vf_scale: use the pixfmt descriptor API

Avoid using AV_PIX_FMT_NB, since that hardcodes the number of pixel
formats into lavfi and will break when a shared lavu is updated, adding
new pixel formats.

libavfilter/vf_scale.c

@@ -120,25 +120,31 @@ static int query_formats(AVFilterContext *ctx)
     int ret;
 
     if (ctx->inputs[0]) {
+        const AVPixFmtDescriptor *desc = NULL;
         formats = NULL;
-        for (pix_fmt = 0; pix_fmt < AV_PIX_FMT_NB; pix_fmt++)
+        while ((desc = av_pix_fmt_desc_next(desc))) {
+            pix_fmt = av_pix_fmt_desc_get_id(desc);
             if ((sws_isSupportedInput(pix_fmt) ||
                  sws_isSupportedEndiannessConversion(pix_fmt))
                 && (ret = ff_add_format(&formats, pix_fmt)) < 0) {
                 ff_formats_unref(&formats);
                 return ret;
             }
+        }
         ff_formats_ref(formats, &ctx->inputs[0]->out_formats);
     }
     if (ctx->outputs[0]) {
+        const AVPixFmtDescriptor *desc = NULL;
         formats = NULL;
-        for (pix_fmt = 0; pix_fmt < AV_PIX_FMT_NB; pix_fmt++)
+        while ((desc = av_pix_fmt_desc_next(desc))) {
+            pix_fmt = av_pix_fmt_desc_get_id(desc);
             if ((sws_isSupportedOutput(pix_fmt) ||
                  sws_isSupportedEndiannessConversion(pix_fmt))
                 && (ret = ff_add_format(&formats, pix_fmt)) < 0) {
                 ff_formats_unref(&formats);
                 return ret;
             }
+        }
         ff_formats_ref(formats, &ctx->outputs[0]->in_formats);
     }