libavcodec/mpegvideo.c:1720: error: Null Dereference
  pointer `desc` last assigned on line 1719 could be null and is dereferenced at line 1720, column 22.

libavcodec/mpegvideo.c:1700:1: start of procedure ff_MPV_frame_end()
1698. /* generic function for encode/decode called after a
1699.  * frame has been coded/decoded. */
1700. void ff_MPV_frame_end(MpegEncContext *s)
      ^
1701. {
1702.     int i;

libavcodec/mpegvideo.c:1708:9: Taking false branch
1706.     /* redraw edges for the frame if decoding didn't complete */
1707.     // just to make sure that all data is rendered.
1708.     if (CONFIG_MPEG_XVMC_DECODER && s->avctx->xvmc_acceleration) {
              ^
1709.         ff_xvmc_field_end(s);
1710.     } else

libavcodec/mpegvideo.c:1713:10: Taking false branch
1711. FF_ENABLE_DEPRECATION_WARNINGS
1712. #endif /* FF_API_XVMC */
1713.     if ((s->er.error_count || s->encoding) &&
               ^
1714.         !s->avctx->hwaccel &&
1715.         s->unrestricted_mv &&

libavcodec/mpegvideo.c:1713:31: Taking true branch
1711. FF_ENABLE_DEPRECATION_WARNINGS
1712. #endif /* FF_API_XVMC */
1713.     if ((s->er.error_count || s->encoding) &&
                                    ^
1714.         !s->avctx->hwaccel &&
1715.         s->unrestricted_mv &&

libavcodec/mpegvideo.c:1714:10: Taking true branch
1712. #endif /* FF_API_XVMC */
1713.     if ((s->er.error_count || s->encoding) &&
1714.         !s->avctx->hwaccel &&
               ^
1715.         s->unrestricted_mv &&
1716.         s->current_picture.reference &&

libavcodec/mpegvideo.c:1715:9: Taking true branch
1713.     if ((s->er.error_count || s->encoding) &&
1714.         !s->avctx->hwaccel &&
1715.         s->unrestricted_mv &&
              ^
1716.         s->current_picture.reference &&
1717.         !s->intra_only &&

libavcodec/mpegvideo.c:1716:9: Taking true branch
1714.         !s->avctx->hwaccel &&
1715.         s->unrestricted_mv &&
1716.         s->current_picture.reference &&
              ^
1717.         !s->intra_only &&
1718.         !(s->flags & CODEC_FLAG_EMU_EDGE)) {

libavcodec/mpegvideo.c:1717:10: Taking true branch
1715.         s->unrestricted_mv &&
1716.         s->current_picture.reference &&
1717.         !s->intra_only &&
               ^
1718.         !(s->flags & CODEC_FLAG_EMU_EDGE)) {
1719.         const AVPixFmtDescriptor *desc = av_pix_fmt_desc_get(s->avctx->pix_fmt);

libavcodec/mpegvideo.c:1718:11: Taking true branch
1716.         s->current_picture.reference &&
1717.         !s->intra_only &&
1718.         !(s->flags & CODEC_FLAG_EMU_EDGE)) {
                ^
1719.         const AVPixFmtDescriptor *desc = av_pix_fmt_desc_get(s->avctx->pix_fmt);
1720.         int hshift = desc->log2_chroma_w;

libavcodec/mpegvideo.c:1719:9: 
1717.         !s->intra_only &&
1718.         !(s->flags & CODEC_FLAG_EMU_EDGE)) {
1719.         const AVPixFmtDescriptor *desc = av_pix_fmt_desc_get(s->avctx->pix_fmt);
              ^
1720.         int hshift = desc->log2_chroma_w;
1721.         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:1720:9: 
1718.         !(s->flags & CODEC_FLAG_EMU_EDGE)) {
1719.         const AVPixFmtDescriptor *desc = av_pix_fmt_desc_get(s->avctx->pix_fmt);
1720.         int hshift = desc->log2_chroma_w;
              ^
1721.         int vshift = desc->log2_chroma_h;
1722.         s->dsp.draw_edges(s->current_picture.f.data[0], s->linesize,
