Re: [PATCHv2 08/12] pixfmt-compressed.rst: improve H264/HEVC/MPEG1+2/VP8+9 documentation

[Paul Kocialkowski <paul.kocialkowski@bootlin.com>]

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Hi,

On Mon 12 Aug 19, 13:05, Hans Verkuil wrote:
> The existing documentation was incorrect and did not correspond
> to how actual codec drivers implemented this.
> 
> Update the documentation to explicitly specify what is actually
> expected.
> 
> Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
> ---
>  .../media/uapi/v4l/pixfmt-compressed.rst      | 36 +++++++++++++++----
>  1 file changed, 30 insertions(+), 6 deletions(-)
> 
> diff --git a/Documentation/media/uapi/v4l/pixfmt-compressed.rst b/Documentation/media/uapi/v4l/pixfmt-compressed.rst
> index f52a7b67023d..9bb4a172a660 100644
> --- a/Documentation/media/uapi/v4l/pixfmt-compressed.rst
> +++ b/Documentation/media/uapi/v4l/pixfmt-compressed.rst
> @@ -41,7 +41,12 @@ Compressed Formats
>  
>        - ``V4L2_PIX_FMT_H264``
>        - 'H264'
> -      - H264 video elementary stream with start codes.
> +      - H264 Access Unit.
> +	The decoder expects one Access Unit per buffer.
> +	The encoder generates one Access Unit per buffer.
> +	If :ref:`VIDIOC_ENUM_FMT` reports ``V4L2_FMT_FLAG_CONTINUOUS_BYTESTREAM``
> +	then the decoder has no requirements since it can parse all the
> +	information from the raw bytestream.

Maybe it would be clearer to mention that "no requirements" concerns the
lack of frame/field boundary requirement? Otherwise it feels a bit unclear
what userspace is expected to do or not do depending on the flag.

Cheers,

Paul

>      * .. _V4L2-PIX-FMT-H264-NO-SC:
>  
>        - ``V4L2_PIX_FMT_H264_NO_SC``
> @@ -86,12 +91,20 @@ Compressed Formats
>  
>        - ``V4L2_PIX_FMT_MPEG1``
>        - 'MPG1'
> -      - MPEG1 video elementary stream.
> +      - MPEG1 Picture. Each buffer starts with a Picture header, followed
> +	by other headers as needed and ending with the Picture data.
> +	If :ref:`VIDIOC_ENUM_FMT` reports ``V4L2_FMT_FLAG_CONTINUOUS_BYTESTREAM``
> +	then the decoder has no requirements since it can parse all the
> +	information from the raw bytestream.
>      * .. _V4L2-PIX-FMT-MPEG2:
>  
>        - ``V4L2_PIX_FMT_MPEG2``
>        - 'MPG2'
> -      - MPEG2 video elementary stream.
> +      - MPEG2 Picture. Each buffer starts with a Picture header, followed
> +	by other headers as needed and ending with the Picture data.
> +	If :ref:`VIDIOC_ENUM_FMT` reports ``V4L2_FMT_FLAG_CONTINUOUS_BYTESTREAM``
> +	then the decoder has no requirements since it can parse all the
> +	information from the raw bytestream.
>      * .. _V4L2-PIX-FMT-MPEG2-SLICE:
>  
>        - ``V4L2_PIX_FMT_MPEG2_SLICE``
> @@ -132,7 +145,9 @@ Compressed Formats
>  
>        - ``V4L2_PIX_FMT_VP8``
>        - 'VP80'
> -      - VP8 video elementary stream.
> +      - VP8 compressed video frame. The encoder generates one
> +	compressed frame per buffer, and the decoder requires one
> +	compressed frame per buffer.
>      * .. _V4L2-PIX-FMT-VP8-FRAME:
>  
>        - ``V4L2_PIX_FMT_VP8_FRAME``
> @@ -157,12 +172,19 @@ Compressed Formats
>  
>        - ``V4L2_PIX_FMT_VP9``
>        - 'VP90'
> -      - VP9 video elementary stream.
> +      - VP9 compressed video frame. The encoder generates one
> +	compressed frame per buffer, and the decoder requires one
> +	compressed frame per buffer.
>      * .. _V4L2-PIX-FMT-HEVC:
>  
>        - ``V4L2_PIX_FMT_HEVC``
>        - 'HEVC'
> -      - HEVC/H.265 video elementary stream.
> +      - HEVC/H.265 Access Unit.
> +	The decoder expects one Access Unit per buffer.
> +	The encoder generates one Access Unit per buffer.
> +	If :ref:`VIDIOC_ENUM_FMT` reports ``V4L2_FMT_FLAG_CONTINUOUS_BYTESTREAM``
> +	then the decoder has no	requirements since it can parse all the
> +	information from the raw bytestream.
>      * .. _V4L2-PIX-FMT-FWHT:
>  
>        - ``V4L2_PIX_FMT_FWHT``
> @@ -170,6 +192,8 @@ Compressed Formats
>        - Video elementary stream using a codec based on the Fast Walsh Hadamard
>          Transform. This codec is implemented by the vicodec ('Virtual Codec')
>  	driver. See the codec-fwht.h header for more details.
> +	:ref:`VIDIOC_ENUM_FMT` reports ``V4L2_FMT_FLAG_CONTINUOUS_BYTESTREAM``
> +	since the decoder can parse all the information from the raw bytestream.
>      * .. _V4L2-PIX-FMT-FWHT-STATELESS:
>  
>        - ``V4L2_PIX_FMT_FWHT_STATELESS``
> -- 
> 2.20.1
> 

-- 
Paul Kocialkowski, Bootlin
Embedded Linux and kernel engineering
https://bootlin.com

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