screenshots: check for AVFrame csp support

Apparently, libav stable is old enough to not have these fields.

old-configure

@@ -813,6 +813,12 @@ api_statement_check \
     libavutil/frame.h \
     'av_frame_get_metadata(NULL)'
 
+api_statement_check \
+    "libavutil AVFrame colorspace information" \
+    HAVE_AVFRAME_CSP \
+    libavutil/frame.h \
+    'AVFrame frame; frame.color_primaries = frame.color_trc = 0;'
+
 api_statement_check \
     "libavutil AVFrame skip samples metadata" \
     HAVE_AVFRAME_SKIP_SAMPLES \

video/image_writer.c

@@ -133,10 +133,12 @@ static int write_lavc(struct image_writer_ctx *ctx, mp_image_t *image, FILE *fp)
     pic->format = avctx->pix_fmt;
     pic->width = avctx->width;
     pic->height = avctx->height;
+#if HAVE_AVFRAME_CSP
     if (ctx->opts->tag_csp) {
         pic->color_primaries = mp_csp_prim_to_avcol_pri(image->params.primaries);
         pic->color_trc = mp_csp_trc_to_avcol_trc(image->params.gamma);
     }
+#endif
     int ret = avcodec_encode_video2(avctx, &pkt, pic, &got_output);
     if (ret < 0)
         goto error_exit;

wscript

@@ -462,6 +462,13 @@ Libav libraries ({0}). Aborting.".format(" ".join(libav_pkg_config_checks))
         'func': check_statement('libavutil/frame.h',
                                 'enum AVFrameSideDataType type = AV_FRAME_DATA_SKIP_SAMPLES',
                                 use='libav')
+    }, {
+        'name': 'avframe-csp',
+        'desc': 'libavutil AVFrame colorspace information',
+        'func': check_statement('libavutil/frame.h',
+                                'AVFrame frame;'
+                                'frame.color_primaries = frame.color_trc = 0;',
+                                use='libav')
     }
 ]