Re: [RFC] V4L2_PIX_FMT_MJPEG vs V4L2_PIX_FMT_JPEG

[Mauro Carvalho Chehab <mchehab+samsung@kernel.org>]

Em Mon, 01 Oct 2018 08:42:56 -0400
Nicolas Dufresne <nicolas@ndufresne.ca> escreveu:

> 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

The code at libv4l handles both MJPEG and JPEG the same way. PJPG is
handled somewhat differently (although it uses the same code). There is a
code there that cleanups some Pixart-specific headers.

Thanks,
Mauro