From b83d8be6bff7d645469a623aee0b380541da15cf Mon Sep 17 00:00:00 2001
From: Michael Niedermayer <michael@niedermayer.cc>
Date: Thu, 24 Dec 2015 21:46:15 +0100
Subject: [PATCH] swscale/utils: Fix intermediate format for cascaded alpha
 downscaling

Fixes Ticket4926

Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
---
 libswscale/utils.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/libswscale/utils.c b/libswscale/utils.c
index db937b160f..e5593af4dd 100644
--- a/libswscale/utils.c
+++ b/libswscale/utils.c
@@ -1803,6 +1803,9 @@ fail: // FIXME replace things by appropriate error codes
         int tmpH = sqrt(srcH * (int64_t)dstH);
         enum AVPixelFormat tmpFormat = AV_PIX_FMT_YUV420P;
 
+        if (isALPHA(srcFormat))
+            tmpFormat = AV_PIX_FMT_YUVA420P;
+
         if (srcW*(int64_t)srcH <= 4LL*dstW*dstH)
             return AVERROR(EINVAL);