On Friday 11 September 2009 23:37:58 Mauro Carvalho Chehab wrote: > Em Fri, 11 Sep 2009 22:15:15 +0200 > Hans Verkuil <hverkuil@xxxxxxxxx> escreveu: > > > On Friday 11 September 2009 21:59:37 Mauro Carvalho Chehab wrote: > > > Em Fri, 11 Sep 2009 21:23:44 +0200 > > > Hans Verkuil <hverkuil@xxxxxxxxx> escreveu: > > > > > > > > In the case of resizer, I don't see why this can't be implemented as an ioctl > > > > > over /dev/video device. > > > > > > > > Well, no. Not in general. There are two problems. The first problem occurs if > > > > you have multiple instances of a resizer (OK, not likely, but you *can* have > > > > multiple video encoders or decoders or sensors). If all you have is the > > > > streaming device node, then you cannot select to which resizer (or video > > > > encoder) the ioctl should go. The media controller allows you to select the > > > > recipient of the ioctl explicitly. Thus providing the control that these > > > > applications need. > > > > > > This case doesn't apply, since, if you have multiple encoders and/or decoders, > > > you'll also have multiple /dev/video instances. All you need is to call it at > > > the right device you need to control. Am I missing something here? > > > > Typical use-case: two video decoders feed video into a composer that combines > > the two (e.g. for PiP) and streams the result to one video node. > > > > Now you want to change e.g. the contrast on one of those video decoders. That's > > not going to be possible using /dev/video. > > On your above example, each video decoder will need a /dev/video, and also the > video composer. Why? The video decoders do not do any streaming. There may well be just one DMA engine that DMAs the output from the video composer. Regards, Hans -- Hans Verkuil - video4linux developer - sponsored by TANDBERG Telecom -- 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
