Currently, read() call from /dev/video entry of an USB camera is returning invalid argument error. This is quite common for userspace application to read compressed data such as JPEG from /dev/video then redirect those data to a multimedia player or any other compressed format consumer, see [1].
There was a tentative of implementation in the past [2] but it was prior to switch on vb2 helpers usage inside uvc. Now that vb2 is in place, we can implement read support using vb2_read() helper. Tested with Logitech HD Webcam C525 using v4l2-ctl to configure camera then GStreamer player to play stream: $> v4l2-ctl -d /dev/video0 --set-fmt-video=width=640,height=480,pixelformat=MJPG $> gst-play-1.0 /dev/video0 [1] http://credentiality2.blogspot.com/2010/04/v4l2-example.html?_sm_au_=ikcQHNZZFn2Rqft5 https://stackoverrun.com/fr/q/4215615 https://stackoverflow.com/questions/36297390/read-function-for-webcam-device-in-v4l2-fails-with-invalid-argument https://stackoverflow.com/questions/31058571/reading-camera-input-from-dev-video0-in-python-or-c [2] https://www.mail-archive.com/linux-uvc-devel@lists.berlios.de/msg01258.html Hugues Fruchet (1): media: uvcvideo: Read support drivers/media/usb/uvc/uvc_queue.c | 15 ++++++++++++++- drivers/media/usb/uvc/uvc_v4l2.c | 11 ++++++++--- drivers/media/usb/uvc/uvcvideo.h | 2 ++ 3 files changed, 24 insertions(+), 4 deletions(-) -- 2.7.4
