diff --git a/libavcodec/h264.c b/libavcodec/h264.c
index a4892ac902616a45650774cf9232a21f750198a0..a3343da6e4ba37e3fcbf920b5ee944159fb88042 100644
--- a/libavcodec/h264.c
+++ b/libavcodec/h264.c
@@ -1224,7 +1224,7 @@ static int decode_update_thread_context(AVCodecContext *dst, const AVCodecContex
     int inited = s->context_initialized, err;
     int i;
 
-    if(dst == src || !s1->context_initialized) return 0;
+    if(dst == src) return 0;
 
     err = ff_mpeg_update_thread_context(dst, src);
     if(err) return err;
@@ -1240,12 +1240,19 @@ static int decode_update_thread_context(AVCodecContext *dst, const AVCodecContex
         memcpy(&h->s + 1, &h1->s + 1, sizeof(H264Context) - sizeof(MpegEncContext)); //copy all fields after MpegEnc
         memset(h->sps_buffers, 0, sizeof(h->sps_buffers));
         memset(h->pps_buffers, 0, sizeof(h->pps_buffers));
+
+        if (s1->context_initialized) {
         if (ff_h264_alloc_tables(h) < 0) {
             av_log(dst, AV_LOG_ERROR, "Could not allocate memory for h264\n");
             return AVERROR(ENOMEM);
         }
         context_init(h);
 
+        // frame_start may not be called for the next thread (if it's decoding a bottom field)
+        // so this has to be allocated here
+        h->s.obmc_scratchpad = av_malloc(16*6*s->linesize);
+        }
+
         for(i=0; i<2; i++){
             h->rbsp_buffer[i] = NULL;
             h->rbsp_buffer_size[i] = 0;
@@ -1253,10 +1260,6 @@ static int decode_update_thread_context(AVCodecContext *dst, const AVCodecContex
 
         h->thread_context[0] = h;
 
-        // frame_start may not be called for the next thread (if it's decoding a bottom field)
-        // so this has to be allocated here
-        h->s.obmc_scratchpad = av_malloc(16*6*s->linesize);
-
         s->dsp.clear_blocks(h->mb);
         s->dsp.clear_blocks(h->mb+(24*16<<h->pixel_shift));
     }
diff --git a/libavcodec/mpegvideo.c b/libavcodec/mpegvideo.c
index 04c149a99bfc09866c0cd0dfec88f54fb3953827..f197bd78a26cbd959024166fa4b4c4c054c61bc7 100644
--- a/libavcodec/mpegvideo.c
+++ b/libavcodec/mpegvideo.c
@@ -531,7 +531,7 @@ int ff_mpeg_update_thread_context(AVCodecContext *dst,
 {
     MpegEncContext *s = dst->priv_data, *s1 = src->priv_data;
 
-    if (dst == src || !s1->context_initialized)
+    if (dst == src)
         return 0;
 
     // FIXME can parameters change on I-frames?
@@ -540,12 +540,14 @@ int ff_mpeg_update_thread_context(AVCodecContext *dst,
         memcpy(s, s1, sizeof(MpegEncContext));
 
         s->avctx                 = dst;
-        s->picture_range_start  += MAX_PICTURE_COUNT;
-        s->picture_range_end    += MAX_PICTURE_COUNT;
         s->bitstream_buffer      = NULL;
         s->bitstream_buffer_size = s->allocated_bitstream_buffer_size = 0;
 
-        MPV_common_init(s);
+        if (s1->context_initialized){
+            s->picture_range_start  += MAX_PICTURE_COUNT;
+            s->picture_range_end    += MAX_PICTURE_COUNT;
+            MPV_common_init(s);
+        }
     }
 
     s->avctx->coded_height  = s1->avctx->coded_height;