avcodec/mpegvideo: Don't initialize H264Chroma ctx unnecessarily

It is only used by the decoders' lowres code, so only initialize
it for decoders.
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>

configure

@@ -2754,8 +2754,8 @@ me_cmp_select="idctdsp"
 mpeg_er_select="error_resilience"
 mpegaudio_select="mpegaudiodsp mpegaudioheader"
 mpegaudiodsp_select="dct"
-mpegvideo_select="blockdsp h264chroma hpeldsp idctdsp videodsp"
-mpegvideodec_select="mpegvideo mpeg_er"
+mpegvideo_select="blockdsp hpeldsp idctdsp videodsp"
+mpegvideodec_select="h264chroma mpegvideo mpeg_er"
 mpegvideoenc_select="aandcttables fdctdsp me_cmp mpegvideo pixblockdsp qpeldsp"
 msmpeg4dec_select="h263_decoder"
 msmpeg4enc_select="h263_encoder"

libavcodec/mpegvideo.c

@@ -34,7 +34,6 @@
 
 #include "avcodec.h"
 #include "blockdsp.h"
-#include "h264chroma.h"
 #include "idctdsp.h"
 #include "mathops.h"
 #include "mpeg_er.h"
@@ -275,7 +274,6 @@ static void gray8(uint8_t *dst, const uint8_t *src, ptrdiff_t linesize, int h)
 static av_cold int dct_init(MpegEncContext *s)
 {
     ff_blockdsp_init(&s->bdsp);
-    ff_h264chroma_init(&s->h264chroma, 8); //for lowres
     ff_hpeldsp_init(&s->hdsp, s->avctx->flags);
     ff_videodsp_init(&s->vdsp, s->avctx->bits_per_raw_sample);
 

libavcodec/mpegvideo_dec.c

@@ -51,6 +51,8 @@ void ff_mpv_decode_init(MpegEncContext *s, AVCodecContext *avctx)
 
     /* convert fourcc to upper case */
     s->codec_tag       = ff_toupper4(avctx->codec_tag);
+
+    ff_h264chroma_init(&s->h264chroma, 8); //for lowres
 }
 
 int ff_mpeg_update_thread_context(AVCodecContext *dst,
@@ -83,6 +85,7 @@ int ff_mpeg_update_thread_context(AVCodecContext *dst,
                 memset(s, 0, sizeof(*s));
                 s->avctx = dst;
                 s->private_ctx = private_ctx;
+                memcpy(&s->h264chroma, &s1->h264chroma, sizeof(s->h264chroma));
                 return err;
             }
         }