linux-kernel - Re: [PATCH 1/2] media: add RealMedia format

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Message-ID: <88e1772841b84a786f4864a6540e03c2e7cd744b.camel@ndufresne.ca>
Date:   Wed, 11 Jan 2023 09:28:24 -0500
From:   Nicolas Dufresne <nicolas@...fresne.ca>
To:     Ming Qian <ming.qian@....com>, mchehab@...nel.org,
        hverkuil-cisco@...all.nl
Cc:     shawnguo@...nel.org, robh+dt@...nel.org, s.hauer@...gutronix.de,
        kernel@...gutronix.de, festevam@...il.com, linux-imx@....com,
        xiahong.bao@....com, ming.zhou@....com,
        linux-media@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH 1/2] media: add RealMedia format

Hi Ming,

sorry for the late reply ...

Le mardi 20 décembre 2022 à 16:39 +0800, Ming Qian a écrit :
> RealMedia is a proprietary multimedia container format
> created by RealNetworks with the filename extension .rm.
> RealMedia is generally used in conjunction with RealVideo and RealAudio,
> while also being used for streaming content over the Internet.
> 
> Signed-off-by: Ming Qian <ming.qian@....com>
> ---
>  .../userspace-api/media/v4l/pixfmt-compressed.rst     | 11 +++++++++++
>  drivers/media/v4l2-core/v4l2-ioctl.c                  |  1 +
>  include/uapi/linux/videodev2.h                        |  1 +
>  3 files changed, 13 insertions(+)
> 
> diff --git a/Documentation/userspace-api/media/v4l/pixfmt-compressed.rst b/Documentation/userspace-api/media/v4l/pixfmt-compressed.rst
> index 8794b92fde36..31ba2c00091e 100644
> --- a/Documentation/userspace-api/media/v4l/pixfmt-compressed.rst
> +++ b/Documentation/userspace-api/media/v4l/pixfmt-compressed.rst
> @@ -237,6 +237,17 @@ Compressed Formats
>          Metadata associated with the frame to decode is required to be passed
>          through the ``V4L2_CID_STATELESS_FWHT_PARAMS`` control.
>  	See the :ref:`associated Codec Control ID <codec-stateless-fwht>`.
> +    * .. _V4L2-PIX-FMT-RV:
> +
> +      - ``V4L2_PIX_FMT_RV``
> +      - 'RealMedia'
> +      - RealMedia is a proprietary multimedia container format
> +        created by RealNetworks with the filename extension .rm.
> +        RealMedia is generally used in conjunction with RealVideo and RealAudio,
> +        while also being used for streaming content over the Internet.
> +        Typically these streams are in CBR (constant bitrate),
> +        but a container for VBR (variable bitrate) streams
> +        named RMVB (RealMedia variable bitrate) has been developed.

I'm a bit confused with the description here. It describes the RealMedia (RM)
container format, but what you wanted is a RealVideo encoding (RV).

A quick search into FFMpeg (the only Open Source software decoder I could find),
the RealVideo comes in 4 incompatible flavours, RV10/RV20/RV30/RV40 also known
as  RealVideo 1 / G2 / 8 / 9+10. I think the format here should be a RealVideo
format, and it should specify the flavours you want to support (probably only
RV40).

regards,
Nicolas

>  
>  .. raw:: latex
>  
> diff --git a/drivers/media/v4l2-core/v4l2-ioctl.c b/drivers/media/v4l2-core/v4l2-ioctl.c
> index 9b5b04b8aa69..a4d12eea7fc5 100644
> --- a/drivers/media/v4l2-core/v4l2-ioctl.c
> +++ b/drivers/media/v4l2-core/v4l2-ioctl.c
> @@ -1473,6 +1473,7 @@ static void v4l_fill_fmtdesc(struct v4l2_fmtdesc *fmt)
>  		case V4L2_PIX_FMT_FWHT:		descr = "FWHT"; break; /* used in vicodec */
>  		case V4L2_PIX_FMT_FWHT_STATELESS:	descr = "FWHT Stateless"; break; /* used in vicodec */
>  		case V4L2_PIX_FMT_SPK:		descr = "Sorenson Spark"; break;
> +		case V4L2_PIX_FMT_RV:		descr = "RealMedia"; break;
>  		case V4L2_PIX_FMT_CPIA1:	descr = "GSPCA CPiA YUV"; break;
>  		case V4L2_PIX_FMT_WNVA:		descr = "WNVA"; break;
>  		case V4L2_PIX_FMT_SN9C10X:	descr = "GSPCA SN9C10X"; break;
> diff --git a/include/uapi/linux/videodev2.h b/include/uapi/linux/videodev2.h
> index 262ef10cfa02..a7a7969ae4f8 100644
> --- a/include/uapi/linux/videodev2.h
> +++ b/include/uapi/linux/videodev2.h
> @@ -740,6 +740,7 @@ struct v4l2_pix_format {
>  #define V4L2_PIX_FMT_H264_SLICE v4l2_fourcc('S', '2', '6', '4') /* H264 parsed slices */
>  #define V4L2_PIX_FMT_HEVC_SLICE v4l2_fourcc('S', '2', '6', '5') /* HEVC parsed slices */
>  #define V4L2_PIX_FMT_SPK      v4l2_fourcc('S', 'P', 'K', '0') /* Sorenson Spark */
> +#define V4L2_PIX_FMT_RV       v4l2_fourcc('R', 'V', '0', '0') /* RealMedia */
>  
>  /*  Vendor-specific formats   */
>  #define V4L2_PIX_FMT_CPIA1    v4l2_fourcc('C', 'P', 'I', 'A') /* cpia1 YUV */