The mpeg4 video, H264 and VC-1 parser hold a directly or indirectly
a MpegEncContext in their private context. Since they do not call the
common mpegvideo init function slice_context_count has explicitly set
to 1.
Prevents a null pointer dereference in the h264 parser and fixes
buf 193.
---
 libavcodec/h264_parser.c       |    1 +
 libavcodec/mpeg4video_parser.c |    1 +
 libavcodec/vc1_parser.c        |    8 ++++++++
 3 files changed, 10 insertions(+), 0 deletions(-)

diff --git a/libavcodec/h264_parser.c b/libavcodec/h264_parser.c
index 826c17a..bcaa04a 100644
--- a/libavcodec/h264_parser.c
+++ b/libavcodec/h264_parser.c
@@ -330,6 +330,7 @@ static int init(AVCodecParserContext *s)
 {
     H264Context *h = s->priv_data;
     h->thread_context[0] = h;
+    h->s.slice_context_count = 1;
     return 0;
 }
 
diff --git a/libavcodec/mpeg4video_parser.c b/libavcodec/mpeg4video_parser.c
index 162bc1d..89bbf34 100644
--- a/libavcodec/mpeg4video_parser.c
+++ b/libavcodec/mpeg4video_parser.c
@@ -99,6 +99,7 @@ static av_cold int mpeg4video_parse_init(AVCodecParserContext 
*s)
     if (!pc->enc)
         return -1;
     pc->first_picture = 1;
+    pc->enc->slice_context_count = 1;
     return 0;
 }
 
diff --git a/libavcodec/vc1_parser.c b/libavcodec/vc1_parser.c
index e6243d9..0cc5ea0 100644
--- a/libavcodec/vc1_parser.c
+++ b/libavcodec/vc1_parser.c
@@ -184,9 +184,17 @@ static int vc1_split(AVCodecContext *avctx,
     return 0;
 }
 
+static int vc1_parse_init(AVCodecParserContext *s)
+{
+    VC1ParseContext *vpc = s->priv_data;
+    vpc->v.s.slice_context_count = 1;
+    return 0;
+}
+
 AVCodecParser ff_vc1_parser = {
     .codec_ids      = { CODEC_ID_VC1 },
     .priv_data_size = sizeof(VC1ParseContext),
+    .parser_init    = vc1_parse_init,
     .parser_parse   = vc1_parse,
     .parser_close   = ff_parse1_close,
     .split          = vc1_split,
-- 
1.7.8.2

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