[FFmpeg-devel] [PATCH 1/2] hevcdec: Miss the location of chroma samples when exporting stream parameters

[Xiang, Haihao]

On Thu, 2018-05-17 at 12:30 +0200, Hendrik Leppkes wrote:
> On Thu, May 17, 2018 at 8:08 AM, Xiang, Haihao <haihao.xiang at intel.com> wrote:
> > On Wed, 2018-05-16 at 11:27 +0200, Hendrik Leppkes wrote:
> > > On Wed, May 16, 2018 at 10:49 AM, Xiang, Haihao <haihao.xiang at intel.com>
> > > wrote:
> > > > On Wed, 2018-05-16 at 10:17 +0200, Hendrik Leppkes wrote:
> > > > > On Wed, May 16, 2018 at 9:19 AM, Haihao Xiang <haihao.xiang at intel.com>
> > > > > wrote:
> > > > > > Signed-off-by: Haihao Xiang <haihao.xiang at intel.com>
> > > > > > ---
> > > > > >  libavcodec/hevcdec.c | 5 +++++
> > > > > >  1 file changed, 5 insertions(+)
> > > > > > 
> > > > > > diff --git a/libavcodec/hevcdec.c b/libavcodec/hevcdec.c
> > > > > > index c8877626d2..13d868bb4f 100644
> > > > > > --- a/libavcodec/hevcdec.c
> > > > > > +++ b/libavcodec/hevcdec.c
> > > > > > @@ -344,6 +344,11 @@ static void export_stream_params(AVCodecContext
> > > > > > *avctx,
> > > > > > const HEVCParamSets *ps,
> > > > > >          avctx->colorspace      = AVCOL_SPC_UNSPECIFIED;
> > > > > >      }
> > > > > > 
> > > > > > +    if (sps->vui.chroma_loc_info_present_flag)
> > > > > > +        avctx->chroma_sample_location = sps-
> > > > > > > vui.chroma_sample_loc_type_top_field + 1;
> > > > > > 
> > > > > > +    else
> > > > > > +        avctx->chroma_sample_location = AVCHROMA_LOC_UNSPECIFIED;
> > > > > > 
> > > > > 
> > > > > This change is incomplete, refer to the patch I proposed earlier:
> > > > > http://ffmpeg.org/pipermail/ffmpeg-devel/2018-April/228100.html
> > > > > 
> > > > 
> > > > Sorry I didn't see your proposal before. Per spec, once
> > > > chroma_loc_info_present_flag is set, chroma_format_idc should be 1. I
> > > > think
> > > > it
> > > > would be better to add some checks when parsing the sequence parameters.
> > > > 
> > > 
> > > It makes no real difference because you still need the check to be
> > > able to set the LEFT default value for  4:2:0 only.
> > 
> > If chroma_sample_loc_type_top_field is set correctly when parsing SPS, we
> > may
> > set chroma_sample_loc_type_top_field + 1 for 4:2:0 below no matter the
> > present
> > flag
> > 
> > if (sps->chroma_format_idc == 1)
> >     avctx->chroma_sample_location = sps-
> > >vui.chroma_sample_loc_type_top_field +
> > 1;
> > else
> >     avctx->chroma_sample_location = AVCHROMA_LOC_UNSPECIFIED;
> > 
> 
> The fields in the sps struct should reflect the bitstream,
> interpretation should be left out of it.
> 

Actually the checks for some field are done in sps, e.g.
def_disp_win_left_offset/def_disp_win_right_offset/def_disp_win_top_offset/
def_disp_win_bottom_offset. User needn't worry about the values when using these
fields.


> Like mentioned above, you always need the same checks anyway, all you
> do is move it into another place. It is IMHO much cleaner to keep the
> interpretation of all those values in the export_stream_params
> function, its not like its complex or anything, but it cleanly
> seperates parsing and interpretation, and ensures the sps struct only
> contains values directly read from the bitstream.
> 




> - Hendrik
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