[FFmpeg-devel] [PATCH 1/3] avcodec/dxva2_hevc: add support for parsing HEVC Range Extension data

[Steve Lhomme]

> On March 13, 2020 3:46 PM Hendrik Leppkes <h.leppkes at gmail.com> wrote:
> 
>  
> On Fri, Mar 13, 2020 at 11:25 AM Steve Lhomme <robux4 at ycbcr.xyz> wrote:
> >
> > Mimick the existing structure and add the extra fields from the Range Extension
> > in a wrapping structure.
> >
> > The FF_DXVA2_WORKAROUND_HEVC_REXT is set by the decoder user to signal the
> > selected decoder is expecting this extended structure rather than the default
> > one.
> > ---
> >  libavcodec/d3d11va.h    |  1 +
> >  libavcodec/dxva2.h      |  1 +
> >  libavcodec/dxva2_hevc.c | 79 ++++++++++++++++++++++++++++++++++++++---
> >  3 files changed, 76 insertions(+), 5 deletions(-)
> >
> > diff --git a/libavcodec/d3d11va.h b/libavcodec/d3d11va.h
> > index 6816b6c1e6..68a69c372d 100644
> > --- a/libavcodec/d3d11va.h
> > +++ b/libavcodec/d3d11va.h
> > @@ -47,6 +47,7 @@
> >
> >  #define FF_DXVA2_WORKAROUND_SCALING_LIST_ZIGZAG 1 ///< Work around for Direct3D11 and old UVD/UVD+ ATI video cards
> >  #define FF_DXVA2_WORKAROUND_INTEL_CLEARVIDEO    2 ///< Work around for Direct3D11 and old Intel GPUs with ClearVideo interface
> > +#define FF_DXVA2_WORKAROUND_HEVC_REXT           4 ///< Signal the D3D11VA decoder is using the HEVC Rext picture structure
> >
> >  /**
> >   * This structure is used to provides the necessary configurations and data
> > diff --git a/libavcodec/dxva2.h b/libavcodec/dxva2.h
> > index 22c93992f2..024999239d 100644
> > --- a/libavcodec/dxva2.h
> > +++ b/libavcodec/dxva2.h
> > @@ -47,6 +47,7 @@
> >
> >  #define FF_DXVA2_WORKAROUND_SCALING_LIST_ZIGZAG 1 ///< Work around for DXVA2 and old UVD/UVD+ ATI video cards
> >  #define FF_DXVA2_WORKAROUND_INTEL_CLEARVIDEO    2 ///< Work around for DXVA2 and old Intel GPUs with ClearVideo interface
> > +#define FF_DXVA2_WORKAROUND_HEVC_REXT           4 ///< Signal the DXVA2 decoder is using the HEVC Rext picture structure
> >
> >  /**
> >   * This structure is used to provides the necessary configurations and data
> > diff --git a/libavcodec/dxva2_hevc.c b/libavcodec/dxva2_hevc.c
> > index dbb701fb1c..98b3e74bd7 100644
> > --- a/libavcodec/dxva2_hevc.c
> > +++ b/libavcodec/dxva2_hevc.c
> > @@ -26,10 +26,47 @@
> >  #include "hevc_data.h"
> >  #include "hevcdec.h"
> >
> > +#pragma pack(push, 1)
> > +typedef struct
> > +{
> > +    DXVA_PicParams_HEVC main;
> > +
> > +    // HEVC Range Extension
> > +    __C89_NAMELESS union {
> > +        __C89_NAMELESS struct {
> > +            UINT32 transform_skip_rotation_enabled_flag : 1;
> > +            UINT32 transform_skip_context_enabled_flag : 1;
> > +            UINT32 implicit_rdpcm_enabled_flag : 1;
> > +            UINT32 explicit_rdpcm_enabled_flag : 1;
> > +            UINT32 extended_precision_processing_flag : 1;
> > +            UINT32 intra_smoothing_disabled_flag : 1;
> > +            UINT32 high_precision_offsets_enabled_flag : 1;
> > +            UINT32 persistent_rice_adaptation_enabled_flag : 1;
> > +            UINT32 cabac_bypass_alignment_enabled_flag : 1;
> > +            UINT32 cross_component_prediction_enabled_flag : 1;
> > +            UINT32 chroma_qp_offset_list_enabled_flag : 1;
> > +            UINT32 BitDepthLuma16 : 1; // TODO merge in ReservedBits5 if not needed
> > +            UINT32 BitDepthChroma16 : 1; // TODO merge in ReservedBits5 if not needed
> > +            UINT32 ReservedBits8 : 19;
> > +        };
> > +        UINT32 dwRangeExtensionFlags;
> > +    };
> > +
> > +    UCHAR diff_cu_chroma_qp_offset_depth;
> > +    UCHAR chroma_qp_offset_list_len_minus1;
> > +    UCHAR log2_sao_offset_scale_luma;
> > +    UCHAR log2_sao_offset_scale_chroma;
> > +    UCHAR log2_max_transform_skip_block_size_minus2;
> > +    CHAR cb_qp_offset_list[6];
> > +    CHAR cr_qp_offset_list[6];
> > +
> > +} DXVA_PicParams_HEVC_Rext;
> > +#pragma pack(pop)
> > +
> 
> Where is this struct specified? I don't see it in the latest released
> Windows SDK.

It is not. It is reversed engineered from the existing structure and wild guessing based on the HEVC Range Extension specs. The bits/fields are in the same order as the specs. Then I tested some GUIDs that output non 4:2:0 pixel formats on an Intel GPU that is known to decoder HEVC Range Extension.

Apparently NVIDIA doesn't provide DXVA GUIDs that output non 4:2:0 pixel formats on GPUs that supposedly decode HEVC 444 (likley nvdec only). AMD doesn't have such GPUs AFAIK.

So for now it's Intel only.