avcodec: remove AVCodecContext->metadata

This field was only ever set and freed from avcodec, and not otherwise
used. However, because frames are refcounted now, avcodec cannot make any
assumptions about the lifetime of the frame metadata, which can result in
double-frees or leaked memory.
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavcodec/avcodec.h

@@ -2792,13 +2792,6 @@ typedef struct AVCodecContext {
     int64_t pts_correction_last_pts;       /// PTS of the last frame
     int64_t pts_correction_last_dts;       /// DTS of the last frame
 
-    /**
-     * Current frame metadata.
-     * - decoding: maintained and used by libavcodec, not intended to be used by user apps
-     * - encoding: unused
-     */
-    AVDictionary *metadata;
-
     /**
      * Character encoding of the input subtitles file.
      * - decoding: set by user

libavcodec/utils.c

@@ -1862,7 +1862,6 @@ static int add_metadata_from_side_data(AVCodecContext *avctx, AVFrame *frame)
     const uint8_t *side_metadata;
     const uint8_t *end;
 
-    av_dict_free(&avctx->metadata);
     side_metadata = av_packet_get_side_data(avctx->pkt,
                                             AV_PKT_DATA_STRINGS_METADATA, &size);
     if (!side_metadata)
@@ -1877,7 +1876,6 @@ static int add_metadata_from_side_data(AVCodecContext *avctx, AVFrame *frame)
         side_metadata = val + strlen(val) + 1;
     }
 end:
-    avctx->metadata = av_frame_get_metadata(frame);
     return ret;
 }
 
@@ -2298,7 +2296,6 @@ av_cold int avcodec_close(AVCodecContext *avctx)
             av_buffer_pool_uninit(&pool->pools[i]);
         av_freep(&avctx->internal->pool);
         av_freep(&avctx->internal);
-        av_dict_free(&avctx->metadata);
     }
 
     if (avctx->priv_data && avctx->codec && avctx->codec->priv_class)