uninitalized variables fix by (Gildas Bazin <gbazin at altern dot org>)

and some related cleanup by me

Originally committed as revision 2677 to svn://svn.ffmpeg.org/ffmpeg/trunk

ffmpeg.c

@@ -483,7 +483,7 @@ static void do_video_out(AVFormatContext *s,
     int nb_frames, i, ret;
     AVPicture *final_picture, *formatted_picture;
     AVPicture picture_format_temp, picture_crop_temp;
-    static uint8_t *video_buffer;
+    static uint8_t *video_buffer= NULL;
     uint8_t *buf = NULL, *buf1 = NULL;
     AVCodecContext *enc, *dec;
     enum PixelFormat target_pixfmt;

libavcodec/mpeg12.c

@@ -1737,6 +1737,7 @@ static int mpeg_decode_init(AVCodecContext *avctx)
 {
     Mpeg1Context *s = avctx->priv_data;
     
+    s->mpeg_enc_ctx.avctx= avctx;
     s->mpeg_enc_ctx.flags= avctx->flags;
     common_init(&s->mpeg_enc_ctx);
     init_vlcs();
@@ -2372,7 +2373,6 @@ static int mpeg1_decode_sequence(AVCodecContext *avctx,
         s->width = width;
         s->height = height;
         avctx->has_b_frames= 1;
-        s->avctx = avctx;
         avctx->width = width;
         avctx->height = height;
         av_reduce(
@@ -2474,7 +2474,6 @@ static int vcr2_init_sequence(AVCodecContext *avctx)
     s->height = avctx->height;
     avctx->has_b_frames= 0; //true?
     s->low_delay= 1;
-    s->avctx = avctx;
 
     //get_format() or set_video(width,height,aspect,pix_fmt);
     //until then pix_fmt may be changed right after codec init