v4l2videoenc: forward caps query downstream before filtering

Closed Michael Grzeschik requested to merge mgrzeschik/gstreamer:v4l2videoenc-caps-reconf into main

The v4l2videoenc reported limited the caps in the sink query only by the formats supported on the V4L2 device. This is wrong if a downstream element has additional limits to the supported formats.

Pass the caps query to the videoencoder base class, which passes the query to downstream, and use the result as a basis for filtering and reporting the caps to upstream.

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