From 4b70bba57ec9d61282e8b2b427d738dd44415652 Mon Sep 17 00:00:00 2001
From: Paul B Mahol <onemda@gmail.com>
Date: Fri, 4 May 2012 10:24:39 +0000
Subject: [PATCH] zerocodec: check if there is previous frame

Fixes crash in bug #1219.

Signed-off-by: Paul B Mahol <onemda@gmail.com>
---
 libavcodec/zerocodec.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/libavcodec/zerocodec.c b/libavcodec/zerocodec.c
index 02e37bc0e7..4944a3e486 100644
--- a/libavcodec/zerocodec.c
+++ b/libavcodec/zerocodec.c
@@ -65,6 +65,10 @@ static int zerocodec_decode_frame(AVCodecContext *avctx, void *data,
         pic->key_frame = 1;
         pic->pict_type = AV_PICTURE_TYPE_I;
     } else {
+        if (prev == NULL) {
+            av_log(avctx, AV_LOG_ERROR, "No previous frame!\n");
+            return AVERROR_INVALIDDATA;
+        }
         pic->key_frame = 0;
         pic->pict_type = AV_PICTURE_TYPE_P;
     }