Re: [RFC v2 09/10] media: uapi: h264: Add DPB entry field reference flags

[Jonas Karlman]

On 2019-10-31 11:20, Boris Brezillon wrote:
> On Tue, 29 Oct 2019 01:26:01 +0000
> Jonas Karlman <jonas@xxxxxxxxx> 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@xxxxxxxxx>
>> ---
>>  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

Hopefully I will have some time to rework and respin this at the end of next week.

Regards,
Jonas

>
>>  
>>  struct v4l2_h264_dpb_entry {
>>  	__u64 reference_ts;