WIP: v4l2: Fix alternate interlacing caps and field values

Copied from https://gitlab.freedesktop.org//gstreamer/gst-plugins-good/-/merge_requests/665

Alternate interlacing was broken for v4l2sink element and had some issues in caps reporting. The caps negotiation was also broken in many ways.


  • Ensure the following fails v4l2src ! video/x-raw\(format:Interlaced\),interlaced-mode=progressive ! fakevideosink
  • Ensure the following fails v4l2src ! video/x-raw,interlaced-mode=alternate ! fakevideosink
  • Investigate why all second fields are dropped with vivid

cc @gdesmott

Merge request reports