b3e089d415
In this commit, we enabled skip_try_fmt_probes quirk in order to speed up the start which is known to be disastrously slow with certain USB cameras. This has the side effect that we needed to rewrite the entire negotiation process in a way that we iterate over the possible caps until we find one that works. The new negotiation method consist of extracting a preferred structure from the peer caps and using this to fixate and sort the caps. To reflect the old behaviour, we sort all resolution strictly bigger to the preferred one with the closes one first. The rest is appended, keeping the same order. We then normalize the caps in case there was some list of interlace-mode or colorimetry left. We finally iterate over all fixed caps and try it. 99% of the time, the first or the second one should work, whit the result of a single S_FMT being issues. From there, it will be relatively easy to introduce new negotiation algorithm. The current algorithm is made for optimal image quality with a scaling sink that sets it's window resolution as preference. This the case if for: v4l2src ! videoconvert ! videoscale ! ximagesink Other strategy would be needed to optimize for non-scaling sink like ximagesink or kmssink when the driver does not scale. https://bugzilla.gnome.org/show_bug.cgi?id=785156
v4l2 plugins
============
The idea is a bit the same as the idea for the v4l1 plugins. We want
one generic v4l2element, and a few child objects (probably only two:
v4l2src and v4l2sink):
/-------- v4l2src
v4l2element ---=
\-------- v4l2sink
Both v4l2src and v4l2sink have a uncompressed and a compressed
recording-/playback-mode. Since this is all part of v4l2, the 'client'
of these elements, i.e. an application using v4l2src/v4l2sink, will
hardly notice this. All capsnego stuff is done inside, and the plugin
knows which formats are compressed and which are not.
Please note that the v4l1 and the v4l2 plugins are *not* compatible
concerning properties. Naming has been kept the same where possible,
but in some cases, properties had to be removed or added to make
full use of v4l2.
V4L2 API: http://linux.bytesex.org/v4l2/.
http://v4l2spec.bytesex.org/
/usr/include/linux/videodev2.h or
Kernel patches available from
http://dl.bytesex.org/patches/.
Articles:
http://lwn.net/Articles/203924/