From aec340c533293d6230573aaf3fe22a74e5454b99 Mon Sep 17 00:00:00 2001
From: Michael Niedermayer <michael@niedermayer.cc>
Date: Thu, 10 Sep 2015 16:06:14 +0200
Subject: [PATCH] avcodec/bmp: Analyze BGRA files alpha channel to choose pixel
 format

BGRA BMPs commonly do contain an all transparent alpha channel

Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
---
 libavcodec/bmp.c | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/libavcodec/bmp.c b/libavcodec/bmp.c
index 42270da6e7..3019d01016 100644
--- a/libavcodec/bmp.c
+++ b/libavcodec/bmp.c
@@ -337,6 +337,20 @@ static int bmp_decode_frame(AVCodecContext *avctx,
             return AVERROR_INVALIDDATA;
         }
     }
+    if (avctx->pix_fmt == AV_PIX_FMT_BGRA) {
+        for (i = 0; i < avctx->height; i++) {
+            int j;
+            uint8_t *ptr = p->data[0] + p->linesize[0]*i + 3;
+            for (j = 0; j < avctx->width; j++) {
+                if (ptr[4*j])
+                    break;
+            }
+            if (j < avctx->width)
+                break;
+        }
+        if (i == avctx->height)
+            avctx->pix_fmt = p->format = AV_PIX_FMT_BGR0;
+    }
 
     *got_frame = 1;