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SubjectRe: [RFC v2 09/10] media: uapi: h264: Add DPB entry field reference flags
On Fri, 15 Nov 2019 06:26:54 +0000
Jonas Karlman <jonas@kwiboo.se> wrote:

> On 2019-10-31 11:20, Boris Brezillon wrote:
> > On Tue, 29 Oct 2019 01:26:01 +0000
> > Jonas Karlman <jonas@kwiboo.se> wrote:
> >
> >> Add DPB entry flags to help indicate when a reference frame is a field picture
> >> and how the DPB entry is referenced, top or bottom field or full frame.
> >>
> >> Signed-off-by: Jonas Karlman <jonas@kwiboo.se>
> >> ---
> >> Documentation/media/uapi/v4l/ext-ctrls-codec.rst | 12 ++++++++++++
> >> include/media/h264-ctrls.h | 4 ++++
> >> 2 files changed, 16 insertions(+)
> >>
> >> diff --git a/Documentation/media/uapi/v4l/ext-ctrls-codec.rst b/Documentation/media/uapi/v4l/ext-ctrls-codec.rst
> >> index 28313c0f4e7c..d472a54d1c4d 100644
> >> --- a/Documentation/media/uapi/v4l/ext-ctrls-codec.rst
> >> +++ b/Documentation/media/uapi/v4l/ext-ctrls-codec.rst
> >> @@ -2028,6 +2028,18 @@ enum v4l2_mpeg_video_h264_hierarchical_coding_type -
> >> * - ``V4L2_H264_DPB_ENTRY_FLAG_LONG_TERM``
> >> - 0x00000004
> >> - The DPB entry is a long term reference frame
> >> + * - ``V4L2_H264_DPB_ENTRY_FLAG_FIELD_PICTURE``
> >> + - 0x00000008
> >> + - The DPB entry is a field picture
> >> + * - ``V4L2_H264_DPB_ENTRY_FLAG_REF_TOP``
> >> + - 0x00000010
> >> + - The DPB entry is a top field reference
> >> + * - ``V4L2_H264_DPB_ENTRY_FLAG_REF_BOTTOM``
> >> + - 0x00000020
> >> + - The DPB entry is a bottom field reference
> >> + * - ``V4L2_H264_DPB_ENTRY_FLAG_REF_FRAME``
> >> + - 0x00000030
> >> + - The DPB entry is a reference frame
> >>
> >> ``V4L2_CID_MPEG_VIDEO_H264_DECODE_MODE (enum)``
> >> Specifies the decoding mode to use. Currently exposes slice-based and
> >> diff --git a/include/media/h264-ctrls.h b/include/media/h264-ctrls.h
> >> index e877bf1d537c..76020ebd1e6c 100644
> >> --- a/include/media/h264-ctrls.h
> >> +++ b/include/media/h264-ctrls.h
> >> @@ -185,6 +185,10 @@ struct v4l2_ctrl_h264_slice_params {
> >> #define V4L2_H264_DPB_ENTRY_FLAG_VALID 0x01
> >> #define V4L2_H264_DPB_ENTRY_FLAG_ACTIVE 0x02
> >> #define V4L2_H264_DPB_ENTRY_FLAG_LONG_TERM 0x04
> >> +#define V4L2_H264_DPB_ENTRY_FLAG_FIELD_PICTURE 0x08
> >> +#define V4L2_H264_DPB_ENTRY_FLAG_REF_TOP 0x10
> >> +#define V4L2_H264_DPB_ENTRY_FLAG_REF_BOTTOM 0x20
> >> +#define V4L2_H264_DPB_ENTRY_FLAG_REF_FRAME 0x30
> > I don't remember all the details, but do we really need 3 flags?
> > Maybe I'm wrong, but it looks like the following combination doesn't
> > make sense:
> >
> > - FIELD_PICTURE + REF_FRAME: if it's a full frame ref it should
> > contain both top and bottom fields right, so it's no longer a
> > FIELD_PICTURE, is it?
> >
> > Can't we just have 2 flags?
> >
> > FIELD_PICTURE 0x08
> > FIELD_REF_TOP 0x10 (meaning that FIELD_REF_BOTTOM is
> > 0x00)
> >
> > and then have the following combinations:
> >
> > top field ref => FIELD_PICTURE | FIELD_REF_TOP
> > bottom field ref => FIELD_PICTURE
> > full frame ref => 0x0
>
> I am not sure and will need to look closer at spec and what ffmpeg is doing.
> These flags was mostly inspired by the information ffmpeg stores in
> H264Picture->reference and H264Picture->field_picture.
>
> I also believe that the new FLAG_REF_TOP/BOTTOM may make FLAG_ACTIVE obsolete.
>
> active => flags & FLAG_REF_FRAME

Can't we keep the ACTIVE flag and drop the REF_FRAME one then? AFAIU,
all we need to know in addition to what we already have is:

* is the reference a full-frame or a field?
* if it is a field, which one (top or bottom)?

Hence my suggestion to keep only 2 flags.

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