Hi Guennadi, On 01/11/2017 11:42 AM, Guennadi Liakhovetski wrote: > Hi Laurent, > > As you know, I'm working on a project, that involves streaming metadata, > obtained from UVC payload headers to the userspace. Luckily, you have > created "metadata node" patces a while ago. The core patch has also been > acked by Hans, so, I decided it would be a safe enough bet to base my work > on top of that. > > Your patch makes creating /dev/video* metadata device nodes possible, but > it doesn't provide any means to associate metadata nodes to respective > video (image) nodes. Another important aspect of using per-frame metadata > is synchronisation between metadata and image buffers. The user is > supposed to use buffer sequence numbers for that. That should be possible, > but might be difficult if buffers lose synchronisation at some point. As a > solution to the latter problem the use of requests with buffers for both > nodes has been proposed, which should be possible once the request API is > available. > > An alternative approach to metadata support, e.g. heterogeneous > multi-plain buffers with one plain carrying image data and another plain > carrying metadata would be possible. It could also have other uses. E.g. > we have come across cameras, streaming buffers, containing multiple images > (e.g. A and B). Possibly both images have supported fourcc format, but > they cannot be re-used, because A+B now are transferred in a single > buffer. Instead a new fourcc code has to be invented for such cases to > describe A+B. > > As an important argument in favour of having a separate video node for > metadata you named cases, when metadata has to be obtained before a > complete image is available. Do you remember specifically what those cases > are? Or have you got a link to that discussion? > > In any case, _if_ we do keep the current approach of separate /dev/video* > nodes, we need a way to associate video and metadata nodes. Earlier I > proposed using media controller links for that. In your implementation of I don't think that media controller links is a good idea. This metadata api could be used by mem2mem drivers which don't have media controller links so we will need a generic v4l2 way to bound image buffer and its metadata buffer. -- regards, Stan -- 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
