Similar to qtmux, but for mkv and webm containers.
Tested against other Gst elements and MPV. Note that the later
apparently does not show correct results for flipped values.
In particular the Yaw value seems to get ignored by many clients.
Can be tested with:
```
gst-launch-1.0 \
videotestsrc num-buffers=90 ! \
taginject tags="image-orientation=rotate-270" ! \
capsfilter caps=video/x-raw,width=640,height=480,max-framerate=30/1 ! \
videoconvert ! \
queue ! \
vp8enc ! \
queue ! \
webmmux ! \
filesink location=./test.webm
```
Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/8319>
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