On 06/03/14 12:09, Paulo Assis wrote: > Hi, > > 2014-03-05 23:01 GMT+00:00 William Manley <will@xxxxxxxxxxxxxxxxx>: >> Hi All >> >> I've been attempting to use the Logitech C920 with the uvcvideo driver. >> I set the controls with v4l2-ctl but some of them change during >> VIDIOC_STREAMON. My understanding is that the values of controls should >> be preserved. >> [snip] >> The camera does >> have a mode where it would change by itself but that is disabled >> (exposure_auto=1). > > This alone doesn't guarantee that exposure absolute is untouched. > To do so you need to set V4L2_CID_EXPOSURE_AUTO_PRIORITY to 0 and > V4L2_CID_EXPOSURE_AUTO to V4L2_EXPOSURE_MANUAL The behaviour is the same whether exposure_auto_priority is set to 1 or 0. I don't think I've explained myself clearly - the exposure time does not change by itself, apart from during VIDIOC_STREAMON: * When I'm streaming video from the camera it's constant. * When no data is coming from the camera it's constant It's only modified during STREAMON and when I explicitly set it with v4l2-ctl. This doesn't seem like correct behaviour as it breaks the use-case of setting the controls as you want before starting streaming. My workaround is to reset all the controls after calling VIDIOC_STREAMON but this is ugly and you get a few frames at the beginning of the video stream where the settings are set correctly. Thanks Will -- To unsubscribe from this list: send the line "unsubscribe linux-media" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
