Re: [PATCH v9 2/9] media: v4l: Add definitions for MPEG-2 slice format and metadata

From: Hans Verkuil
Date: Mon Sep 10 2018 - 05:45:31 EST


On 09/07/2018 12:24 AM, Paul Kocialkowski wrote:
> From: Paul Kocialkowski <paul.kocialkowski@xxxxxxxxxxx>
>
> Stateless video decoding engines require both the MPEG-2 slices and
> associated metadata from the video stream in order to decode frames.
>
> This introduces definitions for a new pixel format, describing buffers
> with MPEG-2 slice data, as well as control structure sfor passing the
> frame metadata to drivers.
>
> This is based on work from both Florent Revest and Hugues Fruchet.
>
> Signed-off-by: Paul Kocialkowski <paul.kocialkowski@xxxxxxxxxxx>
> ---
> .../media/uapi/v4l/extended-controls.rst | 176 ++++++++++++++++++
> .../media/uapi/v4l/pixfmt-compressed.rst | 16 ++
> .../media/uapi/v4l/vidioc-queryctrl.rst | 14 +-
> .../media/videodev2.h.rst.exceptions | 2 +
> drivers/media/v4l2-core/v4l2-ctrls.c | 63 +++++++
> drivers/media/v4l2-core/v4l2-ioctl.c | 1 +
> include/media/v4l2-ctrls.h | 18 +-
> include/uapi/linux/v4l2-controls.h | 65 +++++++
> include/uapi/linux/videodev2.h | 5 +
> 9 files changed, 351 insertions(+), 9 deletions(-)
>
> diff --git a/Documentation/media/uapi/v4l/extended-controls.rst b/Documentation/media/uapi/v4l/extended-controls.rst
> index 9f7312bf3365..f1951236266a 100644
> --- a/Documentation/media/uapi/v4l/extended-controls.rst
> +++ b/Documentation/media/uapi/v4l/extended-controls.rst
> @@ -1497,6 +1497,182 @@ enum v4l2_mpeg_video_h264_hierarchical_coding_type -
>
>
>
> +.. _v4l2-mpeg-mpeg2:
> +
> +``V4L2_CID_MPEG_VIDEO_MPEG2_SLICE_PARAMS (struct)``
> + Specifies the slice parameters (as extracted from the bitstream) for the
> + associated MPEG-2 slice data. This includes the necessary parameters for
> + configuring a stateless hardware decoding pipeline for MPEG-2.
> + The bitstream parameters are defined according to :ref:`mpeg2part2`.
> +
> +.. c:type:: v4l2_ctrl_mpeg2_slice_params
> +
> +.. cssclass:: longtable
> +
> +.. flat-table:: struct v4l2_ctrl_mpeg2_slice_params
> + :header-rows: 0
> + :stub-columns: 0
> + :widths: 1 1 2
> +
> + * - __u32
> + - ``bit_size``
> + - Size (in bits) of the current slice data.
> + * - __u32
> + - ``data_bit_offset``
> + - Offset (in bits) to the video data in the current slice data.
> + * - struct :c:type:`v4l2_mpeg2_sequence`
> + - ``sequence``
> + - Structure with MPEG-2 sequence metadata, merging relevant fields from
> + the sequence header and sequence extension parts of the bitstream.
> + * - struct :c:type:`v4l2_mpeg2_picture`
> + - ``picture``
> + - Structure with MPEG-2 picture metadata, merging relevant fields from
> + the picture header and picture coding extension parts of the bitstream.
> + * - __u8
> + - ``quantiser_scale_code``
> + - Code used to determine the quantization scale to use for the IDCT.
> + * - __u8
> + - ``backward_ref_index``
> + - Index for the V4L2 buffer to use as backward reference, used with
> + B-coded and P-coded frames.
> + * - __u8
> + - ``forward_ref_index``
> + - Index for the V4L2 buffer to use as forward reference, used with
> + P-coded frames.

Do these indices refer to the output or capture buffers? I think these should
refer to the output buffers, since this control is used in a request for the
output side.

Regards,

Hans