This add src format validation, this avoid registering element for
drivers we don't support any of their src formats. This also special
case the AlphaDecodeBin wrapper, as we know that alphacombine element
only support I420 and NV12 for now.
Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-bad/-/merge_requests/2272>
This introduces the skeleton of the H264 decoder. The plugin will list the
devices and register a subclass of the GstV4L2CodecH264Dec base class. The
subclass will pick the required specific information from the GstV4L2Device
stored in the subclass structure.
This introduces a GstV4L2CodecDevice structure and helper to retrieve a
list of CODEC device drivers. In order to find the device driver we
enumerate all media devices with UDEV. We then get the media controller
topology and locate a entity with function encoder or decoder and make
sure it is linked to two V4L2 IO entity pointing to the same device
node.
