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 the R-Car VSP1 1-D histogram engine metadata node, where did you link it in the media controller topology? Could you provide a (snippet of a) graph? Thanks Guennadi -- 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
