Re: [FFmpeg-devel] [PATCH 5/8] avcodec/mpeg12dec: Don't initialize IDCT more than once

[Andreas Rheinhardt <andreas.rheinhardt@outlook.com>]

Andreas Rheinhardt:
> Before 998c9f15d1ca8c7489775ebcca51623b915988f1, the IDCTDSPContext
> has only been initialized in ff_mpv_common_init() which is deferred
> until immediately before decoding a picture; to nevertheless parse
> the quant matrices in sequence headers or quant matrix extensions,
> a dummy (identity) permutation has been stored in the codec's init
> function; after ff_mpv_common_init() which could change the permutation
> the matrices were repermutated.
> 
> Yet since said commit, the IDCTDSPContext is initialized during init
> and does not change afterwards (unless the user forces different CPU
> flags), so there is no need to reinitialize it; the repermutation code
> can be removed as well.
> 
> Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>
> ---
>  libavcodec/mpeg12dec.c | 26 --------------------------
>  1 file changed, 26 deletions(-)
> 
> diff --git a/libavcodec/mpeg12dec.c b/libavcodec/mpeg12dec.c
> index 92ef6944fa..d2dbcd5b61 100644
> --- a/libavcodec/mpeg12dec.c
> +++ b/libavcodec/mpeg12dec.c
> @@ -1057,8 +1057,6 @@ static av_cold int mpeg_decode_init(AVCodecContext *avctx)
>          avctx->coded_width = avctx->coded_height = 0; // do not trust dimensions from input
>      ff_mpv_decode_init(s2, avctx);
>  
> -    /* we need some permutation to store matrices,
> -     * until the decoder sets the real permutation. */
>      ff_mpv_idct_init(s2);
>      ff_mpeg12_init_vlcs();
>  
> @@ -1093,18 +1091,6 @@ static int mpeg_decode_update_thread_context(AVCodecContext *avctx,
>  }
>  #endif
>  
> -static void quant_matrix_rebuild(uint16_t *matrix, const uint8_t *old_perm,
> -                                 const uint8_t *new_perm)
> -{
> -    uint16_t temp_matrix[64];
> -    int i;
> -
> -    memcpy(temp_matrix, matrix, 64 * sizeof(uint16_t));
> -
> -    for (i = 0; i < 64; i++)
> -        matrix[new_perm[i]] = temp_matrix[old_perm[i]];
> -}
> -
>  static const enum AVPixelFormat mpeg1_hwaccel_pixfmt_list_420[] = {
>  #if CONFIG_MPEG1_NVDEC_HWACCEL
>      AV_PIX_FMT_CUDA,
> @@ -1177,7 +1163,6 @@ static int mpeg_decode_postinit(AVCodecContext *avctx)
>  {
>      Mpeg1Context *s1  = avctx->priv_data;
>      MpegEncContext *s = &s1->mpeg_enc_ctx;
> -    uint8_t old_permutation[64];
>      int ret;
>  
>      if (avctx->codec_id == AV_CODEC_ID_MPEG1VIDEO) {
> @@ -1297,19 +1282,9 @@ FF_ENABLE_DEPRECATION_WARNINGS
>  
>          avctx->pix_fmt = mpeg_get_pixelformat(avctx);
>  
> -        /* Quantization matrices may need reordering
> -         * if DCT permutation is changed. */
> -        memcpy(old_permutation, s->idsp.idct_permutation, 64 * sizeof(uint8_t));
> -
> -        ff_mpv_idct_init(s);
>          if ((ret = ff_mpv_common_init(s)) < 0)
>              return ret;
>  
> -        quant_matrix_rebuild(s->intra_matrix,        old_permutation, s->idsp.idct_permutation);
> -        quant_matrix_rebuild(s->inter_matrix,        old_permutation, s->idsp.idct_permutation);
> -        quant_matrix_rebuild(s->chroma_intra_matrix, old_permutation, s->idsp.idct_permutation);
> -        quant_matrix_rebuild(s->chroma_inter_matrix, old_permutation, s->idsp.idct_permutation);
> -
>          s1->mpeg_enc_ctx_allocated = 1;
>      }
>      return 0;
> @@ -2169,7 +2144,6 @@ static int vcr2_init_sequence(AVCodecContext *avctx)
>  
>      avctx->pix_fmt = mpeg_get_pixelformat(avctx);
>  
> -    ff_mpv_idct_init(s);
>      if ((ret = ff_mpv_common_init(s)) < 0)
>          return ret;
>      s1->mpeg_enc_ctx_allocated = 1;

Will apply patches 5-8 tomorrow unless there are objections.

- Andreas

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