avcodec/avcodec: Move initializing frame-thrd encoder to encode_preinit

Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>

libavcodec/avcodec.c

@@ -283,12 +283,6 @@ FF_ENABLE_DEPRECATION_WARNINGS
     if (ret < 0)
         goto free_and_end;
 
-    if (CONFIG_FRAME_THREAD_ENCODER && av_codec_is_encoder(avctx->codec)) {
-        ret = ff_frame_thread_encoder_init(avctx);
-        if (ret < 0)
-            goto free_and_end;
-    }
-
     if (HAVE_THREADS
         && !(avci->frame_thread_encoder && (avctx->active_thread_type&FF_THREAD_FRAME))) {
         /* Frame-threaded decoders call FFCodec.init for their child contexts. */

libavcodec/encode.c

@@ -668,6 +668,12 @@ int ff_encode_preinit(AVCodecContext *avctx)
             return AVERROR(ENOMEM);
     }
 
+    if (CONFIG_FRAME_THREAD_ENCODER) {
+        ret = ff_frame_thread_encoder_init(avctx);
+        if (ret < 0)
+            return ret;
+    }
+
     return 0;
 }