsp_st->transport_priv = ff_rdt_parse_open(s, st->index,
             ^
861.                                             rtsp_st->dynamic_protocol_context,
862.                                             rtsp_st->dynamic_handler);

static int
rtsp_open_transport_ctx(AVFormatContext *s, RTSPStream *rtsp_st)
{
    RTSPState *rt = s->priv_data;
    AVStream *st = NULL;
    if (rtsp_st->stream_index >= 0)
        st = s->streams[rtsp_st->stream_index];
    if (!st)
        s->ctx_flags |= AVFMTCTX_NOHEADER;
    if (rt->transport == RTSP_TRANSPORT_RDT)
        rtsp_st->transport_priv = ff_rdt_parse_open(s, st->index,
                                            rtsp_st->dynamic_protocol_context,
                                            rtsp_st->dynamic_handler);
    else
        rtsp_st->transport_priv = rtp_parse_open(s, st, rtsp_st->rtp_handle,
                                         rtsp_st->sdp_payload_type,
                                         &rtsp_st->rtp_payload_data);
    if (!rtsp_st->transport_priv) {
         return AVERROR(ENOMEM);
    } else if (rt->transport != RTSP_TRANSPORT_RDT) {
        if(rtsp_st->dynamic_handler) {
            rtp_parse_set_dynamic_protocol(rtsp_st->transport_priv,
                                           rtsp_st->dynamic_protocol_context,
                                           rtsp_st->dynamic_handler);
        }
    }
    return 0;
}
['static int\nrtsp_open_transport_ctx(AVFormatContext *s, RTSPStream *rtsp_st)\n{\n    RTSPState *rt = s->priv_data;\n    AVStream *st = NULL;\n    if (rtsp_st->stream_index >= 0)\n        st = s->streams[rtsp_st->stream_index];\n    if (!st)\n        s->ctx_flags |= AVFMTCTX_NOHEADER;\n    if (rt->transport == RTSP_TRANSPORT_RDT)\n        rtsp_st->transport_priv = ff_rdt_parse_open(s, st->index,\n                                            rtsp_st->dynamic_protocol_context,\n                                            rtsp_st->dynamic_handler);\n    else\n        rtsp_st->transport_priv = rtp_parse_open(s, st, rtsp_st->rtp_handle,\n                                         rtsp_st->sdp_payload_type,\n                                         &rtsp_st->rtp_payload_data);\n    if (!rtsp_st->transport_priv) {\n         return AVERROR(ENOMEM);\n    } else if (rt->transport != RTSP_TRANSPORT_RDT) {\n        if(rtsp_st->dynamic_handler) {\n            rtp_parse_set_dynamic_protocol(rtsp_st->transport_priv,\n                                           rtsp_st->dynamic_protocol_context,\n                                           rtsp_st->dynamic_handler);\n        }\n    }\n    return 0;\n}']