lavc, lavfi: fix counting number of planes in AVBufferRef wrappers

Number of planes is not always equal to the number of components even
for formats marked with PIX_FMT_PLANAR -- e.g. NV12 has three components
in two planes.

libavcodec/utils.c

@@ -660,11 +660,11 @@ do {                                                                    \
         if (avctx->codec_type == AVMEDIA_TYPE_VIDEO) {
             const AVPixFmtDescriptor *desc = av_pix_fmt_desc_get(frame->format);
 
-            if (!desc) {
+            planes = av_pix_fmt_count_planes(frame->format);
+            if (!desc || planes <= 0) {
                 ret = AVERROR(EINVAL);
                 goto fail;
             }
-            planes = (desc->flags & PIX_FMT_PLANAR) ? desc->nb_components : 1;
 
             for (i = 0; i < planes; i++) {
                 int v_shift    = (i == 1 || i == 2) ? desc->log2_chroma_h : 0;

libavfilter/buffersrc.c

@@ -186,11 +186,11 @@ do {                                                                    \
     if (ctx->outputs[0]->type  == AVMEDIA_TYPE_VIDEO) {
         const AVPixFmtDescriptor *desc = av_pix_fmt_desc_get(frame->format);
 
-        if (!desc) {
+        planes = av_pix_fmt_count_planes(frame->format);
+        if (!desc || planes <= 0) {
             ret = AVERROR(EINVAL);
             goto fail;
         }
-        planes = (desc->flags & PIX_FMT_PLANAR) ? desc->nb_components : 1;
 
         for (i = 0; i < planes; i++) {
             int v_shift    = (i == 1 || i == 2) ? desc->log2_chroma_w : 0;