avcodec/decode: sync initial_pict_type and intra_only_flag with thread worker's avctx

Regression since 5acbdd2264, which removed
setting both values from PerThreadContext.
Given the pthread code calls ff_decode_receive_frame_internal() on the frame,
any value set before it will be overwritten, so instead sync each thread's
DecodeContext and let ff_decode_receive_frame_internal() handle these values.

Fixes issue #20534.

Signed-off-by: James Almer <jamrial@gmail.com>
(cherry picked from commit 26f4230082)

libavcodec/decode.c

@@ -2235,6 +2235,8 @@ void ff_decode_internal_sync(AVCodecContext *dst, const AVCodecContext *src)
     const DecodeContext *src_dc = decode_ctx(src->internal);
     DecodeContext *dst_dc = decode_ctx(dst->internal);
 
+    dst_dc->initial_pict_type = src_dc->initial_pict_type;
+    dst_dc->intra_only_flag   = src_dc->intra_only_flag;
     av_refstruct_replace(&dst_dc->lcevc, src_dc->lcevc);
 }
 

libavcodec/pthread_frame.c

@@ -115,10 +115,6 @@ typedef struct PerThreadContext {
     int hwaccel_threadsafe;
 
     atomic_int debug_threads;       ///< Set if the FF_DEBUG_THREADS option is set.
-
-    /// The following two fields have the same semantics as the DecodeContext field
-    int intra_only_flag;
-    enum AVPictureType initial_pict_type;
 } PerThreadContext;
 
 /**
@@ -820,13 +816,6 @@ static av_cold int init_thread(PerThreadContext *p, int *threads_to_free,
     AVCodecContext *copy;
     int err;
 
-    p->initial_pict_type = AV_PICTURE_TYPE_NONE;
-    if (avctx->codec_descriptor->props & AV_CODEC_PROP_INTRA_ONLY) {
-        p->intra_only_flag = AV_FRAME_FLAG_KEY;
-        if (avctx->codec_type == AVMEDIA_TYPE_VIDEO)
-            p->initial_pict_type = AV_PICTURE_TYPE_I;
-    }
-
     atomic_init(&p->state, STATE_INPUT_READY);
 
     copy = av_memdup(avctx, sizeof(*avctx));