Hello, On Monday, 1 October 2018 15:42:56 EEST Nicolas Dufresne wrote: > 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/gstv4l > 2object.c#n956 Some old code to give a bit of context: https://github.com/TimSC/mjpeg/ It should be feasible to implement a decoder that inserts the right Huffman table when none exists, but it has to be explicitly handled. An out-of-band mechanism to convey the information seems potentially useful to me. > > 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-compres > > sed.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, Laurent Pinchart
