libavcodec/mpegvideo.c:1842: error: Null Dereference
  pointer `desc` last assigned on line 1841 could be null and is dereferenced at line 1842, column 22.

libavcodec/mpegvideo.c:1824:1: start of procedure ff_MPV_frame_end()
1822. 
1823. /* called after a frame has been decoded. */
1824. void ff_MPV_frame_end(MpegEncContext *s)
      ^
1825. {
1826. #if FF_API_XVMC

libavcodec/mpegvideo.c:1830:9: Taking false branch
1828.     /* redraw edges for the frame if decoding didn't complete */
1829.     // just to make sure that all data is rendered.
1830.     if (CONFIG_MPEG_XVMC_DECODER && s->avctx->xvmc_acceleration) {
              ^
1831.         ff_xvmc_field_end(s);
1832.     } else

libavcodec/mpegvideo.c:1835:9: Taking true branch
1833. FF_ENABLE_DEPRECATION_WARNINGS
1834. #endif /* FF_API_XVMC */
1835.     if (s->er.error_count  &&
              ^
1836.         !s->avctx->hwaccel &&
1837.         s->unrestricted_mv &&

libavcodec/mpegvideo.c:1836:10: Taking true branch
1834. #endif /* FF_API_XVMC */
1835.     if (s->er.error_count  &&
1836.         !s->avctx->hwaccel &&
               ^
1837.         s->unrestricted_mv &&
1838.         s->current_picture.reference &&

libavcodec/mpegvideo.c:1837:9: Taking true branch
1835.     if (s->er.error_count  &&
1836.         !s->avctx->hwaccel &&
1837.         s->unrestricted_mv &&
              ^
1838.         s->current_picture.reference &&
1839.         !s->intra_only &&

libavcodec/mpegvideo.c:1838:9: Taking true branch
1836.         !s->avctx->hwaccel &&
1837.         s->unrestricted_mv &&
1838.         s->current_picture.reference &&
              ^
1839.         !s->intra_only &&
1840.         !(s->flags & CODEC_FLAG_EMU_EDGE)) {

libavcodec/mpegvideo.c:1839:10: Taking true branch
1837.         s->unrestricted_mv &&
1838.         s->current_picture.reference &&
1839.         !s->intra_only &&
               ^
1840.         !(s->flags & CODEC_FLAG_EMU_EDGE)) {
1841.         const AVPixFmtDescriptor *desc = av_pix_fmt_desc_get(s->avctx->pix_fmt);

libavcodec/mpegvideo.c:1840:11: Taking true branch
1838.         s->current_picture.reference &&
1839.         !s->intra_only &&
1840.         !(s->flags & CODEC_FLAG_EMU_EDGE)) {
                ^
1841.         const AVPixFmtDescriptor *desc = av_pix_fmt_desc_get(s->avctx->pix_fmt);
1842.         int hshift = desc->log2_chroma_w;

libavcodec/mpegvideo.c:1841:9: 
1839.         !s->intra_only &&
1840.         !(s->flags & CODEC_FLAG_EMU_EDGE)) {
1841.         const AVPixFmtDescriptor *desc = av_pix_fmt_desc_get(s->avctx->pix_fmt);
              ^
1842.         int hshift = desc->log2_chroma_w;
1843.         int vshift = desc->log2_chroma_h;

libavutil/pixdesc.c:1507:1: start of procedure av_pix_fmt_desc_get()
  1505. }
  1506. 
  1507. const AVPixFmtDescriptor *av_pix_fmt_desc_get(enum AVPixelFormat pix_fmt)
        ^
  1508. {
  1509.     if (pix_fmt < 0 || pix_fmt >= AV_PIX_FMT_NB)

libavutil/pixdesc.c:1509:9: Taking false branch
  1507. const AVPixFmtDescriptor *av_pix_fmt_desc_get(enum AVPixelFormat pix_fmt)
  1508. {
  1509.     if (pix_fmt < 0 || pix_fmt >= AV_PIX_FMT_NB)
                ^
  1510.         return NULL;
  1511.     return &av_pix_fmt_descriptors[pix_fmt];

libavutil/pixdesc.c:1509:24: Taking true branch
  1507. const AVPixFmtDescriptor *av_pix_fmt_desc_get(enum AVPixelFormat pix_fmt)
  1508. {
  1509.     if (pix_fmt < 0 || pix_fmt >= AV_PIX_FMT_NB)
                               ^
  1510.         return NULL;
  1511.     return &av_pix_fmt_descriptors[pix_fmt];

libavutil/pixdesc.c:1510:9: 
  1508. {
  1509.     if (pix_fmt < 0 || pix_fmt >= AV_PIX_FMT_NB)
  1510.         return NULL;
                ^
  1511.     return &av_pix_fmt_descriptors[pix_fmt];
  1512. }

libavutil/pixdesc.c:1512:1: return from a call to av_pix_fmt_desc_get
  1510.         return NULL;
  1511.     return &av_pix_fmt_descriptors[pix_fmt];
  1512. }
        ^
  1513. 
  1514. const AVPixFmtDescriptor *av_pix_fmt_desc_next(const AVPixFmtDescriptor *prev)

libavcodec/mpegvideo.c:1842:9: 
1840.         !(s->flags & CODEC_FLAG_EMU_EDGE)) {
1841.         const AVPixFmtDescriptor *desc = av_pix_fmt_desc_get(s->avctx->pix_fmt);
1842.         int hshift = desc->log2_chroma_w;
              ^
1843.         int vshift = desc->log2_chroma_h;
1844.         s->dsp.draw_edges(s->current_picture.f.data[0], s->linesize,
