libavcodec/mpegvideo.c:1530: error: Null Dereference
  pointer `desc` last assigned on line 1529 could be null and is dereferenced at line 1530, column 21.

libavcodec/mpegvideo.c:1515:1: start of procedure ff_MPV_frame_end()
1513. /* generic function for encode/decode called after a
1514.  * frame has been coded/decoded. */
1515. void ff_MPV_frame_end(MpegEncContext *s)
      ^
1516. {
1517.     int i;

libavcodec/mpegvideo.c:1520:9: Taking false branch
1518.     /* redraw edges for the frame if decoding didn't complete */
1519.     // just to make sure that all data is rendered.
1520.     if (CONFIG_MPEG_XVMC_DECODER && s->avctx->xvmc_acceleration) {
              ^
1521.         ff_xvmc_field_end(s);
1522.    } else if ((s->error_count || s->encoding) &&

libavcodec/mpegvideo.c:1522:16: Taking false branch
1520.     if (CONFIG_MPEG_XVMC_DECODER && s->avctx->xvmc_acceleration) {
1521.         ff_xvmc_field_end(s);
1522.    } else if ((s->error_count || s->encoding) &&
                     ^
1523.               !s->avctx->hwaccel &&
1524.               !(s->avctx->codec->capabilities & CODEC_CAP_HWACCEL_VDPAU) &&

libavcodec/mpegvideo.c:1522:34: Taking true branch
1520.     if (CONFIG_MPEG_XVMC_DECODER && s->avctx->xvmc_acceleration) {
1521.         ff_xvmc_field_end(s);
1522.    } else if ((s->error_count || s->encoding) &&
                                       ^
1523.               !s->avctx->hwaccel &&
1524.               !(s->avctx->codec->capabilities & CODEC_CAP_HWACCEL_VDPAU) &&

libavcodec/mpegvideo.c:1523:16: Taking true branch
1521.         ff_xvmc_field_end(s);
1522.    } else if ((s->error_count || s->encoding) &&
1523.               !s->avctx->hwaccel &&
                     ^
1524.               !(s->avctx->codec->capabilities & CODEC_CAP_HWACCEL_VDPAU) &&
1525.               s->unrestricted_mv &&

libavcodec/mpegvideo.c:1524:17: Taking true branch
1522.    } else if ((s->error_count || s->encoding) &&
1523.               !s->avctx->hwaccel &&
1524.               !(s->avctx->codec->capabilities & CODEC_CAP_HWACCEL_VDPAU) &&
                      ^
1525.               s->unrestricted_mv &&
1526.               s->current_picture.f.reference &&

libavcodec/mpegvideo.c:1525:15: Taking true branch
1523.               !s->avctx->hwaccel &&
1524.               !(s->avctx->codec->capabilities & CODEC_CAP_HWACCEL_VDPAU) &&
1525.               s->unrestricted_mv &&
                    ^
1526.               s->current_picture.f.reference &&
1527.               !s->intra_only &&

libavcodec/mpegvideo.c:1526:15: Taking true branch
1524.               !(s->avctx->codec->capabilities & CODEC_CAP_HWACCEL_VDPAU) &&
1525.               s->unrestricted_mv &&
1526.               s->current_picture.f.reference &&
                    ^
1527.               !s->intra_only &&
1528.               !(s->flags & CODEC_FLAG_EMU_EDGE)) {

libavcodec/mpegvideo.c:1527:16: Taking true branch
1525.               s->unrestricted_mv &&
1526.               s->current_picture.f.reference &&
1527.               !s->intra_only &&
                     ^
1528.               !(s->flags & CODEC_FLAG_EMU_EDGE)) {
1529.        const AVPixFmtDescriptor *desc = av_pix_fmt_desc_get(s->avctx->pix_fmt);

libavcodec/mpegvideo.c:1528:17: Taking true branch
1526.               s->current_picture.f.reference &&
1527.               !s->intra_only &&
1528.               !(s->flags & CODEC_FLAG_EMU_EDGE)) {
                      ^
1529.        const AVPixFmtDescriptor *desc = av_pix_fmt_desc_get(s->avctx->pix_fmt);
1530.        int hshift = desc->log2_chroma_w;

libavcodec/mpegvideo.c:1529:8: 
1527.               !s->intra_only &&
1528.               !(s->flags & CODEC_FLAG_EMU_EDGE)) {
1529.        const AVPixFmtDescriptor *desc = av_pix_fmt_desc_get(s->avctx->pix_fmt);
             ^
1530.        int hshift = desc->log2_chroma_w;
1531.        int vshift = desc->log2_chroma_h;

libavutil/pixdesc.c:1433:1: start of procedure av_pix_fmt_desc_get()
  1431. }
  1432. 
  1433. const AVPixFmtDescriptor *av_pix_fmt_desc_get(enum AVPixelFormat pix_fmt)
        ^
  1434. {
  1435.     if (pix_fmt < 0 || pix_fmt >= AV_PIX_FMT_NB)

libavutil/pixdesc.c:1435:9: Taking false branch
  1433. const AVPixFmtDescriptor *av_pix_fmt_desc_get(enum AVPixelFormat pix_fmt)
  1434. {
  1435.     if (pix_fmt < 0 || pix_fmt >= AV_PIX_FMT_NB)
                ^
  1436.         return NULL;
  1437.     return &av_pix_fmt_descriptors[pix_fmt];

libavutil/pixdesc.c:1435:24: Taking true branch
  1433. const AVPixFmtDescriptor *av_pix_fmt_desc_get(enum AVPixelFormat pix_fmt)
  1434. {
  1435.     if (pix_fmt < 0 || pix_fmt >= AV_PIX_FMT_NB)
                               ^
  1436.         return NULL;
  1437.     return &av_pix_fmt_descriptors[pix_fmt];

libavutil/pixdesc.c:1436:9: 
  1434. {
  1435.     if (pix_fmt < 0 || pix_fmt >= AV_PIX_FMT_NB)
  1436.         return NULL;
                ^
  1437.     return &av_pix_fmt_descriptors[pix_fmt];
  1438. }

libavutil/pixdesc.c:1438:1: return from a call to av_pix_fmt_desc_get
  1436.         return NULL;
  1437.     return &av_pix_fmt_descriptors[pix_fmt];
  1438. }
        ^
  1439. 
  1440. const AVPixFmtDescriptor *av_pix_fmt_desc_next(const AVPixFmtDescriptor *prev)

libavcodec/mpegvideo.c:1530:8: 
1528.               !(s->flags & CODEC_FLAG_EMU_EDGE)) {
1529.        const AVPixFmtDescriptor *desc = av_pix_fmt_desc_get(s->avctx->pix_fmt);
1530.        int hshift = desc->log2_chroma_w;
             ^
1531.        int vshift = desc->log2_chroma_h;
1532.        s->dsp.draw_edges(s->current_picture.f.data[0], s->linesize,
