Re: [FFmpeg-devel] [PATCH] avcodec/h264dec: Remove dead function

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

Kieran Kunhya:
> On Wed, 15 Mar 2023 at 17:17, Andreas Rheinhardt <
> andreas.rheinhardt@outlook.com> wrote:
> 
>> Andreas Rheinhardt:
>>> The H.264 decoder does not support draw_horiz_band (it does not have
>>> the AV_CODEC_CAP_DRAW_HORIZ_BAND), making ff_h264_draw_horiz_band()
>>> practically dead.
>>>
>>> Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>
>>> ---
>>>  libavcodec/dxva2_h264.c |  7 +------
>>>  libavcodec/h264_slice.c |  2 --
>>>  libavcodec/h264dec.c    | 35 -----------------------------------
>>>  libavcodec/h264dec.h    |  2 --
>>>  libavcodec/vaapi_h264.c | 11 +----------
>>>  libavcodec/vdpau_h264.c |  2 --
>>>  6 files changed, 2 insertions(+), 57 deletions(-)
>>>
>>> diff --git a/libavcodec/dxva2_h264.c b/libavcodec/dxva2_h264.c
>>> index 6300b1418d..26e18a71b0 100644
>>> --- a/libavcodec/dxva2_h264.c
>>> +++ b/libavcodec/dxva2_h264.c
>>> @@ -499,20 +499,15 @@ static int dxva2_h264_decode_slice(AVCodecContext
>> *avctx,
>>>  static int dxva2_h264_end_frame(AVCodecContext *avctx)
>>>  {
>>>      H264Context *h = avctx->priv_data;
>>> -    H264SliceContext *sl = &h->slice_ctx[0];
>>>      struct dxva2_picture_context *ctx_pic =
>>>          h->cur_pic_ptr->hwaccel_picture_private;
>>> -    int ret;
>>>
>>>      if (ctx_pic->slice_count <= 0 || ctx_pic->bitstream_size <= 0)
>>>          return -1;
>>> -    ret = ff_dxva2_common_end_frame(avctx, h->cur_pic_ptr->f,
>>> +    return ff_dxva2_common_end_frame(avctx, h->cur_pic_ptr->f,
>>>                                      &ctx_pic->pp, sizeof(ctx_pic->pp),
>>>                                      &ctx_pic->qm, sizeof(ctx_pic->qm),
>>>                                      commit_bitstream_and_slice_buffer);
>>> -    if (!ret)
>>> -        ff_h264_draw_horiz_band(h, sl, 0, h->avctx->height);
>>> -    return ret;
>>>  }
>>>
>>>  #if CONFIG_H264_DXVA2_HWACCEL
>>> diff --git a/libavcodec/h264_slice.c b/libavcodec/h264_slice.c
>>> index 7767e16cf1..912f1ea9c7 100644
>>> --- a/libavcodec/h264_slice.c
>>> +++ b/libavcodec/h264_slice.c
>>> @@ -2490,8 +2490,6 @@ static void decode_finish_row(const H264Context
>> *h, H264SliceContext *sl)
>>>          top    = 0;
>>>      }
>>>
>>> -    ff_h264_draw_horiz_band(h, sl, top, height);
>>> -
>>>      if (h->droppable || h->er.error_occurred)
>>>          return;
>>>
>>> diff --git a/libavcodec/h264dec.c b/libavcodec/h264dec.c
>>> index 2d691731c5..023716645f 100644
>>> --- a/libavcodec/h264dec.c
>>> +++ b/libavcodec/h264dec.c
>>> @@ -96,41 +96,6 @@ static void h264_er_decode_mb(void *opaque, int ref,
>> int mv_dir, int mv_type,
>>>      ff_h264_hl_decode_mb(h, &h->slice_ctx[0]);
>>>  }
>>>
>>> -void ff_h264_draw_horiz_band(const H264Context *h, H264SliceContext *sl,
>>> -                             int y, int height)
>>> -{
>>> -    AVCodecContext *avctx = h->avctx;
>>> -    const AVFrame   *src  = h->cur_pic.f;
>>> -    const AVPixFmtDescriptor *desc =
>> av_pix_fmt_desc_get(avctx->pix_fmt);
>>> -    int vshift = desc->log2_chroma_h;
>>> -    const int field_pic = h->picture_structure != PICT_FRAME;
>>> -    if (field_pic) {
>>> -        height <<= 1;
>>> -        y      <<= 1;
>>> -    }
>>> -
>>> -    height = FFMIN(height, avctx->height - y);
>>> -
>>> -    if (field_pic && h->first_field && !(avctx->slice_flags &
>> SLICE_FLAG_ALLOW_FIELD))
>>> -        return;
>>> -
>>> -    if (avctx->draw_horiz_band) {
>>> -        int offset[AV_NUM_DATA_POINTERS];
>>> -        int i;
>>> -
>>> -        offset[0] = y * src->linesize[0];
>>> -        offset[1] =
>>> -        offset[2] = (y >> vshift) * src->linesize[1];
>>> -        for (i = 3; i < AV_NUM_DATA_POINTERS; i++)
>>> -            offset[i] = 0;
>>> -
>>> -        emms_c();
>>> -
>>> -        avctx->draw_horiz_band(avctx, src, offset,
>>> -                               y, h->picture_structure, height);
>>> -    }
>>> -}
>>> -
>>>  void ff_h264_free_tables(H264Context *h)
>>>  {
>>>      int i;
>>> diff --git a/libavcodec/h264dec.h b/libavcodec/h264dec.h
>>> index 9a1ec1bace..28f62dbbba 100644
>>> --- a/libavcodec/h264dec.h
>>> +++ b/libavcodec/h264dec.h
>>> @@ -787,8 +787,6 @@ void ff_h264_unref_picture(H264Context *h,
>> H264Picture *pic);
>>>
>>>  void ff_h264_slice_context_init(H264Context *h, H264SliceContext *sl);
>>>
>>> -void ff_h264_draw_horiz_band(const H264Context *h, H264SliceContext
>> *sl, int y, int height);
>>> -
>>>  /**
>>>   * Submit a slice for decoding.
>>>   *
>>> diff --git a/libavcodec/vaapi_h264.c b/libavcodec/vaapi_h264.c
>>> index 9332aa6f31..386adae346 100644
>>> --- a/libavcodec/vaapi_h264.c
>>> +++ b/libavcodec/vaapi_h264.c
>>> @@ -311,17 +311,8 @@ static int vaapi_h264_end_frame(AVCodecContext
>> *avctx)
>>>  {
>>>      const H264Context *h = avctx->priv_data;
>>>      VAAPIDecodePicture *pic = h->cur_pic_ptr->hwaccel_picture_private;
>>> -    H264SliceContext *sl = &h->slice_ctx[0];
>>> -    int ret;
>>>
>>> -    ret = ff_vaapi_decode_issue(avctx, pic);
>>> -    if (ret < 0)
>>> -        goto finish;
>>> -
>>> -    ff_h264_draw_horiz_band(h, sl, 0, h->avctx->height);
>>> -
>>> -finish:
>>> -    return ret;
>>> +    return ff_vaapi_decode_issue(avctx, pic);
>>>  }
>>>
>>>  /** Decode the given H.264 slice with VA API. */
>>> diff --git a/libavcodec/vdpau_h264.c b/libavcodec/vdpau_h264.c
>>> index 525e208495..d39dbdd042 100644
>>> --- a/libavcodec/vdpau_h264.c
>>> +++ b/libavcodec/vdpau_h264.c
>>> @@ -201,7 +201,6 @@ static int vdpau_h264_decode_slice(AVCodecContext
>> *avctx,
>>>  static int vdpau_h264_end_frame(AVCodecContext *avctx)
>>>  {
>>>      H264Context *h = avctx->priv_data;
>>> -    H264SliceContext *sl = &h->slice_ctx[0];
>>>      H264Picture *pic = h->cur_pic_ptr;
>>>      struct vdpau_picture_context *pic_ctx =
>> pic->hwaccel_picture_private;
>>>      int val;
>>> @@ -210,7 +209,6 @@ static int vdpau_h264_end_frame(AVCodecContext
>> *avctx)
>>>      if (val < 0)
>>>          return val;
>>>
>>> -    ff_h264_draw_horiz_band(h, sl, 0, h->avctx->height);
>>>      return 0;
>>>  }
>>>
>>
>> Will apply this patch tomorrow unless there are objections.
>>
>> - Andreas
>>
> 
> Err...this used to work, what changed?
> 

As far as I know, this codec never had the AV_CODEC_CAP_DRAW_HORIZ_BAND
flag set (the commented out flag was removed in
e0c01a62adf59d1866ec53dcd76e4d4c815c5d58). Are you sure it ever worked?
Do you know someone who uses draw_horiz_band?
(Given the lack of the flag, ut would have been either illegal for the
caller to set draw_horiz_band or for the decoder to call it.)

- Andreas

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