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Message-ID: <29bc7b9ffd2ca761cc6df88ff113bb6bcc844e1d.camel@collabora.com>
Subject: Re: [RFC] V4L2_PIX_FMT_MJPEG vs V4L2_PIX_FMT_JPEG
From: Ezequiel Garcia <ezequiel@collabora.com>
To: Nicolas Dufresne <nicolas@ndufresne.ca>,
        Hans Verkuil <hverkuil@xs4all.nl>,
        Linux Media Mailing List <linux-media@vger.kernel.org>
Cc: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Date: Mon, 01 Oct 2018 13:12:01 -0300
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On Mon, 2018-10-01 at 08:42 -0400, Nicolas Dufresne wrote:
> Hello Hans,
> 
> Le lundi 01 octobre 2018 à 10:43 +0200, Hans Verkuil a écrit :
> > It turns out that we have both JPEG and Motion-JPEG pixel formats defined.
> > 
> > Furthermore, some drivers support one, some the other and some both.
> > 
> > These pixelformats both mean the same.
> > 
> > I propose that we settle on JPEG (since it seems to be used most often) and
> > add JPEG support to those drivers that currently only use MJPEG.
> 
> Thanks for looking into this. As per GStreamer code, I see 3 alias for
> JPEG. V4L2_PIX_FMT_MJPEG/JPEG/PJPG. I don't know the context, this code
> was written before I knew GStreamer existed. It's possible there is a
> subtle difference, I have never looked at it, but clearly all our JPEG
> decoder handle these as being the same.
> 
> https://cgit.freedesktop.org/gstreamer/gst-plugins-good/tree/sys/v4l2/gstv4l2object.c#n956
> 

To add more data points on the gstreamer side, there's really no difference
between gstreamer's types image/jpeg and video/x-jpeg.

Notably, jpegdec element just stuffs a huffman table if one is missing,
for any jpeg:

https://cgit.freedesktop.org/gstreamer/gst-plugins-good/tree/ext/jpeg/gstjpegdec.c#n584

> > 
> > We also need to update the V4L2_PIX_FMT_JPEG documentation since it just says
> > TBD:
> > 
> > https://www.linuxtv.org/downloads/v4l-dvb-apis-new/uapi/v4l/pixfmt-compressed.html
> > 
> > $ git grep -l V4L2_PIX_FMT_MJPEG
> > drivers/media/pci/meye/meye.c
> > drivers/media/pci/solo6x10/solo6x10-v4l2-enc.c
> > drivers/media/platform/sti/delta/delta-cfg.h
> > drivers/media/platform/sti/delta/delta-mjpeg-dec.c
> > drivers/media/usb/cpia2/cpia2_v4l.c
> > drivers/media/usb/go7007/go7007-driver.c
> > drivers/media/usb/go7007/go7007-fw.c
> > drivers/media/usb/go7007/go7007-v4l2.c
> > drivers/media/usb/s2255/s2255drv.c
> > drivers/media/usb/uvc/uvc_driver.c
> > drivers/staging/media/zoran/zoran_driver.c
> > drivers/staging/vc04_services/bcm2835-camera/bcm2835-camera.c
> > drivers/usb/gadget/function/uvc_v4l2.c
> > 
> > It looks like s2255 and cpia2 support both already, so that would leave
> > 8 drivers that need to be modified, uvc being the most important of the
> > lot.
> > 
> > Any comments?
> > 
> > Regards,
> > 
> > 	Hans
> 
>