Andreas Naumann b18031cf4b v4l2sink: Use V4L2_BUF_TYPE_VIDEO_OUTPUT_OVERLAY if driver advertises it.
On modern kernels, the G/S_FMT ioctls will always fail using
V4L2_BUF_TYPE_VIDEO_OVERLAY with VFL_DIR_TX (e.g. real overlay out drivers)
since this is not the intented use (rather rx, according to v4l2 API doc).
Probably this is why the Video Output Overlay interface was created, so if
the driver advertises it we might as well use.
For old kernels (pre 2012) the old way might still work so keeping this for
compatibility.

https://bugzilla.gnome.org/show_bug.cgi?id=761165
2016-06-06 17:26:13 -04:00
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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/