Merge commit '6b3ff6f91a535d6383f41ca7bdf760165dcb6015'

* commit '6b3ff6f91a535d6383f41ca7bdf760165dcb6015':
  swscale: provide a default scaler if none is set

Conflicts:
	libswscale/utils.c

The default is left at bicubic until someone has compared the scalers
properly speed and quality wise.

Merged-by: Michael Niedermayer <michaelni@gmx.at>

libswscale/utils.c

@@ -1155,8 +1155,19 @@ av_cold int sws_init_context(SwsContext *c, SwsFilter *srcFilter,
                  SWS_SINC          |
                  SWS_SPLINE        |
                  SWS_BICUBLIN);
-    if (!i || (i & (i - 1))) {
-        av_log(c, AV_LOG_ERROR, "Exactly one scaler algorithm must be chosen, got %X\n", i);
+
+    /* provide a default scaler if not set by caller */
+    if (!i) {
+        if (dstW < srcW && dstH < srcH)
+            flags |= SWS_BICUBIC;
+        else if (dstW > srcW && dstH > srcH)
+            flags |= SWS_BICUBIC;
+        else
+            flags |= SWS_BICUBIC;
+        c->flags = flags;
+    } else if (i & (i - 1)) {
+        av_log(c, AV_LOG_ERROR,
+               "Exactly one scaler algorithm must be chosen, got %X\n", i);
         return AVERROR(EINVAL);
     }
     /* sanity check */