libavcodec/mpegvideo.c:2243: error: Null Dereference
  pointer `desc` last assigned on line 2242 could be null and is dereferenced at line 2243, column 18.

libavcodec/mpegvideo.c:2237:1: start of procedure ff_draw_horiz_band()
2235.  * @param h is the normal height, this will be reduced automatically if needed for the last row
2236.  */
2237. void ff_draw_horiz_band(AVCodecContext *avctx, DSPContext *dsp, Picture *cur,
      ^
2238.                         Picture *last, int y, int h, int picture_structure,
2239.                         int first_field, int draw_edges, int low_delay,

libavcodec/mpegvideo.c:2242:5: 
2240.                         int v_edge_pos, int h_edge_pos)
2241. {
2242.     const AVPixFmtDescriptor *desc = av_pix_fmt_desc_get(avctx->pix_fmt);
          ^
2243.     int hshift = desc->log2_chroma_w;
2244.     int vshift = desc->log2_chroma_h;

libavutil/pixdesc.c:1440:1: start of procedure av_pix_fmt_desc_get()
  1438. }
  1439. 
  1440. const AVPixFmtDescriptor *av_pix_fmt_desc_get(enum AVPixelFormat pix_fmt)
        ^
  1441. {
  1442.     if (pix_fmt < 0 || pix_fmt >= AV_PIX_FMT_NB)

libavutil/pixdesc.c:1442:9: Taking false branch
  1440. const AVPixFmtDescriptor *av_pix_fmt_desc_get(enum AVPixelFormat pix_fmt)
  1441. {
  1442.     if (pix_fmt < 0 || pix_fmt >= AV_PIX_FMT_NB)
                ^
  1443.         return NULL;
  1444.     return &av_pix_fmt_descriptors[pix_fmt];

libavutil/pixdesc.c:1442:24: Taking true branch
  1440. const AVPixFmtDescriptor *av_pix_fmt_desc_get(enum AVPixelFormat pix_fmt)
  1441. {
  1442.     if (pix_fmt < 0 || pix_fmt >= AV_PIX_FMT_NB)
                               ^
  1443.         return NULL;
  1444.     return &av_pix_fmt_descriptors[pix_fmt];

libavutil/pixdesc.c:1443:9: 
  1441. {
  1442.     if (pix_fmt < 0 || pix_fmt >= AV_PIX_FMT_NB)
  1443.         return NULL;
                ^
  1444.     return &av_pix_fmt_descriptors[pix_fmt];
  1445. }

libavutil/pixdesc.c:1445:1: return from a call to av_pix_fmt_desc_get
  1443.         return NULL;
  1444.     return &av_pix_fmt_descriptors[pix_fmt];
  1445. }
        ^
  1446. 
  1447. const AVPixFmtDescriptor *av_pix_fmt_desc_next(const AVPixFmtDescriptor *prev)

libavcodec/mpegvideo.c:2243:5: 
2241. {
2242.     const AVPixFmtDescriptor *desc = av_pix_fmt_desc_get(avctx->pix_fmt);
2243.     int hshift = desc->log2_chroma_w;
          ^
2244.     int vshift = desc->log2_chroma_h;
2245.     const int field_pic = picture_structure != PICT_FRAME;
